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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantially more: 0.1-2 s latency, USD 0.02 price, a 10-query/IP/UTC-day free tier, and a prompt-injection warning treating endpoint names/urls/on-chain strings as untrusted data. Cost, rate limits and injection risk are precisely the operational facts 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?

Purpose is front-loaded, followed by sibling routing, operational facts, and a safety note; every sentence carries decision-relevant information. It is dense and packs several facts per sentence, but there is no filler and nothing clearly droppable.

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 an output schema present, return values need no explanation, and annotations cover the safety profile. Description completes the picture with cost, latency, quota, routing to alternatives, and a data-trust warning, leaving nothing an agent needs before calling it.

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 all eight filters (q substring, page/page_size, source/network/category exact match, price bounds) are already documented in the schema. The description adds no parameter-level semantics beyond that, 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?

States a specific verb and resource: 'query a daily cross-registry index of x402 endpoints and MCP servers'. It immediately distinguishes itself from the sibling export/index tools by naming them and their distinct scopes, so 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?

Explicitly routes alternatives: 'For one file of up to 5,000 rows use export_agent_index; for one record's history use get_endpoint_history.' This gives when-to-use-this vs when-to-use-that with the selecting condition spelled out, which is exactly the routing guidance an agent needs.

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