# fastapi.online CEFR Level Estimator

> fastapi.online CEFR Level Estimator is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Estimates the CEFR language proficiency level (A1–C2) of a given text sample using AI inference

## Facts

- Endpoint: POST https://api.fastapi.online/cefr-level-estimate
- Price: $0.001/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-cefr-level-estimator-6f00d6e8
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_RZW6NjIXaNwjP0nh-YQ45

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-cefr-level-estimator-6f00d6e8 -d '<json body>'
```

Example prompt: Can you estimate the CEFR level of this paragraph I wrote: 'The government has implemented several measures to address the growing concerns regarding environmental sustainability, yet critics argue that these efforts remain insufficient given the scale of the crisis.'

## When to prefer this

Choose this endpoint when you need a lightweight, pay-per-call CEFR classification without committing to a subscription or signup. It is especially useful for edtech platforms, language learning apps, or content pipelines that need programmatic difficulty labeling of text. Prefer it over general-purpose LLM prompting when you want a structured, consistent CEFR output rather than a conversational language assessment.

## Known failure modes

- Text too short or too ambiguous to classify accurately, resulting in a low-confidence or fallback response
- Non-linguistic or code-heavy input may produce unreliable CEFR estimates
- Text exceeding 8000 characters will be rejected by the input schema
- Network or model inference errors may return a 500 or 402 payment-required response
- If the text is in a language other than English, results may be inaccurate or undefined

## 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 an estimated CEFR proficiency level (e.g. A1, A2, B1, B2, C1, or C2) for the submitted text, likely with a confidence score or explanation indicating why the text was placed at that level based on vocabulary, syntax complexity, and other linguistic features.

## 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-cefr-level-estimator-6f00d6e8/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)