Readability Analysis

The /read endpoint analyzes a text and returns its word, sentence and syllable counts, its Flesch readability scores and an estimated reading time.

POST/v5/read

How it works?

English uses the original Flesch coefficients, which also give a Flesch-Kincaid grade level. French uses the Kandel & Moles adaptation, which has no grade-level counterpart, so fleschKincaidGrade is null.

Syllables are estimated with a per-language heuristic: groups of vowels, minus the silent trailing e (e or es in French), with a minimum of one syllable per word. Sentences are split on ., !, ? and …, and a text without any of them counts as a single sentence. Reading time is based on 200 words per minute.

Parameters

The request body must be JSON:

Parameter	Required	Description
text	Yes	Text to analyze, 50000 characters maximum
lang	No	Language of the text: en or fr. Default: en

Response Fields

Field	Type	Description
lang	string	Language used for the analysis
words	number	Number of words — tokens containing at least one letter or digit
sentences	number	Number of sentences, always at least 1
syllables	number	Estimated total number of syllables
fleschReadingEase	number	Flesch reading ease, rounded to 2 decimals — the higher, the easier to read
fleschKincaidGrade	number|null	Flesch-Kincaid grade level, rounded to 2 decimals — null when lang is fr
readingTime	string	Estimated reading time, in seconds below a minute (e.g. 45s, 3min)

Code Examples

curl -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "text": "The cat sat on the mat. It was happy.",
    "lang": "en"
  }' \
  "https://api.sylvain.sh/v5/read"

Try It

POSThttps://api.sylvain.sh/v5/read

text*

langSelect...enfr

Error Handling

If parameters are missing or invalid, the API will return an error:

Error Message	Description
Please provide a text	The text parameter is missing, empty, or contains no word
Text must be 50000 characters or fewer	The text exceeds the maximum length
Language must be one of: en, fr	The lang value is neither en nor fr