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

The description discloses behavior beyond the annotations: the hosted endpoint is discovery-only, returns HTTP 402 with price and x402 payment instructions instead of data, and requires either a separate x402 client or running mercury402-mcp locally with a wallet. This is consistent with openWorldHint=true and readOnlyHint=false.

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 front-loaded with the key limitation and usage path, then moves into practical calling details. The sentences are dense and purposeful, with no filler.

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 an open-world, non-idempotent endpoint-calling tool with no output schema, the description covers enough for correct invocation: discovery-only behavior, payment flow, local alternative, sibling-tool sequencing, and parameter placement. Nothing critical for an agent 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%, so the baseline is 3, but the description adds meaningful composition semantics: path parameters may be inline or supplied in params, and other parameters are routed to query string or JSON body depending on the HTTP method. The pay parameter's behavior is mostly left to the schema.

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 states a specific action and resource: calling a Mercury402 endpoint on the live API. It immediately distinguishes the tool from list_endpoints by saying list_endpoints is used first to discover paths and parameters, and it clarifies that hosted discovery calls return HTTP 402 pricing/payment instructions rather than data.

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?

It gives explicit routing guidance: use list_endpoints first to find paths and parameters. It also explains how to supply parameters, including inline path params versus params-object path params, and how remaining params are sent as query strings for GET or JSON bodies for POST.

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