diff --git a/DOCS.md b/DOCS.md
index 833f93e..ea2fd06 100644
--- a/DOCS.md
+++ b/DOCS.md
@@ -509,6 +509,34 @@ The symbol `|` can be used to denote that the following fraction symbols are 1 "
 
 A single "set" of fraction symbols can only represent up to 11/12, as 12/12 can be written as 1.
 
+### IASON
+
+> ⚠ **Warning.** The `IASON` module enables your program to read and write non-Roman numerals. Numbers handled by `IASON_LEGE` and `IASON_SCRIBE` use the decimal digits `0`–`9` (e.g. `42`, `1789`, `30`), not Roman numerals. This goes against the design philosophy of CENTVRION and should not be used unless absolutely necessary.
+
+![CVM IASON](snippets/iason.png)
+
+The `IASON` module adds two builtins for converting between `CENTVRION` values and JSON strings.
+
+`IASON_LEGE(string)` parses a JSON string and returns the corresponding `CENTVRION` value. Mappings: JSON `null` → `NVLLVS`, `true`/`false` → `VERITAS`/`FALSITAS`, integer → numeral, string → string, array → array, object → `TABVLA` (string keys).
+
+JSON floats with no fractional part (e.g. `3.0`) come back as integers. Other floats depend on whether the `FRACTIO` module is also loaded: with `FRACTIO`, `0.1` parses to the exact fraction `I:|::|::|S:.|S.|:` (1/10); without it, the value is floored to the nearest integer.
+
+![IASON_LEGE example](snippets/iason_lege.png)
+
+```
+> Marcus
+> XXX
+> [gladius scutum]
+```
+
+`IASON_SCRIBE(value)` serializes a `CENTVRION` value to a JSON string. Integers and fractions become JSON numbers (fractions via shortest-round-trip float), strings become JSON strings (with the standard escapes), arrays become arrays, dicts become objects (insertion order preserved). Functions and dicts with non-string keys raise an error.
+
+![IASON_SCRIBE example](snippets/iason_scribe.png)
+
+```
+> {"nomen": "Marcus", "anni": 30}
+```
+
 ### MAGNVM
 ![CVM MAGNVM](snippets/magnvm.png)
 
diff --git a/cent b/cent
index 8371069..1d0a886 100755
--- a/cent
+++ b/cent
@@ -53,17 +53,19 @@ def main():
         sys.exit(f"CENTVRION error: {e}")
     else:
       c_source = compile_program(program)
-      runtime_c = os.path.join(
+      runtime_dir = os.path.join(
         os.path.dirname(__file__),
-        "centvrion", "compiler", "runtime", "cent_runtime.c"
+        "centvrion", "compiler", "runtime"
       )
+      runtime_c = os.path.join(runtime_dir, "cent_runtime.c")
+      iason_c = os.path.join(runtime_dir, "cent_iason.c")
       out_path = os.path.splitext(file_path)[0]
       if args["--keep-c"]:
         tmp_path = out_path + ".c"
         with open(tmp_path, "w") as f:
           f.write(c_source)
         subprocess.run(
-          ["gcc", "-O2", tmp_path, runtime_c, "-o", out_path, "-lcurl", "-lmicrohttpd"],
+          ["gcc", "-O2", tmp_path, runtime_c, iason_c, "-o", out_path, "-lcurl", "-lmicrohttpd", "-lm"],
           check=True,
         )
       else:
@@ -72,7 +74,7 @@ def main():
           tmp_path = tmp.name
         try:
           subprocess.run(
-            ["gcc", "-O2", tmp_path, runtime_c, "-o", out_path, "-lcurl", "-lmicrohttpd"],
+            ["gcc", "-O2", tmp_path, runtime_c, iason_c, "-o", out_path, "-lcurl", "-lmicrohttpd", "-lm"],
             check=True,
           )
         finally:
diff --git a/centvrion/ast_nodes.py b/centvrion/ast_nodes.py
index c4f3917..6d90aaa 100644
--- a/centvrion/ast_nodes.py
+++ b/centvrion/ast_nodes.py
@@ -1,5 +1,7 @@
 import functools
 import http.server
+import json
+import math
 import re
 import time
 import urllib.parse
@@ -290,6 +292,51 @@ def frac_to_fraction(s, magnvm=False, svbnvlla=False):
 
   return total
 
+def _json_to_val(obj):
+  if obj is None:
+    return ValNul()
+  if isinstance(obj, bool):
+    return ValBool(obj)
+  if isinstance(obj, int):
+    return ValInt(obj)
+  if isinstance(obj, Fraction):
+    if obj.denominator == 1:
+      return ValInt(obj.numerator)
+    return ValFrac(obj)
+  if isinstance(obj, str):
+    return ValStr(obj)
+  if isinstance(obj, list):
+    return ValList([_json_to_val(x) for x in obj])
+  if isinstance(obj, dict):
+    return ValDict({k: _json_to_val(v) for k, v in obj.items()})
+  raise CentvrionError(f"IASON_LEGE: unsupported JSON value of type {type(obj).__name__}")
+
+
+def _val_to_json(val):
+  if isinstance(val, ValNul):
+    return None
+  if isinstance(val, ValBool):
+    return val.value()
+  if isinstance(val, ValInt):
+    return val.value()
+  if isinstance(val, ValFrac):
+    return float(val.value())
+  if isinstance(val, ValStr):
+    return val.value()
+  if isinstance(val, ValList):
+    return [_val_to_json(x) for x in val.value()]
+  if isinstance(val, ValDict):
+    out = {}
+    for k, v in val.value().items():
+      if not isinstance(k, str):
+        raise CentvrionError("IASON_SCRIBE: dict keys must be strings to serialize as JSON")
+      out[k] = _val_to_json(v)
+    return out
+  if isinstance(val, ValFunc):
+    raise CentvrionError("IASON_SCRIBE: cannot serialize a function")
+  raise CentvrionError(f"IASON_SCRIBE: cannot serialize value of type {type(val).__name__}")
+
+
 def fraction_to_frac(f, magnvm=False, svbnvlla=False) -> str:
   if f < 0:
     if not svbnvlla:
@@ -1782,6 +1829,30 @@ class BuiltIn(Node):
         server = http.server.HTTPServer(("0.0.0.0", port.value()), _CentHandler)
         server.serve_forever()
         return vtable, ValNul()
+      case "IASON_LEGE":
+        if "IASON" not in vtable["#modules"]:
+          raise CentvrionError("Cannot use 'IASON_LEGE' without module 'IASON'")
+        if len(params) != 1:
+          raise CentvrionError("IASON_LEGE takes exactly I argument")
+        s = params[0]
+        if not isinstance(s, ValStr):
+          raise CentvrionError("IASON_LEGE requires a string")
+        fractio = "FRACTIO" in vtable["#modules"]
+        try:
+          if fractio:
+            parsed = json.loads(s.value(), parse_float=Fraction)
+          else:
+            parsed = json.loads(s.value(), parse_float=lambda x: math.floor(float(x)))
+        except json.JSONDecodeError as e:
+          raise CentvrionError(f"IASON_LEGE: invalid JSON: {e.msg}")
+        return vtable, _json_to_val(parsed)
+      case "IASON_SCRIBE":
+        if "IASON" not in vtable["#modules"]:
+          raise CentvrionError("Cannot use 'IASON_SCRIBE' without module 'IASON'")
+        if len(params) != 1:
+          raise CentvrionError("IASON_SCRIBE takes exactly I argument")
+        obj = _val_to_json(params[0])
+        return vtable, ValStr(json.dumps(obj, ensure_ascii=False))
       case _:
         raise NotImplementedError(self.builtin)
 
diff --git a/centvrion/compiler/emit_expr.py b/centvrion/compiler/emit_expr.py
index c95a185..328d978 100644
--- a/centvrion/compiler/emit_expr.py
+++ b/centvrion/compiler/emit_expr.py
@@ -437,6 +437,25 @@ def _emit_builtin(node, ctx):
         lines.append(f"cent_avscvlta({param_vars[0]});")
         lines.append(f"CentValue {tmp} = cent_null();")
 
+    case "IASON_LEGE":
+      if not ctx.has_module("IASON"):
+        lines.append('cent_runtime_error("IASON module required for IASON_LEGE");')
+        lines.append(f"CentValue {tmp} = cent_null();")
+      elif len(param_vars) != 1:
+        raise _err(node, "IASON_LEGE takes exactly I argument")
+      else:
+        fractio_flag = "1" if ctx.has_module("FRACTIO") else "0"
+        lines.append(f"CentValue {tmp} = cent_iason_lege({param_vars[0]}, {fractio_flag});")
+
+    case "IASON_SCRIBE":
+      if not ctx.has_module("IASON"):
+        lines.append('cent_runtime_error("IASON module required for IASON_SCRIBE");')
+        lines.append(f"CentValue {tmp} = cent_null();")
+      elif len(param_vars) != 1:
+        raise _err(node, "IASON_SCRIBE takes exactly I argument")
+      else:
+        lines.append(f"CentValue {tmp} = cent_iason_scribe({param_vars[0]});")
+
     case _:
       raise NotImplementedError(node.builtin)
 
diff --git a/centvrion/compiler/emitter.py b/centvrion/compiler/emitter.py
index 4ca6768..0bb4992 100644
--- a/centvrion/compiler/emitter.py
+++ b/centvrion/compiler/emitter.py
@@ -58,6 +58,7 @@ def compile_program(program):
   # Includes
   lines += [
     f'#include "{_RUNTIME_DIR}/cent_runtime.h"',
+    f'#include "{_RUNTIME_DIR}/cent_iason.h"',
     "",
   ]
 
diff --git a/centvrion/compiler/runtime/cent_iason.c b/centvrion/compiler/runtime/cent_iason.c
new file mode 100644
index 0000000..54c16cf
--- /dev/null
+++ b/centvrion/compiler/runtime/cent_iason.c
@@ -0,0 +1,426 @@
+#include "cent_iason.h"
+
+#include <ctype.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* ---------- shared helpers ----------------------------------------- */
+
+static long iason_gcd(long a, long b) {
+  if (a < 0) a = -a;
+  if (b < 0) b = -b;
+  while (b) { long t = b; b = a % b; a = t; }
+  return a ? a : 1;
+}
+
+static CentValue iason_frac_reduce(long num, long den) {
+  if (den < 0) { num = -num; den = -den; }
+  long g = iason_gcd(num, den);
+  num /= g; den /= g;
+  if (den == 1) return cent_int(num);
+  return cent_frac(num, den);
+}
+
+/* ---------- parser ------------------------------------------------- */
+
+typedef struct {
+  const char *src;
+  size_t      pos;
+  size_t      len;
+  int         fractio;
+} IasonParser;
+
+static void iason_die(const char *msg) {
+  cent_runtime_error(msg);
+}
+
+static void iason_skip_ws(IasonParser *p) {
+  while (p->pos < p->len) {
+    char c = p->src[p->pos];
+    if (c == ' ' || c == '\t' || c == '\n' || c == '\r') p->pos++;
+    else break;
+  }
+}
+
+static int iason_peek(IasonParser *p) {
+  return (p->pos < p->len) ? (unsigned char)p->src[p->pos] : -1;
+}
+
+static void iason_expect(IasonParser *p, char c, const char *msg) {
+  if (p->pos >= p->len || p->src[p->pos] != c)
+    iason_die(msg);
+  p->pos++;
+}
+
+static void iason_expect_word(IasonParser *p, const char *word) {
+  size_t n = strlen(word);
+  if (p->len - p->pos < n || memcmp(p->src + p->pos, word, n) != 0)
+    iason_die("IASON_LEGE: invalid JSON literal");
+  p->pos += n;
+}
+
+/* Encode a Unicode codepoint as UTF-8 into buf; returns bytes written. */
+static int iason_utf8_encode(unsigned cp, char *buf) {
+  if (cp <= 0x7F)        { buf[0] = (char)cp; return 1; }
+  if (cp <= 0x7FF)       { buf[0] = (char)(0xC0 | (cp >> 6));
+                           buf[1] = (char)(0x80 | (cp & 0x3F)); return 2; }
+  if (cp <= 0xFFFF)      { buf[0] = (char)(0xE0 | (cp >> 12));
+                           buf[1] = (char)(0x80 | ((cp >> 6) & 0x3F));
+                           buf[2] = (char)(0x80 | (cp & 0x3F)); return 3; }
+  if (cp <= 0x10FFFF)    { buf[0] = (char)(0xF0 | (cp >> 18));
+                           buf[1] = (char)(0x80 | ((cp >> 12) & 0x3F));
+                           buf[2] = (char)(0x80 | ((cp >> 6) & 0x3F));
+                           buf[3] = (char)(0x80 | (cp & 0x3F)); return 4; }
+  iason_die("IASON_LEGE: codepoint out of range");
+  return 0;
+}
+
+static unsigned iason_read_hex4(IasonParser *p) {
+  if (p->len - p->pos < 4) iason_die("IASON_LEGE: truncated \\u escape");
+  unsigned v = 0;
+  for (int i = 0; i < 4; i++) {
+    char c = p->src[p->pos++];
+    v <<= 4;
+    if      (c >= '0' && c <= '9') v |= c - '0';
+    else if (c >= 'a' && c <= 'f') v |= c - 'a' + 10;
+    else if (c >= 'A' && c <= 'F') v |= c - 'A' + 10;
+    else iason_die("IASON_LEGE: invalid hex in \\u escape");
+  }
+  return v;
+}
+
+/* Parses a JSON string literal at p->pos (positioned at the opening "),
+   returns an arena-allocated NUL-terminated UTF-8 string. */
+static char *iason_parse_string(IasonParser *p) {
+  iason_expect(p, '"', "IASON_LEGE: expected string");
+  /* upper bound on output: same as remaining input (escapes shrink). */
+  size_t cap = (p->len - p->pos) + 1;
+  char *buf = cent_arena_alloc(cent_arena, cap);
+  size_t out = 0;
+  while (p->pos < p->len) {
+    unsigned char c = (unsigned char)p->src[p->pos++];
+    if (c == '"') { buf[out] = '\0'; return buf; }
+    if (c == '\\') {
+      if (p->pos >= p->len) iason_die("IASON_LEGE: trailing \\ in string");
+      char esc = p->src[p->pos++];
+      switch (esc) {
+        case '"':  buf[out++] = '"';  break;
+        case '\\': buf[out++] = '\\'; break;
+        case '/':  buf[out++] = '/';  break;
+        case 'b':  buf[out++] = '\b'; break;
+        case 'f':  buf[out++] = '\f'; break;
+        case 'n':  buf[out++] = '\n'; break;
+        case 'r':  buf[out++] = '\r'; break;
+        case 't':  buf[out++] = '\t'; break;
+        case 'u': {
+          unsigned cp = iason_read_hex4(p);
+          if (cp >= 0xD800 && cp <= 0xDBFF) {
+            /* high surrogate; expect \uXXXX low surrogate */
+            if (p->len - p->pos < 6 || p->src[p->pos] != '\\' || p->src[p->pos + 1] != 'u')
+              iason_die("IASON_LEGE: missing low surrogate after high surrogate");
+            p->pos += 2;
+            unsigned lo = iason_read_hex4(p);
+            if (lo < 0xDC00 || lo > 0xDFFF)
+              iason_die("IASON_LEGE: invalid low surrogate");
+            cp = 0x10000 + (((cp - 0xD800) << 10) | (lo - 0xDC00));
+          } else if (cp >= 0xDC00 && cp <= 0xDFFF) {
+            iason_die("IASON_LEGE: stray low surrogate");
+          }
+          out += iason_utf8_encode(cp, buf + out);
+          break;
+        }
+        default: iason_die("IASON_LEGE: invalid escape sequence");
+      }
+    } else if (c < 0x20) {
+      iason_die("IASON_LEGE: unescaped control character in string");
+    } else {
+      buf[out++] = (char)c;
+    }
+  }
+  iason_die("IASON_LEGE: unterminated string");
+  return NULL;
+}
+
+/* Cap on fractional digits parsed exactly; beyond this we truncate to
+   keep `long` arithmetic safe (10^18 fits in int64). */
+#define IASON_MAX_FRAC_DIGITS 18
+
+static CentValue iason_parse_number(IasonParser *p) {
+  size_t start = p->pos;
+  int negative = 0;
+  if (p->src[p->pos] == '-') { negative = 1; p->pos++; }
+
+  /* Integer part. */
+  if (p->pos >= p->len || !isdigit((unsigned char)p->src[p->pos]))
+    iason_die("IASON_LEGE: invalid number");
+  if (p->src[p->pos] == '0') {
+    p->pos++;
+  } else {
+    while (p->pos < p->len && isdigit((unsigned char)p->src[p->pos])) p->pos++;
+  }
+
+  int has_frac = 0, has_exp = 0;
+  size_t frac_start = 0, frac_end = 0;
+  if (p->pos < p->len && p->src[p->pos] == '.') {
+    has_frac = 1;
+    p->pos++;
+    frac_start = p->pos;
+    if (p->pos >= p->len || !isdigit((unsigned char)p->src[p->pos]))
+      iason_die("IASON_LEGE: invalid number");
+    while (p->pos < p->len && isdigit((unsigned char)p->src[p->pos])) p->pos++;
+    frac_end = p->pos;
+  }
+  long exp = 0;
+  if (p->pos < p->len && (p->src[p->pos] == 'e' || p->src[p->pos] == 'E')) {
+    has_exp = 1;
+    p->pos++;
+    int esign = 1;
+    if (p->pos < p->len && (p->src[p->pos] == '+' || p->src[p->pos] == '-')) {
+      if (p->src[p->pos] == '-') esign = -1;
+      p->pos++;
+    }
+    if (p->pos >= p->len || !isdigit((unsigned char)p->src[p->pos]))
+      iason_die("IASON_LEGE: invalid number");
+    while (p->pos < p->len && isdigit((unsigned char)p->src[p->pos])) {
+      exp = exp * 10 + (p->src[p->pos] - '0');
+      p->pos++;
+    }
+    exp *= esign;
+  }
+
+  size_t end = p->pos;
+
+  if (!has_frac && !has_exp) {
+    /* Pure integer. Use strtol-style parse (we already validated digits). */
+    long v = 0;
+    for (size_t i = (negative ? start + 1 : start); i < end; i++) {
+      v = v * 10 + (p->src[i] - '0');
+    }
+    return cent_int(negative ? -v : v);
+  }
+
+  if (!p->fractio) {
+    /* Floor to int. strtod handles the full grammar here. */
+    char *tmp = cent_arena_alloc(cent_arena, end - start + 1);
+    memcpy(tmp, p->src + start, end - start);
+    tmp[end - start] = '\0';
+    double d = strtod(tmp, NULL);
+    return cent_int((long)floor(d));
+  }
+
+  /* FRACTIO loaded: build an exact fraction from the decimal/exponent form. */
+  long num = 0;
+  /* Integer-part digits */
+  size_t int_start = negative ? start + 1 : start;
+  size_t int_end = has_frac ? (frac_start - 1) : (has_exp ? end - 0 : end);
+  /* If we have an exponent without a fraction part, find where digits end. */
+  if (has_exp && !has_frac) {
+    int_end = int_start;
+    while (int_end < p->len && isdigit((unsigned char)p->src[int_end])) int_end++;
+  }
+  for (size_t i = int_start; i < int_end; i++) {
+    num = num * 10 + (p->src[i] - '0');
+  }
+  /* Fractional digits, capped */
+  long den = 1;
+  if (has_frac) {
+    size_t take = frac_end - frac_start;
+    if (take > IASON_MAX_FRAC_DIGITS) take = IASON_MAX_FRAC_DIGITS;
+    for (size_t i = 0; i < take; i++) {
+      num = num * 10 + (p->src[frac_start + i] - '0');
+      den *= 10;
+    }
+  }
+  if (negative) num = -num;
+  /* Apply exponent: positive shifts num, negative shifts den. */
+  while (exp > 0) { num *= 10; exp--; }
+  while (exp < 0) { den *= 10; exp++; }
+  return iason_frac_reduce(num, den);
+}
+
+static CentValue iason_parse_value(IasonParser *p);
+
+static CentValue iason_parse_array(IasonParser *p) {
+  iason_expect(p, '[', "IASON_LEGE: expected [");
+  iason_skip_ws(p);
+  CentValue lst = cent_list_new(4);
+  if (iason_peek(p) == ']') { p->pos++; return lst; }
+  for (;;) {
+    iason_skip_ws(p);
+    CentValue elem = iason_parse_value(p);
+    cent_list_push(&lst, elem);
+    iason_skip_ws(p);
+    int c = iason_peek(p);
+    if (c == ',') { p->pos++; continue; }
+    if (c == ']') { p->pos++; return lst; }
+    iason_die("IASON_LEGE: expected , or ] in array");
+  }
+}
+
+static CentValue iason_parse_object(IasonParser *p) {
+  iason_expect(p, '{', "IASON_LEGE: expected {");
+  iason_skip_ws(p);
+  CentValue d = cent_dict_new(4);
+  if (iason_peek(p) == '}') { p->pos++; return d; }
+  for (;;) {
+    iason_skip_ws(p);
+    if (iason_peek(p) != '"') iason_die("IASON_LEGE: object key must be a string");
+    char *key = iason_parse_string(p);
+    iason_skip_ws(p);
+    iason_expect(p, ':', "IASON_LEGE: expected : after object key");
+    iason_skip_ws(p);
+    CentValue val = iason_parse_value(p);
+    cent_dict_set(&d, cent_str(key), val);
+    iason_skip_ws(p);
+    int c = iason_peek(p);
+    if (c == ',') { p->pos++; continue; }
+    if (c == '}') { p->pos++; return d; }
+    iason_die("IASON_LEGE: expected , or } in object");
+  }
+}
+
+static CentValue iason_parse_value(IasonParser *p) {
+  iason_skip_ws(p);
+  int c = iason_peek(p);
+  if (c < 0) iason_die("IASON_LEGE: unexpected end of input");
+  if (c == '{') return iason_parse_object(p);
+  if (c == '[') return iason_parse_array(p);
+  if (c == '"') return cent_str(iason_parse_string(p));
+  if (c == 't') { iason_expect_word(p, "true");  return cent_bool(1); }
+  if (c == 'f') { iason_expect_word(p, "false"); return cent_bool(0); }
+  if (c == 'n') { iason_expect_word(p, "null");  return cent_null(); }
+  if (c == '-' || (c >= '0' && c <= '9')) return iason_parse_number(p);
+  iason_die("IASON_LEGE: unexpected character");
+  return cent_null();
+}
+
+CentValue cent_iason_lege(CentValue s, int fractio_loaded) {
+  if (s.type != CENT_STR) cent_type_error("IASON_LEGE requires a string");
+  IasonParser p = { s.sval, 0, strlen(s.sval), fractio_loaded };
+  CentValue v = iason_parse_value(&p);
+  iason_skip_ws(&p);
+  if (p.pos != p.len) iason_die("IASON_LEGE: trailing data after JSON value");
+  return v;
+}
+
+/* ---------- serializer --------------------------------------------- */
+
+typedef struct {
+  char  *buf;
+  size_t len;
+  size_t cap;
+} IasonBuf;
+
+static void iason_buf_reserve(IasonBuf *b, size_t extra) {
+  if (b->len + extra <= b->cap) return;
+  size_t new_cap = b->cap ? b->cap * 2 : 64;
+  while (new_cap < b->len + extra) new_cap *= 2;
+  char *nb = cent_arena_alloc(cent_arena, new_cap);
+  if (b->len) memcpy(nb, b->buf, b->len);
+  b->buf = nb;
+  b->cap = new_cap;
+}
+
+static void iason_buf_putc(IasonBuf *b, char c) {
+  iason_buf_reserve(b, 1);
+  b->buf[b->len++] = c;
+}
+
+static void iason_buf_puts(IasonBuf *b, const char *s) {
+  size_t n = strlen(s);
+  iason_buf_reserve(b, n);
+  memcpy(b->buf + b->len, s, n);
+  b->len += n;
+}
+
+static void iason_buf_putn(IasonBuf *b, const char *s, size_t n) {
+  iason_buf_reserve(b, n);
+  memcpy(b->buf + b->len, s, n);
+  b->len += n;
+}
+
+static void iason_emit_string(IasonBuf *b, const char *s) {
+  iason_buf_putc(b, '"');
+  for (const unsigned char *p = (const unsigned char *)s; *p; p++) {
+    unsigned char c = *p;
+    switch (c) {
+      case '"':  iason_buf_puts(b, "\\\""); break;
+      case '\\': iason_buf_puts(b, "\\\\"); break;
+      case '\b': iason_buf_puts(b, "\\b");  break;
+      case '\f': iason_buf_puts(b, "\\f");  break;
+      case '\n': iason_buf_puts(b, "\\n");  break;
+      case '\r': iason_buf_puts(b, "\\r");  break;
+      case '\t': iason_buf_puts(b, "\\t");  break;
+      default:
+        if (c < 0x20) {
+          char tmp[8];
+          snprintf(tmp, sizeof tmp, "\\u%04x", c);
+          iason_buf_puts(b, tmp);
+        } else {
+          iason_buf_putc(b, (char)c);
+        }
+    }
+  }
+  iason_buf_putc(b, '"');
+}
+
+static void iason_emit_value(IasonBuf *b, CentValue v) {
+  switch (v.type) {
+    case CENT_NULL: iason_buf_puts(b, "null"); return;
+    case CENT_BOOL: iason_buf_puts(b, v.bval ? "true" : "false"); return;
+    case CENT_INT: {
+      char tmp[32];
+      int n = snprintf(tmp, sizeof tmp, "%ld", v.ival);
+      iason_buf_putn(b, tmp, (size_t)n);
+      return;
+    }
+    case CENT_FRAC: {
+      double d = (double)v.fval.num / (double)v.fval.den;
+      /* Shortest round-trippable representation, like Python's float repr. */
+      char tmp[64];
+      int n = 0;
+      for (int prec = 15; prec <= 17; prec++) {
+        n = snprintf(tmp, sizeof tmp, "%.*g", prec, d);
+        if (strtod(tmp, NULL) == d) break;
+      }
+      iason_buf_putn(b, tmp, (size_t)n);
+      return;
+    }
+    case CENT_STR:  iason_emit_string(b, v.sval); return;
+    case CENT_LIST: {
+      iason_buf_putc(b, '[');
+      for (int i = 0; i < v.lval.len; i++) {
+        if (i > 0) iason_buf_puts(b, ", ");
+        iason_emit_value(b, v.lval.items[i]);
+      }
+      iason_buf_putc(b, ']');
+      return;
+    }
+    case CENT_DICT: {
+      iason_buf_putc(b, '{');
+      for (int i = 0; i < v.dval.len; i++) {
+        if (i > 0) iason_buf_puts(b, ", ");
+        CentValue k = v.dval.keys[i];
+        if (k.type != CENT_STR)
+          cent_runtime_error("IASON_SCRIBE: dict keys must be strings to serialize as JSON");
+        iason_emit_string(b, k.sval);
+        iason_buf_puts(b, ": ");
+        iason_emit_value(b, v.dval.vals[i]);
+      }
+      iason_buf_putc(b, '}');
+      return;
+    }
+    case CENT_FUNC:
+      cent_runtime_error("IASON_SCRIBE: cannot serialize a function");
+      return;
+  }
+}
+
+CentValue cent_iason_scribe(CentValue v) {
+  IasonBuf b = { NULL, 0, 0 };
+  iason_emit_value(&b, v);
+  iason_buf_putc(&b, '\0');
+  return cent_str(b.buf);
+}
diff --git a/centvrion/compiler/runtime/cent_iason.h b/centvrion/compiler/runtime/cent_iason.h
new file mode 100644
index 0000000..7fc6123
--- /dev/null
+++ b/centvrion/compiler/runtime/cent_iason.h
@@ -0,0 +1,14 @@
+#ifndef CENT_IASON_H
+#define CENT_IASON_H
+
+#include "cent_runtime.h"
+
+/* IASON_LEGE — parse a JSON string into a CENTVRION value tree.
+   When fractio_loaded != 0, JSON floats become exact fractions; otherwise
+   they are floored to ints. */
+CentValue cent_iason_lege(CentValue s, int fractio_loaded);
+
+/* IASON_SCRIBE — serialize a CENTVRION value to a JSON string. */
+CentValue cent_iason_scribe(CentValue v);
+
+#endif /* CENT_IASON_H */
diff --git a/centvrion/lexer.py b/centvrion/lexer.py
index 0e68727..914e438 100644
--- a/centvrion/lexer.py
+++ b/centvrion/lexer.py
@@ -80,7 +80,9 @@ builtin_tokens = [("BUILTIN", i) for i in [
   "SCINDE",
   "PETE",
   "PETITVR",
-  "AVSCVLTA"
+  "AVSCVLTA",
+  "IASON_LEGE",
+  "IASON_SCRIBE"
 ]]
 
 data_tokens = [
@@ -92,6 +94,7 @@ data_tokens = [
 module_tokens = [("MODULE", i) for i in [
   "FORS",
   "FRACTIO",
+  "IASON",
   "MAGNVM",
   "SCRIPTA",
   "SVBNVLLA",
diff --git a/language/main.tex b/language/main.tex
index d2051ec..5231778 100644
--- a/language/main.tex
+++ b/language/main.tex
@@ -104,7 +104,7 @@
 \newpage
 \begin{itemize}
   \item \textbf{newline}: \\ Newlines are combined, so a single newline is the same as multiple.
-  \item \textbf{module-name}: \\ Modules are flags given to the interpreter/compiler, to let it know you want to be using certain rules, functions, or features. Available modules: \texttt{FORS} (randomness), \texttt{FRACTIO} (fractions), \texttt{MAGNVM} (large integers), \texttt{SCRIPTA} (file I/O: \texttt{LEGE}, \texttt{SCRIBE}, \texttt{ADIVNGE}), \texttt{SVBNVLLA} (negative literals), \texttt{RETE} (networking: \texttt{PETE}, \texttt{PETITVR}, \texttt{AVSCVLTA}).
+  \item \textbf{module-name}: \\ Modules are flags given to the interpreter/compiler, to let it know you want to be using certain rules, functions, or features. Available modules: \texttt{FORS} (randomness), \texttt{FRACTIO} (fractions), \texttt{IASON} (JSON I/O: \texttt{IASON\_LEGE}, \texttt{IASON\_SCRIBE}), \texttt{MAGNVM} (large integers), \texttt{SCRIPTA} (file I/O: \texttt{LEGE}, \texttt{SCRIBE}, \texttt{ADIVNGE}), \texttt{SVBNVLLA} (negative literals), \texttt{RETE} (networking: \texttt{PETE}, \texttt{PETITVR}, \texttt{AVSCVLTA}).
   \item \textbf{id}: \\ Variable. Can only consist of lowercase characters and underscores, but not the letters j, u, or w.
   \item \textbf{builtin}: \\ Builtin functions are uppercase latin words.
   \item \textbf{string}: \\ Any text encased in \texttt{"} or \texttt{'} characters. Single-quoted strings are always literal. Strings support 1-based indexing (\texttt{string[I]}) and inclusive slicing (\texttt{string[I VSQVE III]}), returning single-character strings and substrings respectively.
diff --git a/snippets/iason.cent b/snippets/iason.cent
new file mode 100644
index 0000000..b754f3d
--- /dev/null
+++ b/snippets/iason.cent
@@ -0,0 +1 @@
+CVM IASON
diff --git a/snippets/iason.png b/snippets/iason.png
new file mode 100644
index 0000000..56ed2bb
Binary files /dev/null and b/snippets/iason.png differ
diff --git a/snippets/iason_lege.cent b/snippets/iason_lege.cent
new file mode 100644
index 0000000..a712d13
--- /dev/null
+++ b/snippets/iason_lege.cent
@@ -0,0 +1,5 @@
+CVM IASON
+DESIGNA data VT IASON_LEGE('{"nomen": "Marcus", "anni": 30, "armorum": ["gladius", "scutum"]}')
+DIC(data["nomen"])
+DIC(data["anni"])
+DIC(data["armorum"])
diff --git a/snippets/iason_lege.png b/snippets/iason_lege.png
new file mode 100644
index 0000000..2e4dcf0
Binary files /dev/null and b/snippets/iason_lege.png differ
diff --git a/snippets/iason_scribe.cent b/snippets/iason_scribe.cent
new file mode 100644
index 0000000..55ee2b8
--- /dev/null
+++ b/snippets/iason_scribe.cent
@@ -0,0 +1,3 @@
+CVM IASON
+DESIGNA persona VT TABVLA {"nomen" VT "Marcus", "anni" VT XXX}
+DIC(IASON_SCRIBE(persona))
diff --git a/snippets/iason_scribe.png b/snippets/iason_scribe.png
new file mode 100644
index 0000000..f958a2b
Binary files /dev/null and b/snippets/iason_scribe.png differ
diff --git a/snippets/syntaxes/centvrion.sublime-syntax b/snippets/syntaxes/centvrion.sublime-syntax
index d2cfe32..2fecc8d 100644
--- a/snippets/syntaxes/centvrion.sublime-syntax
+++ b/snippets/syntaxes/centvrion.sublime-syntax
@@ -70,11 +70,11 @@ contexts:
       scope: constant.language.centvrion
 
   builtins:
-    - match: '\b(ADDE|ADIVNGE|AVDI_NVMERVS|AVDI|AVSCVLTA|CLAVES|CONFLA|CRIBRA|DECIMATIO|DIC|DORMI|EVERRE|FORTVITVS_NVMERVS|FORTVITA_ELECTIO|INSERE|IVNGE|LEGE|LITTERA|LONGITVDO|MAIVSCVLA|MINVSCVLA|MVTA|NECTE|NVMERVS|ORDINA|PETE|PETITVR|QVAERE|SCINDE|SCRIBE|SEMEN|SENATVS|SVBSTITVE|TOLLE|TYPVS)\b'
+    - match: '\b(ADDE|ADIVNGE|AVDI_NVMERVS|AVDI|AVSCVLTA|CLAVES|CONFLA|CRIBRA|DECIMATIO|DIC|DORMI|EVERRE|FORTVITVS_NVMERVS|FORTVITA_ELECTIO|IASON_LEGE|IASON_SCRIBE|INSERE|IVNGE|LEGE|LITTERA|LONGITVDO|MAIVSCVLA|MINVSCVLA|MVTA|NECTE|NVMERVS|ORDINA|PETE|PETITVR|QVAERE|SCINDE|SCRIBE|SEMEN|SENATVS|SVBSTITVE|TOLLE|TYPVS)\b'
       scope: support.function.builtin.centvrion
 
   modules:
-    - match: '\b(FORS|FRACTIO|MAGNVM|RETE|SCRIPTA|SVBNVLLA)\b'
+    - match: '\b(FORS|FRACTIO|IASON|MAGNVM|RETE|SCRIPTA|SVBNVLLA)\b'
       scope: support.class.module.centvrion
 
   keywords:
diff --git a/tests/12_test_failures.py b/tests/12_test_failures.py
index 7d55b79..53bfba0 100644
--- a/tests/12_test_failures.py
+++ b/tests/12_test_failures.py
@@ -8,7 +8,7 @@ from tests._helpers import (
   String, TemptaStatement, UnaryMinus, UnaryNot, Fractio, frac_to_fraction,
   fraction_to_frac, num_to_int, int_to_num, make_string,
   ValInt, ValStr, ValBool, ValList, ValDict, ValNul, ValFunc, ValFrac,
-  CentvrionError, _RUNTIME_C, _cent_rng,
+  CentvrionError, _RUNTIME_C, _IASON_C, _cent_rng,
   Lexer, Parser, compile_program,
   os, subprocess, tempfile, StringIO, patch,
 )
@@ -160,6 +160,24 @@ error_tests = [
   ('IVNGE(["a"], II)', CentvrionError),                                   # IVNGE second arg not a list
   ("IVNGE([VERITAS], [I])", CentvrionError),                              # IVNGE invalid key type (bool)
   ("IVNGE([[I]], [II])", CentvrionError),                                 # IVNGE invalid key type (list)
+  ("IASON_LEGE('null')", CentvrionError),                                 # IASON module required for IASON_LEGE
+  ("IASON_SCRIBE(NVLLVS)", CentvrionError),                               # IASON module required for IASON_SCRIBE
+  ("CVM IASON\nIASON_LEGE(I)", CentvrionError),                           # IASON_LEGE non-string arg
+  ("CVM IASON\nIASON_LEGE()", CentvrionError),                            # IASON_LEGE no args
+  ("CVM IASON\nIASON_LEGE('null', 'null')", CentvrionError),              # IASON_LEGE too many args
+  ("CVM IASON\nIASON_LEGE('not json')", CentvrionError),                  # invalid JSON
+  ("CVM IASON\nIASON_LEGE('[1,]')", CentvrionError),                      # trailing comma in array
+  ("CVM IASON\nIASON_LEGE('{\"a\":}')", CentvrionError),                  # missing value in object
+  ("CVM IASON\nIASON_LEGE('{\"a\" 1}')", CentvrionError),                 # missing colon in object
+  ("CVM IASON\nIASON_LEGE('[1, 2')", CentvrionError),                     # unterminated array
+  ("CVM IASON\nIASON_LEGE('{')", CentvrionError),                         # unterminated object
+  ("CVM IASON\nIASON_LEGE('\"abc')", CentvrionError),                     # unterminated string
+  ("CVM IASON\nIASON_LEGE('[1] junk')", CentvrionError),                  # trailing data
+  ("CVM IASON\nIASON_LEGE('[\"a\\\\x\"]')", CentvrionError),              # invalid escape
+  ("CVM IASON\nIASON_SCRIBE()", CentvrionError),                          # IASON_SCRIBE no args
+  ("CVM IASON\nIASON_SCRIBE(I, II)", CentvrionError),                     # IASON_SCRIBE too many args
+  ('CVM IASON\nIASON_SCRIBE(IVNGE([I], ["v"]))', CentvrionError),         # IASON_SCRIBE int dict keys
+  ("CVM IASON\nIASON_SCRIBE(FVNCTIO (x) VT { REDI(x) })", CentvrionError), # IASON_SCRIBE function
 ]
 
 class TestErrors(unittest.TestCase):
@@ -196,7 +214,7 @@ class TestErrorLineNumbers(unittest.TestCase):
       tmp_bin_path = tmp_bin.name
     try:
       subprocess.run(
-        ["gcc", "-O2", tmp_c_path, _RUNTIME_C, "-o", tmp_bin_path, "-lcurl", "-lmicrohttpd"],
+        ["gcc", "-O2", tmp_c_path, _RUNTIME_C, _IASON_C, "-o", tmp_bin_path, "-lcurl", "-lmicrohttpd", "-lm"],
         check=True, capture_output=True,
       )
       proc = subprocess.run([tmp_bin_path], capture_output=True, text=True)
diff --git a/tests/13_test_iason___.py b/tests/13_test_iason___.py
new file mode 100644
index 0000000..fe26198
--- /dev/null
+++ b/tests/13_test_iason___.py
@@ -0,0 +1,173 @@
+from tests._helpers import (
+  unittest, parameterized, Fraction,
+  run_test,
+  Bool, BuiltIn, DataArray, DataDict, Designa, ExpressionStatement, ID,
+  ModuleCall, Nullus, Numeral, Program, String,
+  ValInt, ValStr, ValBool, ValList, ValDict, ValNul, ValFrac,
+)
+
+
+def _scribe(arg, modules=("IASON",)):
+  return Program(
+    [ModuleCall(m) for m in modules],
+    [ExpressionStatement(BuiltIn("IASON_SCRIBE", [arg]))],
+  )
+
+def _lege(arg, modules=("IASON",)):
+  return Program(
+    [ModuleCall(m) for m in modules],
+    [ExpressionStatement(BuiltIn("IASON_LEGE", [String(arg)]))],
+  )
+
+def _src_lege(arg, extra_modules=()):
+  modules = ("IASON",) + tuple(extra_modules)
+  prefix = "\n".join(f"CVM {m}" for m in modules) + "\n"
+  return prefix + f"IASON_LEGE('{arg}')"
+
+def _src_scribe(arg_text, extra_modules=()):
+  modules = ("IASON",) + tuple(extra_modules)
+  prefix = "\n".join(f"CVM {m}" for m in modules) + "\n"
+  return prefix + f"IASON_SCRIBE({arg_text})"
+
+
+iason_tests = [
+  # ---- Parse: scalars ----
+  (_src_lege("null"),  _lege("null"),  ValNul()),
+  (_src_lege("true"),  _lege("true"),  ValBool(True)),
+  (_src_lege("false"), _lege("false"), ValBool(False)),
+  (_src_lege("42"),    _lege("42"),    ValInt(42)),
+  (_src_lege('"hello"'), _lege('"hello"'), ValStr("hello")),
+
+  # ---- Parse: empty containers ----
+  (_src_lege("[]"), _lege("[]"), ValList([])),
+  (_src_lege("{}"), _lege("{}"), ValDict({})),
+
+  # ---- Parse: array of mixed types ----
+  (_src_lege('[1, true, null, "x"]'),
+    _lege('[1, true, null, "x"]'),
+    ValList([ValInt(1), ValBool(True), ValNul(), ValStr("x")])),
+
+  # ---- Parse: nested ----
+  (_src_lege('{"a": [1, 2], "b": {"c": 3}}'),
+    _lege('{"a": [1, 2], "b": {"c": 3}}'),
+    ValDict({
+      "a": ValList([ValInt(1), ValInt(2)]),
+      "b": ValDict({"c": ValInt(3)}),
+    })),
+
+  # ---- Parse: numbers ----
+  (_src_lege("-7"), _lege("-7"), ValInt(-7)),
+  (_src_lege("0"),  _lege("0"),  ValInt(0)),
+
+  # ---- Parse: string escapes ----
+  # NB: single-quoted CENTVRION strings unescape \n / \" / \\ before the
+  # JSON parser sees them, so direct parse tests for those escapes would
+  # have ambiguous semantics. Serialize tests below cover the inverse, and
+  # this \u test exercises the JSON parser's escape path.
+  (_src_lege('"\\u00e9"'),
+    _lege('"\\u00e9"'),
+    ValStr("é")),
+
+  # ---- Parse: float without FRACTIO floors ----
+  (_src_lege("3.7"),  _lege("3.7"),  ValInt(3)),
+  (_src_lege("-2.5"), _lege("-2.5"), ValInt(-3)),
+  (_src_lege("1e2"),  _lege("1e2"),  ValInt(100)),
+
+  # ---- Parse: float with FRACTIO is exact ----
+  (_src_lege("0.5", extra_modules=("FRACTIO",)),
+    _lege("0.5", modules=("IASON", "FRACTIO")),
+    ValFrac(Fraction(1, 2))),
+  (_src_lege("0.1", extra_modules=("FRACTIO",)),
+    _lege("0.1", modules=("IASON", "FRACTIO")),
+    ValFrac(Fraction(1, 10))),
+  (_src_lege("-0.25", extra_modules=("FRACTIO",)),
+    _lege("-0.25", modules=("IASON", "FRACTIO")),
+    ValFrac(Fraction(-1, 4))),
+  (_src_lege("5", extra_modules=("FRACTIO",)),
+    _lege("5", modules=("IASON", "FRACTIO")),
+    ValInt(5)),
+  (_src_lege("3.0", extra_modules=("FRACTIO",)),
+    _lege("3.0", modules=("IASON", "FRACTIO")),
+    ValInt(3)),
+
+  # ---- Serialize: scalars ----
+  (_src_scribe("NVLLVS"),   _scribe(Nullus()),     ValStr("null")),
+  (_src_scribe("VERITAS"),  _scribe(Bool(True)),   ValStr("true")),
+  (_src_scribe("FALSITAS"), _scribe(Bool(False)),  ValStr("false")),
+  (_src_scribe("XLII"),     _scribe(Numeral("XLII")), ValStr("42")),
+  (_src_scribe('"hello"'),  _scribe(String("hello")), ValStr('"hello"')),
+  (_src_scribe("[]"),       _scribe(DataArray([])),   ValStr("[]")),
+  (_src_scribe("TABVLA {}"), _scribe(DataDict([])),   ValStr("{}")),
+
+  # ---- Serialize: nested ----
+  (_src_scribe("[I, II, III]"),
+    _scribe(DataArray([Numeral("I"), Numeral("II"), Numeral("III")])),
+    ValStr("[1, 2, 3]")),
+  (_src_scribe('TABVLA {"a" VT I, "b" VT VERITAS}'),
+    _scribe(DataDict([(String("a"), Numeral("I")), (String("b"), Bool(True))])),
+    ValStr('{"a": 1, "b": true}')),
+
+  # ---- Serialize: special chars ----
+  (_src_scribe('"a\\nb"'),
+    _scribe(String("a\nb")),
+    ValStr('"a\\nb"')),
+  (_src_scribe('"a\\"b"'),
+    _scribe(String('a"b')),
+    ValStr('"a\\"b"')),
+  (_src_scribe('"a\\\\b"'),
+    _scribe(String("a\\b")),
+    ValStr('"a\\\\b"')),
+
+  # ---- Round-trip ----
+  ("CVM IASON\nDIC(IASON_LEGE('[1, 2, 3]'))",
+    Program([ModuleCall("IASON")], [ExpressionStatement(BuiltIn("DIC",
+      [BuiltIn("IASON_LEGE", [String("[1, 2, 3]")])]))]),
+    ValStr("[I II III]"), "[I II III]\n"),
+
+  ("CVM IASON\nDIC(IASON_SCRIBE(IASON_LEGE('{\"a\": [1, true, null]}')))",
+    Program([ModuleCall("IASON")], [ExpressionStatement(BuiltIn("DIC",
+      [BuiltIn("IASON_SCRIBE",
+        [BuiltIn("IASON_LEGE", [String('{"a": [1, true, null]}')])])]))]),
+    ValStr('{"a": [1, true, null]}'),
+    '{"a": [1, true, null]}\n'),
+
+  ("CVM IASON\nCVM FRACTIO\nDIC(IASON_SCRIBE(IASON_LEGE('0.5')))",
+    Program([ModuleCall("IASON"), ModuleCall("FRACTIO")],
+      [ExpressionStatement(BuiltIn("DIC",
+        [BuiltIn("IASON_SCRIBE",
+          [BuiltIn("IASON_LEGE", [String("0.5")])])]))]),
+    ValStr("0.5"), "0.5\n"),
+
+  ("CVM IASON\nCVM FRACTIO\nDIC(IASON_SCRIBE(IASON_LEGE('0.1')))",
+    Program([ModuleCall("IASON"), ModuleCall("FRACTIO")],
+      [ExpressionStatement(BuiltIn("DIC",
+        [BuiltIn("IASON_SCRIBE",
+          [BuiltIn("IASON_LEGE", [String("0.1")])])]))]),
+    ValStr("0.1"), "0.1\n"),
+
+  # ---- Serialize: insertion order preserved ----
+  (_src_scribe('TABVLA {"b" VT II, "a" VT I, "c" VT III}'),
+    _scribe(DataDict([
+      (String("b"), Numeral("II")),
+      (String("a"), Numeral("I")),
+      (String("c"), Numeral("III")),
+    ])),
+    ValStr('{"b": 2, "a": 1, "c": 3}')),
+
+  # ---- Whitespace-tolerant parse ----
+  (_src_lege("  [  1  ,  2  ]  "),
+    _lege("  [  1  ,  2  ]  "),
+    ValList([ValInt(1), ValInt(2)])),
+
+  # ---- Unicode passes through serialize (ensure_ascii=False) ----
+  ('CVM IASON\nDIC(IASON_SCRIBE("café"))',
+    Program([ModuleCall("IASON")], [ExpressionStatement(BuiltIn("DIC",
+      [BuiltIn("IASON_SCRIBE", [String("café")])]))]),
+    ValStr('"café"'), '"café"\n'),
+]
+
+
+class TestIason(unittest.TestCase):
+  @parameterized.expand(iason_tests)
+  def test_iason(self, source, nodes, value, output="", input_lines=[]):
+    run_test(self, source, nodes, value, output, input_lines)
diff --git a/tests/_helpers.py b/tests/_helpers.py
index 417f696..23ba73d 100644
--- a/tests/_helpers.py
+++ b/tests/_helpers.py
@@ -24,10 +24,12 @@ from centvrion.lexer import Lexer
 from centvrion.parser import Parser
 from centvrion.values import ValInt, ValStr, ValBool, ValList, ValDict, ValNul, ValFunc, ValFrac
 
-_RUNTIME_C = os.path.join(
+_RUNTIME_DIR = os.path.join(
   os.path.dirname(__file__), "..",
-  "centvrion", "compiler", "runtime", "cent_runtime.c"
+  "centvrion", "compiler", "runtime"
 )
+_RUNTIME_C = os.path.join(_RUNTIME_DIR, "cent_runtime.c")
+_IASON_C = os.path.join(_RUNTIME_DIR, "cent_iason.c")
 
 def run_test(self, source, target_nodes, target_value, target_output="", input_lines=[]):
   _cent_rng.seed(1)
@@ -92,7 +94,7 @@ def run_test(self, source, target_nodes, target_value, target_output="", input_l
     tmp_bin_path = tmp_bin.name
   try:
     subprocess.run(
-      ["gcc", "-O2", tmp_c_path, _RUNTIME_C, "-o", tmp_bin_path, "-lcurl", "-lmicrohttpd"],
+      ["gcc", "-O2", tmp_c_path, _RUNTIME_C, _IASON_C, "-o", tmp_bin_path, "-lcurl", "-lmicrohttpd", "-lm"],
       check=True, capture_output=True,
     )
     stdin_data = "".join(f"{l}\n" for l in input_lines)
@@ -124,7 +126,7 @@ def run_compiler_error_test(self, source):
     tmp_bin_path = tmp_bin.name
   try:
     subprocess.run(
-      ["gcc", "-O2", tmp_c_path, _RUNTIME_C, "-o", tmp_bin_path, "-lcurl", "-lmicrohttpd"],
+      ["gcc", "-O2", tmp_c_path, _RUNTIME_C, _IASON_C, "-o", tmp_bin_path, "-lcurl", "-lmicrohttpd", "-lm"],
       check=True, capture_output=True,
     )
     proc = subprocess.run([tmp_bin_path], capture_output=True, text=True)
diff --git a/vscode-extension/syntaxes/cent.tmLanguage.json b/vscode-extension/syntaxes/cent.tmLanguage.json
index eea8ede..ead9e4c 100644
--- a/vscode-extension/syntaxes/cent.tmLanguage.json
+++ b/vscode-extension/syntaxes/cent.tmLanguage.json
@@ -65,7 +65,7 @@
 			"patterns": [
 				{
 					"name": "support.function.builtin.cent",
-					"match": "\\b(ADDE|ADIVNGE|AVDI_NVMERVS|AVDI|AVSCVLTA|CLAVES|CONFLA|CRIBRA|DECIMATIO|DIC|DORMI|EVERRE|FORTVITVS_NVMERVS|FORTVITA_ELECTIO|INSERE|IVNGE|LEGE|LITTERA|LONGITVDO|MAIVSCVLA|MINVSCVLA|MVTA|NECTE|NVMERVS|ORDINA|PETE|PETITVR|QVAERE|SCINDE|SCRIBE|SEMEN|SENATVS|SVBSTITVE|TOLLE|TYPVS)\\b"
+					"match": "\\b(ADDE|ADIVNGE|AVDI_NVMERVS|AVDI|AVSCVLTA|CLAVES|CONFLA|CRIBRA|DECIMATIO|DIC|DORMI|EVERRE|FORTVITVS_NVMERVS|FORTVITA_ELECTIO|IASON_LEGE|IASON_SCRIBE|INSERE|IVNGE|LEGE|LITTERA|LONGITVDO|MAIVSCVLA|MINVSCVLA|MVTA|NECTE|NVMERVS|ORDINA|PETE|PETITVR|QVAERE|SCINDE|SCRIBE|SEMEN|SENATVS|SVBSTITVE|TOLLE|TYPVS)\\b"
 				}
 			]
 		},
@@ -73,7 +73,7 @@
 			"patterns": [
 				{
 					"name": "support.class.module.cent",
-					"match": "\\b(FORS|FRACTIO|MAGNVM|RETE|SCRIPTA|SVBNVLLA)\\b"
+					"match": "\\b(FORS|FRACTIO|IASON|MAGNVM|RETE|SCRIPTA|SVBNVLLA)\\b"
 				}
 			]
 		},