Post readability checker API

Paste a social post or caption. The checker scores it with the Flesch reading ease and Flesch-Kincaid grade formulas, lists sentences of more than 25 words and possible passive phrases, and suggests what to change. Hashtags, mentions, links and emoji are not counted as words.

• Endpoint: POST https://postboost.co/app/api/tools/post-readability-checker (operationId checkReadability)
• Web tool: postboost.co/tools/post-readability-checker
• Token: optional (limits)
• MCP: tool check-readability on https://postboost.co/mcp/tools

Request

Field	Type	Default	Description
text	string		The post text.
language	string	"en"	Language code. Only English (en) is scored; other languages return supported: false and no scores.

Call it

curl

curl -X POST https://postboost.co/app/api/tools/post-readability-checker \
  -H 'Content-Type: application/json' \
  -d '{"text":"The cat sat on the mat. 🐱 #cats"}'

Python

from postboost import ApiClient, Configuration
from postboost.api.free_tools_api import FreeToolsApi
from postboost.models import FreeToolCheckReadabilityRequest

with ApiClient(Configuration()) as client:
    api = FreeToolsApi(client)
    result = api.check_readability(FreeToolCheckReadabilityRequest.from_dict({"text": "The cat sat on the mat. 🐱 #cats"}))
    print(result.to_dict())

Node.js

import { FreeToolsApi } from 'postboost';

const api = new FreeToolsApi();
const { body } = await api.checkReadability({ text: "The cat sat on the mat. 🐱 #cats" });
console.log(body);

PHP

use PostBoostClient\Api\FreeToolsApi;
use PostBoostClient\Model\FreeToolCheckReadabilityRequest;

$api = new FreeToolsApi(new GuzzleHttp\Client());
$result = $api->checkReadability(new FreeToolCheckReadabilityRequest(['text' => "The cat sat on the mat. 🐱 #cats"]));
echo $result;

Go

import (
    "context"
    "encoding/json"
    "fmt"

    postboost "github.com/postboost-co/postboost-go"
)

var request postboost.FreeToolCheckReadabilityRequest
if err := json.Unmarshal([]byte(`{"text":"The cat sat on the mat. 🐱 #cats"}`), &request); err != nil {
    panic(err)
}

client := postboost.NewAPIClient(postboost.NewConfiguration())
result, _, err := client.FreeToolsAPI.CheckReadability(context.Background()).FreeToolCheckReadabilityRequest(request).Execute()
fmt.Println(result, err)

Ruby

require 'postboost'

api = PostBoost::FreeToolsApi.new
result = api.check_readability(PostBoost::FreeToolCheckReadabilityRequest.new({ text: "The cat sat on the mat. 🐱 #cats" }))
puts result.to_hash

Java

import com.postboost.ApiClient;
import com.postboost.api.FreeToolsApi;
import com.postboost.model.FreeToolCheckReadabilityRequest;
import com.postboost.model.FreeToolCheckReadabilityResponse;

FreeToolsApi api = new FreeToolsApi(new ApiClient());
FreeToolCheckReadabilityRequest request = FreeToolCheckReadabilityRequest.fromJson("{\"text\":\"The cat sat on the mat. 🐱 #cats\"}");
FreeToolCheckReadabilityResponse result = api.checkReadability(request);
System.out.println(result.toJson());

C#

using Newtonsoft.Json;
using PostBoost.Client.Api;
using PostBoost.Client.Client;
using PostBoost.Client.Model;

var api = new FreeToolsApi(new Configuration());
var request = JsonConvert.DeserializeObject<FreeToolCheckReadabilityRequest>(@"{""text"":""The cat sat on the mat. 🐱 #cats""}");
var result = await api.CheckReadabilityAsync(request);
Console.WriteLine(result.ToJson());

Rust

use postboost::apis::configuration::Configuration;
use postboost::apis::free_tools_api;
use postboost::models::FreeToolCheckReadabilityRequest;

let config = Configuration::new();
let request: FreeToolCheckReadabilityRequest = serde_json::from_str(r##"{"text":"The cat sat on the mat. 🐱 #cats"}"##)?;
let result = free_tools_api::check_readability(&config, request).await?;
println!("{:?}", result);

CLI

echo '{"text":"The cat sat on the mat. 🐱 #cats"}' | ./postboost-cli --content-type application/json checkReadability -

With a token, send Authorization: Bearer YOUR_API_TOKEN as a default header (how, per SDK).

Response

{
    "supported": true,
    "note": null,
    "flesch_reading_ease": 116.1,
    "flesch_kincaid_grade": -1.5,
    "sentences": 1,
    "words": 6,
    "syllables": 6,
    "avg_words_per_sentence": 6,
    "long_sentences": [],
    "passive_hints": 0,
    "emoji_count": 1,
    "hashtag_count": 1,
    "suggestions": []
}

With MCP

Connect https://postboost.co/mcp/tools (setup) and ask, for example: Check the readability of a post: Flesch scores, long sentences and passive hints with the PostBoost check-readability tool.

Errors

Status	When
401	The Authorization header holds an invalid token. Leave it out to call as a guest.
413	The JSON body is larger than 128 KB.
422	A field is invalid; the body lists the errors per field.
429	A limit is reached; see limits.