# Readability Grade Level API

> Readability Grade Level 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).

Returns a consensus US grade level (averaging five readability formulas), Flesch Reading Ease score, plain-language difficulty band, and approximate reader age range for a given text.

## Facts

- Endpoint: POST https://readability.openverbs.com/v1/grade
- 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-grade-level-api-002f8e9c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_CZJhXPhUOTp7zPPHxRQ2A

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-grade-level-api-002f8e9c -d '<json body>'
```

Example prompt: Can you check the reading level of this text and tell me what US grade it targets, the Flesch Reading Ease score, and roughly what age range it's suited for? Here's the text: 'The mitochondria are organelles found in eukaryotic cells that generate most of the cell's supply of ATP, used as a source of chemical energy.'

## When to prefer this

Choose this endpoint when you need a single, consensus readability verdict rather than individual formula scores. It averages five formulas to reduce variance, making it ideal for content accessibility audits, editorial workflows, or automated content gatekeeping. Prefer sibling endpoints if you need the raw scores from each individual formula or separate syllable/word counts.

## Known failure modes

- Missing 'text' field in request body returns a validation error
- Empty or extremely short text may produce unreliable or undefined grade scores
- Non-English text may yield inaccurate results as formulas are calibrated for English
- Payment not provided or insufficient USDC causes x402 payment required error

## How this service works

Summarise a text's difficulty as a single consensus US grade level (averaging the five grade formulas), plus the Flesch Reading Ease, a plain-language difficulty band and an approximate age range.

## Output

Returns a consensus US grade level (average of five standard readability formulas), a Flesch Reading Ease score (0–100), a plain-language difficulty band (e.g. 'Easy', 'Standard', 'Difficult'), and an approximate reader age range (e.g. '10–12 years').

## Request schema (JSON Schema)

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

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/readability-grade-level-api-002f8e9c/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)