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

Annotations only cover readOnly and openWorld. The description adds substantial context beyond them: the pay_to divergence warning surfaced at top level and endpoints[].pay_to_divergence, the meaning of include_series and its cost, and the crucial caveat that the price field is atomic token units rather than dollars. This is exactly the kind of behavior-shaping detail an agent cannot get from structured fields.

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 purpose and the when-to-call condition in the first clause before piling on the returned fields. It is dense and slightly run-on across the warnings and units sentences, but every sentence carries actionable information, so little is wasted.

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 carries the full burden and meets it: it describes the record's contents, optional series, the conditional warnings path, and the units convention. An agent knows what it will get and how to read it without guessing.

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. The description reinforces include_series by tying it to concrete value ('90 daily points of on-chain volume and distinct buyers'), which slightly overlaps the schema but clarifies intent. The units-map note is about interpreting output, not the slug/include_series params, so it doesn't lift this dimension further.

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 (fetch the full service record behind a directory row) and enumerates what it contains: live status, uptime windows, response time, networks/settlement asset, priced endpoints, assessment block. The framing 'once you hold a slug' cleanly separates it from search/find_best siblings that the agent uses before it has a slug.

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 an explicit trigger: call once you hold a slug and are deciding whether to commit. This implicitly routes the agent away from x402_search_services / x402_find_best_service, which are the pre-slug tools. No explicit when-not or named alternative, so it falls short of a 5.

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