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

Goes well beyond the readOnlyHint/openWorldHint annotations by disclosing the payment model ($0.10 USDC per call, failed calls free, omit `payment` for a quote), the data provenance (Coinbase's Bazaar catalog), and the refresh cadence (rebuilt weekly). These are operational facts an agent cannot infer from annotations or schema.

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 and cleanly labeled with 'When to use / Use instead / Returns', which makes it scannable. However, the seller-field list and the 'rebuilt weekly' fact are each stated twice almost verbatim (opening sentence vs. Returns line), which is avoidable repetition in a short description.

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?

With no output schema, the description carries the return-shape burden and does so fully, listing every field plus category totals. One optional parameter, zero required, pricing and cadence disclosed — nothing an agent needs to call it correctly is missing.

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% and the schema already documents the quote-vs-pay flow for `payment`, so the baseline is 3. The description reinforces the flow with the cost consequence ('Failed calls cost nothing'), which adds meaning about the economics of the parameter rather than just restating its syntax.

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 ('Get the whole x402 market as one dataset') and enumerates exactly what the dataset contains (rank, 30-day calls, revenue, paying wallets, categories, labels, category totals). It explicitly distinguishes itself from x402_seller_lookup and best_x402_tools, so an agent can route without opening any 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?

Has an explicit 'When to use' condition ('analysing the whole x402 market and want every seller in one file') and a 'Use instead' clause naming the two cheaper alternatives for single-seller or task-scoped queries. This is the full when/when-not/alternative triad.

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