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Readability Score API
x402
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.
Price / call$0.002
Success—
StatusUnknown
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.
Example use cases
Content grade-level check for educators
“I'm writing a science explainer aimed at 6th graders — can you run all the standard readability formulas on this passage and tell me if the grade level is appropriate? Here's the text: 'Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to produce oxygen and energy in the form of sugar.'”
Legal document simplification audit
“Before I send out this terms-of-service draft, can you calculate the Flesch Reading Ease, Flesch–Kincaid grade, and Gunning Fog scores for it so I can see how hard it is to read? Here's the text: 'The licensee hereby agrees to indemnify and hold harmless the licensor from any and all claims arising out of the licensee's use of the software.'”
Blog post readability optimization
“I want to see how readable my latest blog intro is — please give me all six readability scores including the sentence, word, and syllable counts for: 'Starting a business is one of the most exciting and challenging things you can do. Every day brings new problems to solve and opportunities to grow.'”
Technical details
Endpoint
POSThttps://readability.openverbs.com/v1/scoreWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object |
Tags
x402
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