Captcha Solver API

Solves 3-digit BLS captcha images. Accepts multipart uploads or JSON with base64 images, authenticates via API key, returns index-keyed digit codes.

Base URL: https://captcha.mostaxdev.com
Auth: X-API-Key or apikey header
Billing: 1 token per image. Refunded on failure.

quick start

curl -X POST "https://captcha.mostaxdev.com/solve" \
  -H "X-API-Key: YOUR_API_KEY" \
  -F "images=@captcha_1.png" \
  -F "images=@captcha_2.png"

Authentication

Every request to /solve requires an API key in one of two headers:

headers

X-API-Key: YOUR_API_KEY
# or
apikey: YOUR_API_KEY

Tokens are charged per image, not per request. A request with 9 images costs 9 tokens. If the request fails before processing, tokens are refunded.

POST /solve

Primary endpoint. Solves one or more BLS captcha images.

Param	Type	Notes
images	`multipart/form-data`	One or more files under the `images` field
images	`application/json`	Object keyed by index: `{"0": "data:image/png;base64,..."}`

Multipart

curl

curl -X POST "https://captcha.mostaxdev.com/solve" \
  -H "X-API-Key: YOUR_API_KEY" \
  -F "images=@captcha_0.png" \
  -F "images=@captcha_1.png" \
  -F "images=@captcha_2.png"

JSON body

curl

curl -X POST "https://captcha.mostaxdev.com/solve" \
  -H "X-API-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "images": {
      "0": "data:image/png;base64,iVBORw0KGgoAAA...",
      "1": "data:image/png;base64,iVBORw0KGgoAAA...",
      "2": "data:image/png;base64,iVBORw0KGgoAAA..."
    }
  }'

Response

200 ok

{
  "solution": {
    "0": "123",
    "1": "456",
    "2": "789"
  }
}

Response keys are string indexes matching request order. Values are always 3-digit strings.

Errors

All errors return {"detail": "..."}.

400Malformed JSON, missing images, or no valid images supplied.

401Missing or invalid API key.

403Valid key but insufficient tokens.

415Unsupported content type.

500Internal server error.

503Solver busy. Retry.

Client Examples

python — multipart

import requests

resp = requests.post(
    "https://captcha.mostaxdev.com/solve",
    headers={"X-API-Key": "YOUR_API_KEY"},
    files=[
        ("images", ("0.png", open("0.png", "rb"), "image/png")),
        ("images", ("1.png", open("1.png", "rb"), "image/png")),
    ],
    timeout=60,
)
resp.raise_for_status()
print(resp.json()["solution"])

python — base64 json

import base64, requests

def encode(path):
    with open(path, "rb") as f:
        return "data:image/png;base64," + base64.b64encode(f.read()).decode()

resp = requests.post(
    "https://captcha.mostaxdev.com/solve",
    headers={
        "X-API-Key": "YOUR_API_KEY",
        "Content-Type": "application/json",
    },
    json={"images": {"0": encode("0.png"), "1": encode("1.png")}},
    timeout=60,
)
print(resp.json()["solution"])

javascript — fetch

const res = await fetch(
  "https://captcha.mostaxdev.com/solve",
  {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "X-API-Key": apiKey,
    },
    body: JSON.stringify({ images }),
  }
);
const { solution } = await res.json();

javascript — formdata

const form = new FormData();
for (const blob of imageBlobs) {
  form.append("images", blob, "captcha.png");
}

const res = await fetch(
  "https://captcha.mostaxdev.com/solve",
  {
    method: "POST",
    headers: { "X-API-Key": apiKey },
    body: form,
  }
);
const { solution } = await res.json();

c# — httpclient

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("X-API-Key", apiKey);

using var form = new MultipartFormDataContent();
foreach (var path in imagePaths)
{
    var bytes = File.ReadAllBytes(path);
    form.Add(new ByteArrayContent(bytes), "images", Path.GetFileName(path));
}

var res = await client.PostAsync(
    "https://captcha.mostaxdev.com/solve", form);
res.EnsureSuccessStatusCode();

var json = await res.Content.ReadFromJsonAsync<JsonElement>();
var solution = json.GetProperty("solution");

body := &bytes.Buffer{}
w := multipart.NewWriter(body)
for _, path := range imagePaths {
    f, _ := os.Open(path)
    part, _ := w.CreateFormFile("images", filepath.Base(path))
    io.Copy(part, f)
    f.Close()
}
w.Close()

req, _ := http.NewRequest("POST",
    "https://captcha.mostaxdev.com/solve", body)
req.Header.Set("Content-Type", w.FormDataContentType())
req.Header.Set("X-API-Key", apiKey)

resp, _ := http.DefaultClient.Do(req)
defer resp.Body.Close()

var result struct {
    Solution map[string]string `json:"solution"`
}
json.NewDecoder(resp.Body).Decode(&result)

php — curl

$ch = curl_init("https://captcha.mostaxdev.com/solve");
curl_setopt_array($ch, [
    CURLOPT_POST           => true,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER     => ["X-API-Key: $apiKey"],
    CURLOPT_POSTFIELDS     => [
        "images[0]" => new CURLFile("0.png", "image/png"),
        "images[1]" => new CURLFile("1.png", "image/png"),
    ],
]);

$response = curl_exec($ch);
curl_close($ch);

$solution = json_decode($response, true)["solution"];

ruby

require "net/http"
require "json"

uri  = URI("https://captcha.mostaxdev.com/solve")
form = Net::HTTP::Post.new(uri)
form["X-API-Key"] = api_key
form.set_form(
  image_paths.map { |p|
    ["images", File.open(p), { filename: File.basename(p) }]
  },
  "multipart/form-data"
)

res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h|
  h.request(form)
}
solution = JSON.parse(res.body)["solution"]