capskip-mcp

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Solve ALTCHA

capskip_solve_altcha

Solve ALTCHA proof-of-work challenges by fetching the challenge URL or providing challenge JSON, and get a verification token for the altcha form field.

Instructions

Solve an ALTCHA proof-of-work challenge. ALTCHA is not a recognition captcha — there is nothing to read; the client brute-forces a number that satisfies a challenge, so a solve is deterministic and takes milliseconds. Give it either challenge_url (the endpoint the fetches from, which CapSkip will fetch) or challenge_json (the challenge document itself). Returns a token to put in the page's form field named altcha, verbatim. IMPORTANT: challenges expire quickly — some sites inside two minutes — so read the challenge immediately before calling and submit the token promptly. An expired challenge is rejected with a bare "verification failed" that looks exactly like a wrong answer.

Input Schema

TableJSON Schema

Name	Required	Description
`url`	Yes	Full URL of the page the captcha appears on, including scheme.
`proxy`	No	Fetch the challenge through this proxy. Used ONLY for the challenge_url fetch — an inline challenge_json never touches the network.
`timeout`	No	Seconds to wait before giving up. Maximum 600.
`challenge_url`	No	The endpoint the ALTCHA widget fetches its challenge from, e.g. 'https://site.com/altcha/challenge'. CapSkip fetches it for you. Pass this or challenge_json.
`challenge_json`	No	The challenge document itself, as a JSON string, when you already have it. Solved locally with no network request. Pass this or challenge_url.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`code`	Yes
`token`	Yes
`number`	No
`captchaId`	Yes
`solveSeconds`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Addedv1.1.0Sep 17, 2026

TDQS

A4.5/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description adds substantial behavior beyond the annotations: challenges expire quickly, an expired challenge produces a bare 'verification failed' indistinguishable from a wrong answer, and challenge_url causes CapSkip to fetch the endpoint while challenge_json is solved locally. It also characterizes the solve as deterministic and fast, which is exactly the operational context an agent needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The definition is front-loaded with the core purpose, then states the two input modes, the return-value placement, and a targeted expiration warning. Every sentence earns its place; the important operational warning is placed clearly and does not bloat the text.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Combined with a 100%-covered input schema and an output schema, the description covers the full workflow: what to read, which inputs to supply, what to do with the token, and the critical failure mode. Nothing needed to invoke the tool correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema already documents all five parameters with descriptions, and the description mostly restates the challenge_url/challenge_json choice that the schema already explains. It adds workflow-level color (fetch versus local solve) but no new constraints or formats beyond the schema, so the schema-coverage baseline of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with 'Solve an ALTCHA proof-of-work challenge', naming a specific verb, resource, and task. It differentiates the tool from recognition-based captcha solvers by explicitly stating there is nothing to read and that the solve is deterministic, so an agent can distinguish it from sibling captcha tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives clear when-to-use context: for an ALTCHA challenge, pass either challenge_url or challenge_json, with the trade-off that challenge_json is solved locally with no network request. It does not explicitly name sibling tools or state when not to use this tool, but the proof-of-work vs recognition contrast plus the two alternative inputs make the intended use clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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