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crosscheck

by com.crosscheckapi
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Security review of a skill or MCP server

skillcheck

Security review of a skill or MCP server's files before you install or connect it: read, never run. Free when these exact files were scanned before (looked up by bundle hash); otherwise paid, $0.03 base. Never says safe. Paid per call in USDC over x402 (Base, or free test USDC on Base Sepolia). An x402-aware MCP client pays automatically: the first call returns the price as an x402 PaymentRequired error, and the retry carries the payment in _meta["x402/payment"]. Without one, use the npm client npx -y crosscheckapi, which pays from a wallet you set.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
refNoOptional: the hash of a crosscheck receipt that brought you here. Its wallet earns check credits from your first 90 days of spend.
filesYesEvery text file of the skill or server, docs included; code rules read all of them
freshNoScan again even when a past scan of these exact files exists

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • addedInput schema / properties / ref
      Added value: +{
+  "description": "Optional: the hash of a crosscheck receipt that brought you here. Its wallet earns check credits from your first 90 days of spend.",
+  "pattern": "^[0-9a-f]{64}$",
+  "type": "string"
+}
  2. Changed2 schema fields changed
    • changedInput schema / properties / files / description
      Previous value: -"The skill's or server's text files"New value: +"Every text file of the skill or server, docs included; code rules read all of them"
    • changedInput schema / properties / files / maxItems
      Previous value: -50New value: +200
  3. First observed

TDQS

A4.1/5.0
Behavior5/5

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

With no annotations provided, the description carries the full burden and does so excellently. It discloses that the tool reads and never runs, that it never claims safety, and it thoroughly explains the payment mechanism, including the x402 error flow and retry behavior. This is far beyond typical transparency and leaves no ambiguity about side effects or costs.

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 description is dense but every sentence earns its place: purpose, safety, pricing, payment flow, and client instructions. It front-loads the core purpose and safety, then details the payment mechanism without fluff. The structure is logical and efficient, making it easy for an agent to parse quickly.

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

Completeness4/5

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

Given the tool's complexity (payment, error handling, client requirements), the description covers nearly all necessary context: what it does, how to pay, what happens on first call, and how to retry. It does not explicitly describe the return value format, but it states 'Never says safe,' implying a judgment output. Since there is no output schema, a bit more detail on the return could improve completeness, but overall it is quite thorough.

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?

Schema description coverage is 100%, so the schema already documents all three parameters (files, ref, fresh) with descriptions. The tool description does not add extra meaning about these parameters beyond what the schema provides, such as format or constraints. It mentions 'read, never run' but that is not parameter-specific. Thus, a baseline 3 is appropriate.

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

Purpose4/5

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

The description clearly states the tool performs a security review of a skill or MCP server's files, with the key qualifier 'read, never run.' This is a specific verb-resource pair that distinguishes it from typical execution tools. However, it does not explicitly name sibling tools like accept, check, result, or skillcheck_lookup to differentiate them, so it falls short of a perfect 5.

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?

The description gives clear context: 'before you install or connect it' and explains when it is free vs. paid based on prior scans. It also details how to use it with an x402-aware client or the npm fallback. It does not explicitly mention alternatives or when not to use this tool, but the context is strong enough for an agent to decide.

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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