One endpoint. Two prompts.

Setup

Base URL and key.

# same client, same request shape — only the endpoint moves
export CAPTCHA_KRAKEN_API_KEY=ck_live_…
export VLLM_BASE_URL=https://api.captchakraken.com/v1

Important

This is a captcha model, not a general vision model.

Request

Solving a grid challenge.

Send the captcha screenshot as a data URL and the prompt as text, in that order, inside one user turn.

curl https://api.captchakraken.com/v1/chat/completions \
  -H "Authorization: Bearer $CAPTCHA_KRAKEN_API_KEY" \
  -H "Content-Type: application/json" \
  -H "x-ck-session: $(uuidgen)" \
  -d '{
    "model": "captcha",
    "messages": [
      {
        "role": "system",
        "content": "You are an expert captcha solver. Respond ONLY with the JSON action."
      },
      {
        "role": "user",
        "content": [
          { "type": "image_url",
            "image_url": { "url": "data:image/png;base64,<SCREENSHOT>" } },
          { "type": "text", "text": "<PROMPT — see below>" }
        ]
      }
    ],
    "temperature": 0,
    "max_tokens": 128,
    "chat_template_kwargs": { "enable_thinking": false }
  }'

The grid prompt, verbatim

Substitute the real grid size and the matching hint line — Separate images. for a 3×3 of distinct photos, Single large image split into tiles. for a 4×4 subdivided one.

Solve the captcha grid by choosing the cell numbers that match the description from the captcha image prompt.

Grid: 3x3 (9 cells)
Hint: Separate images. Select only clear matches.

If no tiles match the description (e.g., they have all been cleared or none were present), return an empty list for target_ids: [].

Return JSON Array: [list of cell numbers (1-9)]

From an OpenAI SDK

from openai import OpenAI

client = OpenAI(
    api_key=os.environ["CAPTCHA_KRAKEN_API_KEY"],
    base_url="https://api.captchakraken.com/v1",
)

response = client.chat.completions.create(
    model="captcha",
    messages=[...],                      # shape as above
    temperature=0,
    max_tokens=128,
    extra_headers={"x-ck-session": session_uuid},
)

The response is a normal chat completion

The answer arrives as JSON in the message content. Grid challenges return the cell numbers to click; click/drag challenges return labelled coordinates on a normalised 0–1000 scale.

{
  "choices": [
    { "message": { "role": "assistant", "content": "[6, 8]" } }
  ],
  "usage": { "prompt_tokens": 1102, "completion_tokens": 7 }
}

Headers

Two optional headers that affect your bill.

There is no header that sets the puzzle class. Pricing is derived from the prompt in the body, so a header cannot move a request into a cheaper bracket.

Errors

Branch on the code, never on the message.

Errors use OpenAI's envelope, so your SDK will parse them. The prose gets reworded; error.code does not.

A revoked key and an unknown key both return invalid_api_key. Telling the difference apart would confirm to an attacker which of their guesses was once real.

MCP

Managing the account from an agent.

The same account, driven from an MCP client. It signs you in through GitHub, mints and revokes keys, and reads back what you have spent.

# Claude Code, Claude Desktop, or any MCP client
claude mcp add captchakraken -- npx -y captchakraken-mcp

The token the MCP server holds manages the account — it cannot solve captchas, and an API key cannot manage the account. Two credentials, two blast radii. Revoke either from the dashboard.

Billing

$0.30 per 1,000 image responses.

You are billed per inference response — no subscription, no monthly minimum, no per-seat fee, and no charge at all for challenges that never reach the model.

Most image captchas are solved in 1–2 image inference requests, and most videos are solved in 1.

$1.00 = 10,000 credits. The per-response rate is the contractual figure and is what your account is actually charged; the response counts above are what we typically see, not a guarantee — a captcha that fights back takes more, and you are billed for what was actually served.

Credits

Buy what you need. It does not expire.

Those counts are division, not an estimate — 3 credits per image response into the pack. Credits carry over indefinitely and are not tied to a billing period. Need volume pricing? Talk to us.

How billing works

Four rules, and no others.

Two things move your effective cost, and you should hear them here rather than infer them from an invoice. A reCAPTCHA grid re-draws after each click, so a session on a flagged IP draws harder challenges and lands above the typical response count. And if a vendor rejects a submission the model got right — a function of IP reputation and browser fingerprint more than of the answer — that response was still served and still billed. Tell us your setup and we will estimate it with you before you spend anything.

Common questions

Before you ask.