ctoon 0.3.0

A C++ TOON/JSON serialization library with Python bindings

CToon

The fastest implementation of the TOON format — a compact, human-readable serialisation format designed to minimise LLM token usage. Achieves 30–60% token reduction versus JSON while remaining fully readable and structured.

CToon is built on a high-performance C core and exposes the same logic through idiomatic bindings for C++, Python, and Go. The name reflects its foundation: C + TOON.

Format Overview

# JSON  (352 bytes)                  # TOON  (165 bytes, −53 %)
{                                    order:
  "order": {                           id: ORD-12345
    "id": "ORD-12345",                 status: completed
    "items": [                         customer:
      {"product":"Book","qty":2},        name: John Doe
      {"product":"Pen","qty":5}          email: [e-mail]
    ]                                  items[2]{product,qty}:
  }                                      Book,2
}                                        Pen,5

---

Quick Start

CLI

cmake -B build && cmake --build build
./build/ctoon data.json           # JSON  → TOON
./build/ctoon data.toon           # TOON  → JSON
cat data.json | ./build/ctoon     # stdin → TOON

C

#include "ctoon.h"

ctoon_doc *doc = ctoon_read("name: Alice\nage: 30", 20, 0);
ctoon_val *root = ctoon_doc_get_root(doc);

ctoon_val *name = ctoon_obj_get(root, "name");
printf("%s\n", ctoon_get_str(name));     /* Alice */

size_t len;
char *toon = ctoon_write(doc, &len);     /* caller must free() */
free(toon);
ctoon_doc_free(doc);

/* JSON output (requires CTOON_ENABLE_JSON=1, on by default) */
char *json = ctoon_doc_to_json(doc, 2, CTOON_WRITE_NOFLAG, NULL, &len, NULL);
free(json);

C++

#include "ctoon.hpp"

/* Parse TOON */
auto doc  = ctoon::document::parse("name: Alice\nage: 30");
auto root = doc.root();
std::cout << root["name"].get_str().str() << "\n";  // Alice
std::cout << root["age"].get_uint()        << "\n";  // 30

/* Serialise */
std::cout << doc.write().c_str()    << "\n";  // TOON
std::cout << doc.to_json(2).c_str() << "\n";  // JSON

/* Build a mutable document */
auto mdoc = ctoon::make_document();
auto obj  = mdoc.make_obj();
mdoc.set_root(obj);
obj.obj_put(mdoc.make_str("city"), mdoc.make_str("Tehran"));
obj.obj_put(mdoc.make_str("pop"),  mdoc.make_uint(9'000'000));
std::cout << mdoc.to_json(0).c_str() << "\n";  // {"city":"Tehran","pop":9000000}

/* Parse JSON */
auto jdoc = ctoon::document::from_json(R"({"x":1,"y":2})");
std::cout << jdoc.root()["x"].get_uint() << "\n";  // 1

/* Read / write flags */
using rf = ctoon::read_flag;
using wf = ctoon::write_flag;
auto doc2 = ctoon::document::parse(src, rf::ALLOW_COMMENTS | rf::ALLOW_BOM);
auto out  = doc2.write(
    ctoon::write_options()
        .with_flag(wf::LENGTH_MARKER | wf::NEWLINE_AT_END)
        .with_delimiter(ctoon::delimiter::PIPE)
        .with_indent(4));

Python

import ctoon

# encode / decode
toon = ctoon.dumps({"name": "Alice", "age": 30})
data = ctoon.loads(toon)

# file I/O — accepts path strings or file-like objects
ctoon.dump(data, "out.toon")
data = ctoon.load("out.toon")

with open("out.toon", "w") as f:
    ctoon.dump(data, f)

with open("out.toon") as f:
    data = ctoon.load(f)

# JSON
json_str = ctoon.dumps_json(data, indent=2)
data     = ctoon.loads_json(json_str)
ctoon.dump_json(data, "out.json")

# flags (combinable with |)
from ctoon import ReadFlag, WriteFlag, Delimiter
toon = ctoon.dumps(data,
                   indent=4,
                   delimiter=Delimiter.PIPE,
                   flags=WriteFlag.LENGTH_MARKER | WriteFlag.NEWLINE_AT_END)
data = ctoon.loads(toon, flags=ReadFlag.ALLOW_COMMENTS | ReadFlag.ALLOW_BOM)

Go

import ctoon "github.com/mohammadraziei/ctoon"

// encode / decode
toon, _ := ctoon.Dumps(map[string]interface{}{"name": "Alice", "age": int64(30)})
val,  _ := ctoon.Loads(toon)

// file I/O
ctoon.EncodeToFile(data, "out.toon", ctoon.DefaultEncodeOptions())
val, _ = ctoon.DecodeFromFile("out.toon", ctoon.DefaultDecodeOptions())

// JSON
json, _ := ctoon.DumpsJSON(data, 2)
val,  _ = ctoon.LoadsJSON(json)
ctoon.DumpJSON(data, "out.json")

---

Build

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j$(nproc) --target ctoon_test # Run C / C++ / python / Go tests
cmake --build build -j$(nproc) --target ctoon_coverage # Get the coverage of C / C++ / python / Go tests.

CMake options

Option	Default	Description
CTOON_BUILD_TESTS	ON	Build C and C++ tests
CTOON_BUILD_PYTHON	OFF	Build Python extension (nanobind)
CTOON_BUILD_DOCS	OFF	Build documents

JSON support is on by default (CTOON_ENABLE_JSON=1). The CLI uses it directly — no external JSON library required.

Python package

pip install ctoon # build and install

No runtime requirements.

Go module

go get github.com/mohammadraziei/ctoon

Requires Go 1.21+. Uses CGo to call the C core.

---

CLI Reference

# Encode  JSON → TOON
ctoon input.json
ctoon input.json -o output.toon
ctoon input.json --delimiter pipe      # comma (default), tab, pipe
ctoon input.json --length-marker       # items[#3]: …
ctoon input.json --stats               # show byte savings

# Decode  TOON → JSON
ctoon input.toon
ctoon input.toon -o output.json
ctoon input.toon -i 4                  # 4-space JSON indent

# Force format (auto-detected from extension by default)
ctoon -e input.json    # force encode
ctoon -d input.toon    # force decode

# Stdin
cat data.json | ctoon -e -
cat data.toon | ctoon -d -

---

C API Reference

Parsing

/* from memory */
ctoon_doc *ctoon_read(const char *toon, size_t len, ctoon_read_flag flags);
ctoon_doc *ctoon_read_opts(char *toon, size_t len, ctoon_read_flag flags,
                            const ctoon_alc *alc, ctoon_read_err *err);
/* from file */
ctoon_doc *ctoon_read_file(const char *path, ctoon_read_flag flags,
                            const ctoon_alc *alc, ctoon_read_err *err);
/* from JSON */
ctoon_doc *ctoon_read_json(char *json, size_t len, ctoon_read_flag flags,
                            const ctoon_alc *alc, ctoon_read_err *err);
ctoon_doc *ctoon_read_json_file(const char *path, ctoon_read_flag flags,
                                 const ctoon_alc *alc, ctoon_read_err *err);

Writing

/* TOON output */
char *ctoon_write(const ctoon_doc *doc, size_t *len);
char *ctoon_write_opts(const ctoon_doc *doc, const ctoon_write_options *opts,
                        const ctoon_alc *alc, size_t *len, ctoon_write_err *err);
char *ctoon_mut_write(const ctoon_mut_doc *doc, size_t *len);

/* JSON output */
char *ctoon_doc_to_json(const ctoon_doc *doc, int indent,
                         ctoon_write_flag flags, const ctoon_alc *alc,
                         size_t *len, ctoon_write_err *err);
char *ctoon_mut_doc_to_json(const ctoon_mut_doc *doc, int indent,
                              ctoon_write_flag flags, const ctoon_alc *alc,
                              size_t *len, ctoon_write_err *err);

Access

/* document */
ctoon_val *ctoon_doc_get_root(const ctoon_doc *doc);
void       ctoon_doc_free(ctoon_doc *doc);

/* type checks */
bool ctoon_is_null(ctoon_val *v);   bool ctoon_is_bool(ctoon_val *v);
bool ctoon_is_true(ctoon_val *v);   bool ctoon_is_false(ctoon_val *v);
bool ctoon_is_num(ctoon_val *v);    bool ctoon_is_uint(ctoon_val *v);
bool ctoon_is_sint(ctoon_val *v);   bool ctoon_is_real(ctoon_val *v);
bool ctoon_is_str(ctoon_val *v);    bool ctoon_is_arr(ctoon_val *v);
bool ctoon_is_obj(ctoon_val *v);

/* getters */
const char   *ctoon_get_str(ctoon_val *v);
uint64_t      ctoon_get_uint(ctoon_val *v);
int64_t       ctoon_get_sint(ctoon_val *v);
double        ctoon_get_real(ctoon_val *v);
bool          ctoon_get_bool(ctoon_val *v);
size_t        ctoon_get_len(ctoon_val *v);

/* array */
size_t     ctoon_arr_size(ctoon_val *arr);
ctoon_val *ctoon_arr_get(ctoon_val *arr, size_t idx);   /* O(1) */

/* object */
size_t     ctoon_obj_size(ctoon_val *obj);
ctoon_val *ctoon_obj_get(ctoon_val *obj, const char *key);

/* iteration */
ctoon_obj_iter ctoon_obj_iter_with(ctoon_val *obj);
ctoon_val     *ctoon_obj_iter_next(ctoon_obj_iter *iter);
ctoon_val     *ctoon_obj_iter_get_val(ctoon_val *key);

Mutable documents

ctoon_mut_doc *ctoon_mut_doc_new(const ctoon_alc *alc);
void           ctoon_mut_doc_free(ctoon_mut_doc *doc);
void           ctoon_mut_doc_set_root(ctoon_mut_doc *doc, ctoon_mut_val *root);

ctoon_mut_val *ctoon_mut_null(ctoon_mut_doc *doc);
ctoon_mut_val *ctoon_mut_bool(ctoon_mut_doc *doc, bool val);
ctoon_mut_val *ctoon_mut_uint(ctoon_mut_doc *doc, uint64_t val);
ctoon_mut_val *ctoon_mut_sint(ctoon_mut_doc *doc, int64_t val);
ctoon_mut_val *ctoon_mut_real(ctoon_mut_doc *doc, double val);
ctoon_mut_val *ctoon_mut_str(ctoon_mut_doc *doc, const char *str);
ctoon_mut_val *ctoon_mut_arr(ctoon_mut_doc *doc);
ctoon_mut_val *ctoon_mut_obj(ctoon_mut_doc *doc);

bool ctoon_mut_arr_append(ctoon_mut_val *arr, ctoon_mut_val *item);
bool ctoon_mut_obj_add(ctoon_mut_val *obj, ctoon_mut_val *key, ctoon_mut_val *val);
bool ctoon_mut_obj_put(ctoon_mut_val *obj, ctoon_mut_val *key, ctoon_mut_val *val);

/* convert between immutable and mutable */
ctoon_mut_doc *ctoon_doc_mut_copy(ctoon_doc *doc, const ctoon_alc *alc);
ctoon_doc     *ctoon_mut_doc_imut_copy(ctoon_mut_doc *doc, const ctoon_alc *alc);

---

Complexity

Operation	Time	Notes
ctoon_read / ctoon_read_json	O(n)	n = input bytes
ctoon_write / ctoon_doc_to_json	O(n)	zero extra copy for immutable doc
ctoon_mut_doc_to_json	O(n)	one imut_copy pass then serialise
ctoon_arr_get(arr, i)	O(1)	direct index into flat arena
ctoon_obj_get(obj, key)	O(k)	linear scan; k = key count
ctoon_doc_free	O(chunks) ≈ O(1)	arena freed in one shot
ctoon_doc_mut_copy	O(n)	deep copy

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Thread Safety

Scenario	Safe?
Multiple threads reading different documents	✅
Multiple threads reading the same document	✅
Building a document from multiple threads	❌ arena not thread-safe

---

Requirements

Component	Requirement
C core	C99, no dependencies
C++ binding	C++11, header-only
Python binding	Python 3.9+, nanobind ≥ 2.0, CMake 3.19+
Go binding	Go 1.21+, CGo
CLI	C++17

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License

MIT — see LICENSE.

Related

• toon-format/toon — the TOON format specification