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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds a lot beyond them: typical latency (0.1-2 s), USD 0.02 price, 10 free queries per IP per UTC day, a has_more pagination signal, and an explicit warning to treat endpoint names/urls/on-chain strings as untrusted data. That trust and cost disclosure is exactly the extra context annotations cannot carry.

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?

Every sentence earns its place and is front-loaded: purpose, then inputs, then returned record fields, then latency/cost/quota, ending with the data-trust caveat. It is dense but not padded.

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?

Even without an output schema, the description names the returned fields (source, id, name, url, category, price_usd, network, first_seen, last_seen) and the has_more flag. For an 8-param all-optional read tool, nothing needed to invoke 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 description coverage is 100%, so the schema already documents each parameter. The description restates the filter set but adds no syntax or format detail beyond what the schema provides, making the baseline 3 appropriate.

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 gives a specific verb and resource: 'query a daily cross-registry index of x402 endpoints and MCP servers.' This is clearly distinguishable from siblings like bulk_agent_index, export_agent_index, or scan_agent_package, so an agent can select it without opening another 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?

It enumerates every filter (source, category, network, price range, q, paging), which implies how to narrow results, and it discloses the free-tier limit of 10 queries/IP/day. However, it never states when to prefer this tool over bulk_agent_index or export_agent_index, so routing guidance is only implied.

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