# fastapi.online — Formality Classifier

> fastapi.online — Formality Classifier 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).

Classifies the formality level of a given text (e.g., formal vs. informal) using a self-hosted AI model.

## Facts

- Endpoint: POST https://api.fastapi.online/formality-classify
- 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-formality-classifier-9f423443
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_NOOceYqvkEH4Fx7bmFnk6

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-formality-classifier-9f423443 -d '<json body>'
```

Example prompt: Can you check whether this text sounds formal or informal: 'Hey, just wanted to touch base and see if you're free to grab coffee sometime soon'?

## When to prefer this

Use this endpoint when you need a lightweight, per-call formality classification of a text snippet without committing to a subscription or signup. Ideal for agents that need to audit or gate content based on register (formal vs. informal) as part of a writing pipeline, email assistant, or content moderation flow. At $0.0005 per call, it is cost-effective for high-volume classification tasks. Prefer over general-purpose LLM prompting when you want a dedicated, consistent classification signal rather than free-form judgment.

## Known failure modes

- Text field missing or empty — validation error returned
- Text exceeds 8000 character limit — request rejected
- Model inference failure — 500 error from self-hosted backend
- Payment not provided or insufficient — 402 Payment Required
- Ambiguous text may yield low-confidence classification

## 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 classification label indicating the formality level of the input text (e.g., 'formal', 'informal', or similar categories), likely accompanied by a confidence score or probability. The response tells the agent how formal or casual the provided text is judged to be.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "text": {
   "type": "string",
   "maxLength": 8000,
   "minLength": 1
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastapi-online-formality-classifier-9f423443/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)