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++, Go, Julia, MATLAB, Python, Rust, and Zig, plus a standalone CLI. 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: john@example.com
    ]                                  items[2]{product,qty}:
  }                                      Book,2
}                                        Pen,5

Quick Start

Pick your language below — each section is install, a short example, then a link to that language's full reference for everything else (flags, options, error handling, ...). Order matches the tabs on the documentation site.

CLI

pip install ctoon        # ships a pre-built `ctoon` binary — no compiler needed

ctoon input.json                 # JSON  -> TOON (auto-detected from extension)
ctoon input.toon -o output.json  # TOON  -> JSON
cat data.json | ctoon -e -       # stdin -> TOON

Building from source with CMake instead is also supported (sudo cmake --install build after building — see Building & Testing). → Full CLI reference

C

Requires CMake 3.19+ and a C99 compiler.

# CMakeLists.txt
include(FetchContent)
FetchContent_Declare(ctoon
  GIT_REPOSITORY https://github.com/MohammadRaziei/ctoon.git  GIT_TAG main)
FetchContent_MakeAvailable(ctoon)
target_link_libraries(my_app PRIVATE ctoon::ctoon)

#include "ctoon.h"

ctoon_doc *doc = ctoon_read("name: Alice\nage: 30", 20, 0);
ctoon_val *root = ctoon_doc_get_root(doc);
printf("%s\n", ctoon_get_str(ctoon_obj_get(root, "name")));  /* Alice */

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

→ Full C API reference (also summarised below)

C++

Requires CMake 3.19+ and a C++11 compiler. Header-only on top of the C core.

# same FetchContent block as C, then:
target_link_libraries(my_app PRIVATE ctoon::ctoonpp)

#include "ctoon.hpp"

auto doc  = ctoon::document::parse("name: Alice\nage: 30");
auto root = doc.root();
std::cout << root["name"].get_str().str() << "\n";  // Alice
std::cout << doc.to_json(2).c_str() << "\n";         // pretty JSON

→ Full C++ API reference

Go

Requires Go 1.21+ with CGo enabled; a C compiler must be on the build host.

go get github.com/mohammadraziei/ctoon

import ctoon "github.com/mohammadraziei/ctoon"

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

→ Full Go reference

Julia

Requires Julia 1.7+ and a C compiler. Not yet in Julia's General registry.

import Pkg
Pkg.add(url="https://github.com/mohammadraziei/ctoon.git", subdir="src/bindings/julia")

using CToon

data = CToon.parse("""{"name": "Alice", "age": 30}""")
println(data["name"])   # Alice

→ Full Julia reference

MATLAB

Requires MATLAB R2014b+ and a C compiler configured for MEX (mex -setup C).

cd src/bindings/matlab
ctoon_install    % compiles the MEX gateway, adds it to your MATLAB path

s = ctoon.encode(struct('name', 'Alice', 'age', uint64(30)));
v = ctoon.decode(s);
v.name    % 'Alice'

→ Full MATLAB reference (type mapping, ctoon.read/ctoon.write, Python-style aliases, ...)

Python

Requires Python 3.9+. Pre-built wheels for Linux, macOS and Windows — no compiler needed.

pip install ctoon

import ctoon

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

→ Full Python reference

Rust

Requires Rust 1.70+ and a C compiler on the build host.

[dependencies]
ctoon = { git = "https://github.com/mohammadraziei/ctoon.git" }

let val = ctoon::loads("name: Alice\nage: 30")?;
println!("{}", val["name"].as_str().unwrap()); // Alice
let toon = ctoon::dumps(&val)?;

→ Full Rust reference

Zig

Requires Zig 0.16.0+.

zig fetch --save git+https://github.com/mohammadraziei/ctoon.git

const ctoon = @import("ctoon");

var val = try ctoon.loads(gpa, "name: Alice\nage: 30");
defer val.deinit(gpa);
const toon = try ctoon.dumps(gpa, val);

→ Full Zig reference

Building & Testing From Source

Each binding can be built, run and tested entirely with its own native tooling — cargo test for Rust, go test for Go, pytest for Python, zig build test for Zig, Pkg.test() for Julia, MATLAB's buildtool test — pick whichever's already open and go. But the project as a whole — building every language together, running the full cross-language test matrix, generating coverage, and building the documentation site — is driven by CMake, the same commands CI uses. This section covers that path; see CONTRIBUTING.md for the complete contributor workflow.

Configure

cmake -B build -DCMAKE_BUILD_TYPE=Release

By default this configures only C, C++ and the CLI. Each other language is opt-in via its own flag — and the flag changes what a missing toolchain does: silently skipped when the flag is OFF (the default, so the command above works on a machine with only some toolchains installed), a hard configure error when you've explicitly turned it ON:

# e.g. working on the Rust binding
cmake -B build -DCMAKE_BUILD_TYPE=Release -DCTOON_BUILD_RUST=ON

# everything, like CI
cmake -B build -DCMAKE_BUILD_TYPE=Release \
      -DCTOON_BUILD_PYTHON=ON -DCTOON_BUILD_GO=ON -DCTOON_BUILD_RUST=ON \
      -DCTOON_BUILD_ZIG=ON -DCTOON_BUILD_JULIA=ON

CMake options

JSON support is on by default. Define CTOON_DISABLE_JSON to turn it off — no external JSON library is required either way.

Build

cmake --build build -j

Test

ctest --test-dir build --output-on-failure --extra-verbose
# equivalently:
cmake --build build --target ctoon_test

Per-language targets, for iterating on one binding at a time: ctoon_test_c, ctoon_test_cpp, ctoon_test_go, ctoon_test_julia, ctoon_test_matlab, ctoon_test_python, ctoon_test_rust, ctoon_test_zig — each also runnable as a single ctest case, e.g. ctest --test-dir build -R rust.

Coverage

cmake --build build --target ctoon_coverage

Per-language: ctoon_coverage_c, ctoon_coverage_cpp, ctoon_coverage_go, ctoon_coverage_julia, ctoon_coverage_matlab, ctoon_coverage_python, ctoon_coverage_rust, plus ctoon_coverage_total (merged C/C++/Python/Go/Rust/Julia lcov report). Output lands in build/coverage/, with build/coverage/index.html as the dashboard — published at mohammadraziei.github.io/ctoon/coverage. (Zig has no coverage target yet — see the comment in tests/zig/CMakeLists.txt.)

Docs

cmake -B build -DCTOON_BUILD_DOCS=ON   # plus any CTOON_BUILD_<LANG>=ON you need
cmake --build build --target ctoon_docs

Per-language: ctoon_docs_c, ctoon_docs_cpp, ctoon_docs_julia, ctoon_docs_matlab, ctoon_docs_python, ctoon_docs_rust, plus ctoon_docs_index for the landing page (CLI and Zig are assembled straight from Markdown, no external doc tool needed). Output lands in build/docs/out/.

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);
ctoon_doc *ctoon_read_opts_indent(char *toon, size_t len, ctoon_read_flag flags,
                                   int indent_size, 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);

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_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);

/* 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_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

Thread Safety

License

MIT — see LICENSE.

Related

• toon-format/toon — the TOON format specification