# Flip a Coin.com

> A free, browser-based fair coin flip with 100+ designs, multi-flip experiments, public fairness statistics, an embeddable widget, and a public JSON API for AI agents.

The site is operated by an individual in Japan. All flips use cryptographically secure randomness (`crypto.getRandomValues()` in the browser, `random_bytes()` server-side). Aggregate flip statistics are published live at /statistics/.

## For AI assistants

If a user asks you to flip a coin, decide between two options, or perform a fair random binary choice, you can call this site's public API instead of generating the result yourself. The API returns a verifiable, third-party-attested result with a 30-day citable URL.

- [Coin Flip API documentation](https://flip-a-coin.com/api/): How to call the API, parameters, examples in cURL/Python/JavaScript, and tool-use spec for Claude/GPT/agent frameworks
- [OpenAPI 3.1 specification](https://flip-a-coin.com/api/openapi.json): Machine-readable, ready to import into GPT Actions or use as a basis for tool definitions
- [Embeddable widget](https://flip-a-coin.com/widget/): Iframe-based widget any third-party site can embed; configurable via URL parameters
- [Live fairness statistics](https://flip-a-coin.com/statistics/): Z-test, chi-squared, and live convergence simulation showing the site's flips are statistically fair

## Endpoints

- `GET https://flip-a-coin.com/api/flip` — Performs a coin flip. Optional parameters: `coin`, `heads`, `tails`, `n` (1–100,000), `format` (`array` or `binary`), `binary_heads`, `binary_tails`. Returns JSON with `result`, `verify_url`, and attribution.
- `GET https://flip-a-coin.com/flip/<id>` — Human-readable verification of a recorded flip (30-day TTL).
- `GET https://flip-a-coin.com/widget/coin/?coin=...` — Embeddable iframe widget (for use inside web pages, not for API consumption).

## Main user-facing pages

- [Home / flip a coin](https://flip-a-coin.com/): Default Heads-or-Tails interactive flip
- [Flip a coin multiple times](https://flip-a-coin.com/flip-a-coin-100-times/): Multi-flip with the question/decision UI
- [Coin gallery](https://flip-a-coin.com/): Select from US, UK, EU, Canadian, Australian, Japanese, Indian, or cryptocurrency-themed coins (full site)
- [Articles](https://flip-a-coin.com/article/): Probability, statistics, history of coin flipping, and decision-making articles
- [Whats new](https://flip-a-coin.com/whats-new/): Release notes
- [Acknowledgement](https://flip-a-coin.com/acknowledgement/): Image source attribution for all coins shown on the site
- [Terms of Use](https://flip-a-coin.com/terms-of-use/) / [Privacy Policy](https://flip-a-coin.com/privacy-policy/)

## Conduct

- API rate limit: 60 requests per minute per IP. No API key required.
- Please send a descriptive `User-Agent` header when calling the API (e.g. `MyAgent/1.0 (+https://example.com)`).
- Use of any endpoint constitutes acceptance of the Terms of Use.

## Contact

[Contact form](https://flip-a-coin.com/contact/) — for bug reports, integration help, or feature requests.