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Readability Grade Level API
x402
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.
Price / call$0.002
Success—
StatusUnknown
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').
Example use cases
Checking blog post accessibility
“I just wrote this blog post intro and want to know if it's accessible to a general adult audience — can you get me the grade level, reading ease score, and difficulty band? Here's the text: 'Climate change is accelerating at an unprecedented rate, driven by anthropogenic greenhouse gas emissions that are fundamentally altering the planet's atmospheric composition.'”
Educational content grading
“I'm writing a worksheet for 5th graders and need to check if this paragraph is at the right level — what US grade level does it score, and what age range does it suit? Text: 'Plants make their own food using sunlight, water, and carbon dioxide in a process called photosynthesis. The green color in leaves comes from a chemical called chlorophyll.'”
Legal document readability audit
“Can you run a readability grade check on this contract clause and tell me the consensus grade level, Flesch Reading Ease, and difficulty band? Clause: 'The indemnifying party shall defend, indemnify, and hold harmless the indemnified party from and against any and all claims, damages, losses, costs, and expenses arising out of or relating to any breach of this Agreement.'”
Technical details
Endpoint
POSThttps://readability.openverbs.com/v1/gradeWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object |
Tags
x402
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