# Readability Score API

> Readability Score API is a paid API for AI agents from readability.openverbs.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-14).

Computes six standard English readability formulas (Flesch Reading Ease, Flesch–Kincaid grade, Gunning Fog, SMOG, Coleman–Liau, ARI) plus underlying text statistics for a given text.

## Facts

- Endpoint: POST https://readability.openverbs.com/v1/score
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/readability-score-api-5842e784
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_cbOtZY0HOpxTo9N8gX9xm

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 readability-score-api-5842e784 -d '<json body>'
```

Example prompt: Can you run readability scores on this text and tell me the Flesch Reading Ease, Flesch–Kincaid grade, Gunning Fog, SMOG, Coleman–Liau, and ARI scores: 'The quick brown fox jumps over the lazy dog. Scientists have long debated the implications of this sentence for typographic testing.'

## When to prefer this

Choose this endpoint when you need multiple standard readability formula scores in a single call rather than querying them individually. It is ideal when you want a comprehensive readability audit — all six major indices plus raw text statistics — rather than a single consensus grade level (see the sibling consensus endpoint) or just syllable counts. Best suited for content QA pipelines, educational tools, writing assistants, or compliance checks where recognized formula names (Flesch, Gunning Fog, SMOG, ARI) must be reported.

## Known failure modes

- Empty text input returns HTTP 400 with a clean error response
- Extremely short text (single word) may produce unreliable formula scores
- Non-English text may yield inaccurate syllable counts and therefore skewed scores
- Very long texts may increase latency slightly but should still succeed

## How this service works

Compute the standard English readability formulas — Flesch Reading Ease, Flesch–Kincaid grade, Gunning fog, SMOG, Coleman–Liau and ARI — along with the underlying sentence/word/syllable statistics. Empty text is a clean 400.

## Output

Returns six readability formula scores (Flesch Reading Ease, Flesch–Kincaid Grade Level, Gunning Fog, SMOG, Coleman–Liau, ARI) along with underlying text statistics including sentence count, word count, and syllable count.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "text"
     ],
     "properties": {
      "text": {
       "type": "string",
       "description": "Text to analyse."
      }
     },
     "additionalProperties": false
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/readability-score-api-5842e784/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from readability.openverbs.com](https://www.zero.xyz/host/readability.openverbs.com/llms.txt)