# fastapi.online — Word Definition Lookup

> fastapi.online — Word Definition Lookup is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.0005/call, status unknown (last checked 2026-09-15).

Returns a definition for a given word, optionally contextualized by a provided context string, using self-hosted AI inference.

## Facts

- Endpoint: POST https://api.fastapi.online/define-word
- Price: $0.0005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastapi-online-word-definition-lookup-5a724014
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ragMAdv7TKkq4ltnGNS18

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-word-definition-lookup-5a724014 -d '<json body>'
```

Example prompt: What does the word 'sanguine' mean? Give me the definition — if it helps, use the context that I'm reading a Victorian-era novel.

## When to prefer this

Choose this endpoint when you need a quick, AI-generated word definition without requiring a dictionary API account or signup. Particularly useful when context-aware definitions are needed (e.g., domain-specific meanings), and when crypto micropayment per-call billing is preferred over subscription pricing. Ideal for agents needing lightweight, on-demand vocabulary lookups.

## Known failure modes

- Word field is empty or missing — validation error returned
- Word exceeds 100-character limit — request rejected
- Context exceeds 500-character limit — request rejected
- Ambiguous or nonsense input word — model may return a best-effort or fallback definition
- Payment not included or insufficient — 402 Payment Required response
- Model inference timeout or service unavailability — 5xx 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

A natural-language definition of the submitted word, potentially shaped by the optional context provided, generated by a self-hosted AI inference model.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "word": {
   "type": "string",
   "maxLength": 100,
   "minLength": 1
  },
  "context": {
   "type": "string",
   "maxLength": 500
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastapi-online-word-definition-lookup-5a724014/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)