YouTube thumbnail size checker API

Check your thumbnail against YouTube's published requirements, see where the duration badge roughly covers it, and export a 16:9 copy, all without uploading the image.

• Endpoint: POST https://postboost.co/app/api/tools/youtube-thumbnail-size-checker (operationId checkYoutubeThumbnail)
• Web tool: postboost.co/tools/youtube-thumbnail-size-checker
• Token: optional (limits)
• MCP: tool check-youtube-thumbnail on https://postboost.co/mcp/tools

Request

Field	Type	Default	Description
width	integer		Image width in pixels.
height	integer		Image height in pixels.
file_size_bytes	integer		File size in bytes.
format	string		MIME type, e.g. image/png or image/jpeg.

Call it

curl

curl -X POST https://postboost.co/app/api/tools/youtube-thumbnail-size-checker \
  -H 'Content-Type: application/json' \
  -d '{"width":1280,"height":720,"file_size_bytes":921600,"format":"image/png"}'

Python

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

with ApiClient(Configuration()) as client:
    api = FreeToolsApi(client)
    result = api.check_youtube_thumbnail(FreeToolCheckYoutubeThumbnailRequest.from_dict({"width": 1280, "height": 720, "file_size_bytes": 921600, "format": "image/png"}))
    print(result.to_dict())

Node.js

import { FreeToolsApi } from 'postboost';

const api = new FreeToolsApi();
const { body } = await api.checkYoutubeThumbnail({ width: 1280, height: 720, fileSizeBytes: 921600, format: "image/png" });
console.log(body);

PHP

use PostBoostClient\Api\FreeToolsApi;
use PostBoostClient\Model\FreeToolCheckYoutubeThumbnailRequest;

$api = new FreeToolsApi(new GuzzleHttp\Client());
$result = $api->checkYoutubeThumbnail(new FreeToolCheckYoutubeThumbnailRequest(['width' => 1280, 'height' => 720, 'file_size_bytes' => 921600, 'format' => "image/png"]));
echo $result;

Go

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

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

var request postboost.FreeToolCheckYoutubeThumbnailRequest
if err := json.Unmarshal([]byte(`{"width":1280,"height":720,"file_size_bytes":921600,"format":"image/png"}`), &request); err != nil {
    panic(err)
}

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

Ruby

require 'postboost'

api = PostBoost::FreeToolsApi.new
result = api.check_youtube_thumbnail(PostBoost::FreeToolCheckYoutubeThumbnailRequest.new({ width: 1280, height: 720, file_size_bytes: 921600, format: "image/png" }))
puts result.to_hash

Java

import com.postboost.ApiClient;
import com.postboost.api.FreeToolsApi;
import com.postboost.model.FreeToolCheckYoutubeThumbnailRequest;
import com.postboost.model.FreeToolCheckYoutubeThumbnailResponse;

FreeToolsApi api = new FreeToolsApi(new ApiClient());
FreeToolCheckYoutubeThumbnailRequest request = FreeToolCheckYoutubeThumbnailRequest.fromJson("{\"width\":1280,\"height\":720,\"file_size_bytes\":921600,\"format\":\"image/png\"}");
FreeToolCheckYoutubeThumbnailResponse result = api.checkYoutubeThumbnail(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<FreeToolCheckYoutubeThumbnailRequest>(@"{""width"":1280,""height"":720,""file_size_bytes"":921600,""format"":""image/png""}");
var result = await api.CheckYoutubeThumbnailAsync(request);
Console.WriteLine(result.ToJson());

Rust

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

let config = Configuration::new();
let request: FreeToolCheckYoutubeThumbnailRequest = serde_json::from_str(r##"{"width":1280,"height":720,"file_size_bytes":921600,"format":"image/png"}"##)?;
let result = free_tools_api::check_youtube_thumbnail(&config, request).await?;
println!("{:?}", result);

CLI

echo '{"width":1280,"height":720,"file_size_bytes":921600,"format":"image/png"}' | ./postboost-cli --content-type application/json checkYoutubeThumbnail -

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

Response

{
    "ok": true,
    "checks": [
        {
            "key": "ratio",
            "label": "Aspect ratio",
            "status": "pass",
            "detail": "16:9, needs 16:9"
        },
        {
            "key": "width",
            "label": "Width",
            "status": "pass",
            "detail": "1280 px, needs at least 640 px"
        },
        {
            "key": "file_size",
            "label": "File size",
            "status": "pass",
            "detail": "0.88 MB, needs 2 MB or less"
        },
        {
            "key": "format",
            "label": "Format",
            "status": "pass",
            "detail": "PNG"
        }
    ]
}

With MCP

Connect https://postboost.co/mcp/tools (setup) and ask, for example: Check a YouTube thumbnail's ratio, width, file size and format against YouTube's requirements with the PostBoost check-youtube-thumbnail 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.