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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely non-redundant behavior: the call costs nothing, performs no network I/O, and the prices it reports are per-call USDC amounts on Base via x402 — that clarifies what the price field means.

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?

A single dense sentence with no filler; the resource and count come first, followed by returned fields, then cost and network behavior as trailing qualifiers. Every clause carries information.

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?

No output schema exists, so the description must carry the return shape, and it does — listing exactly which fields each endpoint entry contains. The cost model is also spelled out. Only the pagination/ordering question is unaddressed, which is minor since the full set is a fixed 78 entries.

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 both `search` (substring match on path/description) and `category` (enumerated) are fully documented in the schema. The description says only that 'accepted parameters' are among the returned fields and adds nothing about filtering, so the baseline 3 applies.

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?

Specific verb (List) plus a clearly bounded resource (Mercury402 financial data endpoints, 78 total), and it enumerates the fields returned (path, method, category, description, price, accepted parameters). It never names the sibling get_endpoint_data, so the differentiation is implicit rather than explicit.

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?

"Free; makes no network calls" hints that this is the discovery/browse step before calling an endpoint, but the description never states when to use this versus get_endpoint_data, or that the sibling is the paid fetch. The agent must infer the workflow.

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