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 goes well beyond them: it enumerates the returned plan fields (id, name, price per 1000, min/max quantity, quality tier, typed axes, delivery speed, recommended flag) and discloses an operational condition, that the endpoint only lists while the accountless x402 payment channel is on. That is real behavioral context not present in 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?

The purpose and routing alternatives are front-loaded, which is exactly right for selection. It runs long in the middle, with a dense parenthetical inventory of every returned field, but that detail is justified because there is no output schema; minor trimming is possible.

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 no output schema and a single parameter, the description carries the burden of explaining return values and does so completely, including the plan-level fields and the downstream service_option_id handoff. The only soft spot is the trailing x402 aside, which is slightly cryptic but does not block correct invocation.

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?

One parameter with 100% schema description coverage that already states the id comes from search_catalog, so the schema carries the load and the baseline is 3. The description reinforces provenance but adds no syntax or format detail beyond the schema; the service_option_id mentioned is an output, not this tool's input.

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+resource ('Look up ONE service you already have the id for') and immediately scopes it against siblings, explicitly noting that search_catalog finds ids and recommend_service picks a single option. An agent can distinguish it from all six siblings 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?

It states the precondition ('you already have the id'), the fallback for when that precondition fails ('No id yet? Find one with search_catalog'), and the alternative for the selection use case ('Use recommend_service'), plus the downstream handoff to get_quote and create_paid_order. When-to-use and when-to-use-something-else are both explicit.

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