# fastapi.online Reply Suggest

> fastapi.online Reply Suggest is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Generates multiple suggested reply options for a given message, useful for drafting conversational responses quickly.

## Facts

- Endpoint: POST https://api.fastapi.online/reply-suggest
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastapi-online-reply-suggest-b82df52f
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_2-4Cu-QexdB2z4TCeastC

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability fastapi-online-reply-suggest-b82df52f -d '<json body>'
```

Example prompt: Suggest 3 different replies I could send to this message: 'Hey, are you still interested in collaborating on the project? We'd love to have you on board!'

## When to prefer this

Choose this endpoint when you need multiple ready-to-use reply options for a single message — ideal for customer support automation, social media management, or any workflow where a human needs to quickly pick from pre-drafted responses. Prefer this over a generic chat endpoint when the goal is reply suggestion diversity rather than a single AI-generated answer.

## Known failure modes

- Message text is empty or missing — returns 400 validation error
- Count is out of range (below 1 or above 6) — returns 422 unprocessable entity
- Message exceeds 4000 characters — returns 422 validation error
- Payment not included or insufficient — returns 402 payment required
- Model inference timeout — may return 503 or timeout error

## How this service works

Chat, embeddings, OCR, speech-to-text, image editing, image understanding (captioning/Q&amp;A), text-to-speech, translation, writing tools, classification tools, developer tools, local utilities, format/checksum validators, encoding &amp; crypto utilities, date/time calculators, geo/coordinate math, math &amp; finance calculators, novelty tools, and business/social writing generators — 179 endpoints in all, across multiple specialized self-hosted models. Pay per call with crypto — no signup — or get an API key.

## Output

Returns a list of 1–6 suggested reply texts for the provided input message, each representing a distinct way to respond to that message. The agent can present these options to the user for selection or further editing.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "count": {
   "type": "integer",
   "maximum": 6,
   "minimum": 1
  },
  "message": {
   "type": "string",
   "maxLength": 4000,
   "minLength": 1
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastapi-online-reply-suggest-b82df52f/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.fastapi.online](https://www.zero.xyz/host/api.fastapi.online/llms.txt)