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

With zero annotations, the description carries the full disclosure burden and does meaningful work: it discloses that calls are metered ($0.005 USDC on Base via x402/MPP) and that unpaid calls receive a 402 challenge, which is exactly the kind of auth/payment behavior an agent needs before invoking. It omits result limits, pagination, and match semantics (substring vs exact), which keeps it short of 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?

Three short sentences, front-loaded with the action and input, then the return shape, then the payment model. No filler; the only inefficiency is the misleading '(param: q)' parenthetical.

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-parameter search tool with no output schema, the description covers purpose, return fields and payment behavior adequately. The unresolved gap is the parameter identity/format, which is the one thing an agent must get right to call it successfully.

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?

The description names the input as 'param: q', but the schema defines a single required property named 'url' whose description is merely 'required'. This is a direct naming conflict that would lead an agent to pass the wrong key; the nominal 100% schema coverage is an artifact of a placeholder description and adds no real meaning. The description also doesn't clarify whether matching is substring or exact despite claiming search 'by URL or description'.

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+resource: searching the x402 endpoint census, with the returned fields (price, network, payee, first-seen) named explicitly. It is distinguishable from siblings like census_new, census_stats and census_price-changes, though those distinctions are left implicit rather than stated.

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?

No when-to-use or when-not-to-use guidance is given, and the sibling tools most likely to be confused with it (census_new, census_stats, census_price-changes) are never mentioned. The agent must infer that this is the lookup tool and the others are analytics/ingest tools.

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