# Fidren

> Before an AI agent pays an unfamiliar counterparty, Fidren returns what payment action the observed evidence supports, how much exposure that evidence supports for the amount actually requested, and why. Advisory and read-only: Fidren never holds, transmits, settles, signs, escrows or intermediates funds. It returns an advisory decision; the caller’s own infrastructure enforces it.

## What it returns

A call to `POST /v1/decision` answers with, in the order
that matters for acting on it:

- `payment_action`
- `recommended_limit_cents`
- `requested_amount_cents`
- `amount_status`
- `confidence`
- `reasons`
- `evidence`

Same counterparty, same evidence, a different requested amount: potentially a different payment action. The amount is an input to the decision, not a filter applied to a fixed score.

## When to call it

- Before sending a payment to a counterparty address the agent has not paid before.
- Before raising the amount it is willing to send to a counterparty it has paid before.
- When a counterparty requests more than a previously approved exposure.

## Minimum request

```bash
curl -s -X POST https://api.fidren.net/v1/decision \
  -H 'content-type: application/json' \
  -d '{"address":"0xf1d0000000000000000000000000000000000001","chain":"base","amount_cents":5000,"currency":"USD"}'
```

No credential is needed for that call.

## Cost

- Free: 100 free decisions per day, per IP. None. No account, no API key, no card, no wallet. Every day at 00:00 UTC.
- Pay per decision: $0.01 USDC over x402 v2 on eip155:8453 (Base mainnet).
  Exhausting the free allowance returns `402` carrying the terms in `PAYMENT-REQUIRED`.

## Coverage

Observed settlement history is indexed on **base** (eip155:8453) only.
The request schema also accepts `polygon`, but no corpus
is observed there, so such an address answers from no history rather than from evidence.
No other chain is supported, and none is claimed.

## Failure semantics

- `402` — Payment required. Returned when the Free allowance is exhausted, or immediately when the caller asks to pay. Carries the x402 terms in PAYMENT-REQUIRED.
- `429` — Rate limited. Retry-After is delta-seconds, never an HTTP-date. Back off; do not retry immediately.
- `400` — The request was malformed. `error.details[].field` names the offending field. Do not retry unchanged.
- `503` — Fidren could not answer. There is no verdict to fall back on: a caller must apply its own policy for an unavailable adviser, and must not read the absence of a decision as approval.

## Docs

- [Developers](https://fidren.net/developers): integration guide, x402 handshake, response fields.
- [OpenAPI](https://api.fidren.net/openapi.json): the machine-readable contract for every endpoint.
- [Home](https://fidren.net): what Fidren is and what it refuses to do.

## Optional

- [Contact](https://fidren.net/contact): reach a person.