# Coin Flips — Randomly

> Biased or fair, showing the longest run against the expected log₂ n. One of 63 generators at [Randomly](https://randomly.cluxnei.dev), a library of random generators seeded from verifiable real-world entropy. Free HTTP API, no key, no signup.

## `numbers.coin` — Coin Flips

Biased or fair, showing the longest run against the expected log₂ n.

| | |
|---|---|
| **Key** | `numbers.coin` |
| **Module** | `numbers` |
| **Version** | `1` — a permalink carries this, and a replay against a different version returns `409` rather than something else |
| **Formats** | `application/json`, `text/plain` |
| **Studio** | https://randomly.cluxnei.dev/g/numbers/coin |
| **API** | `GET https://randomly.cluxnei.dev/api/v1/g/numbers.coin` |

`value` is the result itself — one value, or a list of them; `display` is the same thing rendered as a single human-readable string.

| Parameter | Type | Default | Accepts | What it does |
|---|---|---|---|---|
| `count` | int | `100` | `1` – `10000` | Flips |
| `bias` | float | `0.5` | `0` – `1` | P(heads) — A fair coin is 0.5. Bias it and watch the longest run of heads grow much faster than the head count does. |
| `style` | enum | `ht` | `ht`, `words`, `binary`, `circles` | Faces |
| `group` | int | `10` | `0` – `50` | Group every — Insert a space every n flips so the sequence can be read. Zero runs them together. |

Out-of-range numbers are **clamped, not rejected**, so a request never fails for being
ambitious — but it may not do what you meant. Unknown keys are dropped and missing ones
fall back to the defaults above.

```bash
curl -s 'https://randomly.cluxnei.dev/api/v1/g/numbers.coin?count=100&bias=0.5&style=ht' -H 'Accept: text/plain'
```

## The receipt

Every result carries one, naming the physical source of the randomness and linking to the
third party's own record of it:

```json
"receipt": {
  "source": "seismic",
  "source_label": "USGS Seismic Feed",
  "class": "C",
  "caveat": "Carries only tens of bits of genuine surprise. Always mixed with the OS CSPRNG.",
  "narrative": "A magnitude 3.6 earthquake, 67 km N of Culebra, Puerto Rico, 39.6 km down — 52 minutes ago.",
  "proof_url": "https://earthquake.usgs.gov/earthquakes/eventpage/us7000th33",
  "mixed_with_csprng": true,
  "degraded": false
}
```

Pick the source with `?source=`, or leave it at the default `auto`:

- **Class A** (Cryptographic) — `csprng`, `anu-qrng`, `random-org`
- **Class B** (Public beacon) — `nist-beacon`, `drand`, `bitcoin`. Published openly — anyone can look this value up after the fact.
- **Class C** (Observational) — `seismic`, `space-weather`, `atmosphere`, `iss`. Carries only tens of bits of genuine surprise. Always mixed with the OS CSPRNG.

## More

- [The full API contract](https://randomly.cluxnei.dev/api.md)
- [Everything in one file](https://randomly.cluxnei.dev/llms-full.txt)
- [The catalogue as JSON](https://randomly.cluxnei.dev/api/v1/generators)
- [This generator in the browser](https://randomly.cluxnei.dev/g/numbers/coin)