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

Goes well beyond the annotations: it confirms the URL path lists tools read-only, discloses a concrete cost (US$0.01 USDC on Base via x402) with the payment rail, and states the failure-billing rule ('servers that cannot be listed are not charged'). It also explains that pinned fingerprints are for detecting changed tools (rug pulls), which is behavioral context the readOnlyHint/openWorldHint annotations do not convey.

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

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

Three tight sentences, front-loaded with the purpose and threat model before the input modes and pricing. Every clause (including the pricing and no-charge rule) carries decision-relevant information; nothing is padding.

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

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

Covers input modes, cost, failure billing and the detection scope for a 4-parameter tool with no required fields. It never says what the audit result contains (verdict shape, per-finding detail), which matters somewhat since there is no output schema to fall back on.

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

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

Schema coverage is 100%, so the baseline is 3, but the description adds real meaning: it establishes the either/or relationship between url and tools (mutually exclusive input modes, which the flat schema does not express) and explains what 'pinned' is for. It does not clarify how 'instructions' interacts with the pasted-tools path.

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

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

States a specific verb and resource ('Check an MCP server for tool poisoning') and enumerates the concrete classes of problems it detects: hidden instructions, secrecy, sensitive-file access, cross-tool shadowing and rug pulls. The resource (an MCP server) is inherently distinct from siblings audit_skill, read_url and scan_content, so an agent can route correctly without opening the schema.

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

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

'before you connect' gives explicit timing context, and 'Pass its URL ... or paste its tools' tells the agent which input modes are valid. It stops short of naming when to prefer audit_skill or scan_content instead, so no exclusion guidance is present.

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