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

Goes well beyond the annotations: no auth/API key needed, shared client=vc-mcp quota of 5 free lookups per UTC day with a 00:00 UTC reset, the exact failure mode afterwards (HTTP 402, $0.02 USDC on Base via x402) and the crucial guarantee that it never pays and that payment never changes results. It also discloses result ordering, staleness signaling, and the facts_only exception — rich context an agent cannot get from readOnlyHint/openWorldHint alone.

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-loads the ranked-question framing and the sibling routing in the first two sentences, then packs quota, output shape and edge cases densely with no filler. It is long and information-dense rather than tight prose, which costs it a point, but nearly every clause carries a fact.

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 fully carries the return-value burden: sort order (pass_rate over last n paid calls, then price), the field list (price_usd, pass_rate, last_check_at, last_check, stale, receipts with tx/basescan_url/charged_usd/delivered/quality), the facts_only case for seller-broken services, and the empty-results behavior (matched 0). Nothing an agent needs to call or interpret this tool 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 description coverage is 100%, so params like n, limit and max_price_usd are already fully documented with ranges and clamps, making 3 the baseline. The description does add one genuinely useful constraint the schema lacks (required fields list is empty): 'Needs task or endpoint; invalid params return an error.' Beyond that it adds little parameter detail the schema doesn't already carry.

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 (rank) and resource (x402 endpoints) plus the exact question it answers, and explicitly distinguishes itself from search_catalog (keyword browsing, unranked) and get_service (one id's raw record). An agent can select it 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?

Gives the selection condition (known task at or under a price) and names both alternatives with the reason each is worse, plus a 'prefer it over' directive. When-to-use and when-to-use-something-else are both explicit.

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