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

Annotations already declare readOnlyHint and openWorldHint, and the description adds useful behavioral details beyond that: the free price point, the hourly rate limit, and the exact return shape (pass/warn/fail, problem count, top three). No contradiction exists between the description and annotations.

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?

The description is compact and dense with value, leading with 'Free' and the core question. The sibling routing adds a bit of a list-like tail but remains within a single short paragraph; no wasted words.

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 lightweight read-only check tool with no output schema, the description covers return values, rate limits, cost, and routing to siblings. It does not describe what specific problems are reported, but that is a minor gap for a quick-check tool.

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 description coverage is 100%, so the schema already documents url and method. The description adds no new parameter-level meaning beyond naming the endpoint context; it relies on the schema, which is acceptable given the high coverage.

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?

The description opens with a precise, answerable question: 'does this x402 endpoint work for a paying agent?' and names its output (pass, warn or fail with problem count and top three). It clearly differentiates itself from sibling tools by naming x402_diagnose, x402_fix, and x402_preflight with their distinct purposes.

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 explicitly routes to alternatives: use x402_diagnose for every check, x402_fix for code changes, and x402_preflight before paying someone else's endpoint. It also states the free tier and 10-calls-per-hour limit, which informs when the tool may or may not be appropriate.

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