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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds real context beyond them: the data source (provider's published OpenAPI, read daily) and, unusually, the commercial terms ($0.005 USDC per call via x402 on Base or Solana, signed). It stops short of return-format or identity details, so not a 5.

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?

Front-loaded with what the record contains, then source, then fallback behavior, then pricing. Every clause is load-bearing. The payment/signing sentence is a little dense and could be cleaner, but nothing is wasted.

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?

For a single-argument, no-output-schema tool, the description covers the return fields, data provenance, freshness, and the payment requirement, which is what an agent needs to invoke it. It leaves the format of name and the meaning of 'Signed'/who the publisher is slightly ambiguous.

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?

With only one optional parameter and 0% schema description coverage, the description carries the burden and does so: it explains the dual behavior of name= (record for one API vs. listing all watched APIs when omitted). It does not explain the expected value format for name, so it misses full marks.

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 resource (one public API's contract record) and enumerates exactly what the record contains: version, operation count/keys, deprecated operations, security schemes, and 90-day dated changes. It even covers the no-argument fallback (lists watched APIs). It does not explicitly contrast itself with the closest sibling apis_changes, so it falls short of a 5.

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?

The description implies the call pattern ('Without name=, lists the APIs we watch') and surfaces the paid prerequisite, but never says when to choose this over apis_changes or any other sibling. Usage is inferable rather than stated, which is the definition of a 3.

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