CaptchaSonic's MCP server: captcha solving for AI agents

What the MCP route is

The Model Context Protocol is, in its own documentation's words, an open-source standard for connecting AI applications to external systems. Plug a captcha solver in through it and the solver becomes a tool the agent can call. When a page throws a challenge, the agent hands it to the solver and gets the answer back, without anyone copying keys or tokens around.

Underneath, nothing changes. The solver still runs the loop every captcha API runs (a task created, a result polled, a token returned), and the token still expires on the captcha provider's clock. How a captcha solving API works covers that loop. This guide covers how CaptchaSonic exposes it to an agent.

Hosted or local

CaptchaSonic publishes its server on npm as @captchasonic/mcp-server, under the MIT licence. The package first appeared on 30 May 2026, and version 2.0.0 went up on 6 October 2026. It runs two ways.

Hosted, there's nothing to install: the client points at https://mcp.captchasonic.com and sends the API key as a bearer token. Local, the client starts the package with npx over stdio and passes the key in SONIC_API_KEY, which needs Node.js 20.3 or later. The hosted route needs no Node.js on your machine; the local one keeps the server process on it.

The commands below follow Claude Code's own syntax: claude mcp add --transport http with a --header for a bearer token, or --env and a -- separator for a local process. Claude Code adds a server to the current project by default. CaptchaSonic's docs give the same server as JSON configuration for Cursor, Windsurf and Antigravity.

1. 1
   Get an API key

   Sign up at my.captchasonic.com. Keys start with sonic_, and new accounts get starter credit without a card.

2. 2
   Add the hosted server

   claude mcp add --transport http captchasonic https://mcp.captchasonic.com --header "Authorization: Bearer sonic_xxx"

3. 3
   Or run it locally

   claude mcp add captchasonic --env SONIC_API_KEY=sonic_xxx -- npx -y @captchasonic/mcp-server

4. 4
   Check it

   Ask the agent to call get_balance. A wallet balance back means the key works.

The five tools

Once connected, version 2.0.0 gives the agent five tools. With list_captcha_types an agent can read a type's price before it spends anything.

The Claude Code plugin

For Claude Code there's also a plugin. Two commands add it: /plugin marketplace add captchasonic/captchasonic-skill, then /plugin install captchasonic. It brings three skills (captchasonic-setup, captchasonic-solve and captchasonic-balance) and ships a configuration that registers the MCP server on install. The API key still has to be set once.

A lighter plugin wraps the SDK instead of the server. sonic@captchasonic, from the captchasonic/sonic-sdk marketplace, adds /sonic:solve, /sonic:balance and /sonic:test-sdk.

What a solve costs from an agent

An agent pays the same per-solve prices as any other client, so the price list in CaptchaSonic's review applies unchanged. The rows an agent meets most:

What raises the bill in an agent loop

Retries first. Google's documentation states that a reCAPTCHA token is valid for two minutes and can be verified once, so every retry needs a new solve, and every solve is charged.

Then waiting. The two minutes run from the moment the token is generated. An agent that solves first and thinks afterwards can pay for tokens it never submits. The token budget has the arithmetic.

The other solvers with an MCP server

CaptchaSonic isn't alone here. Three other vendors reviewed on this site publish MCP servers under their own GitHub accounts.

How they differ

Scope is the big difference. 2Captcha's package is the broadest by far, a scraping toolkit with solving inside it. CaptchaSonic's is the narrowest and the most focused on solving. With 2Captcha's, it's one of the two you can use without running anything locally.

CapSolver and CapMonster Cloud ship Python servers you run yourself. CapSolver's can serve over HTTP once you host it; CapMonster Cloud's speaks stdio only and leaves hCaptcha out.

One gap is worth knowing. The official MCP Registry lists the CapSolver and CapMonster Cloud servers, and a search there for CaptchaSonic returned nothing on 11 October 2026. A client that discovers servers through the registry won't find CaptchaSonic's yet.

What the server can't do

It returns a valid token or answer. Whether the page then lets the agent through depends on the site's own checks and on the address the request comes from, which no solver changes. Why the exit address decides your captcha rate covers that half.

And the speeds are the vendor's. The price list states ceilings of 12 seconds for reCAPTCHA v2 and 13 for Turnstile, and its comparison table claims an average reCAPTCHA v2 solve under 3 seconds. We didn't run solves through the server to measure either.