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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely useful behavior it could not get elsewhere: the embedded schema version, the presence of max_age_seconds, and the access-tier difference where free callers see a masked publisher while a router key reveals the source name. That last point is real behavioral disclosure about results varying by credential.

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?

Four short clauses, front-loaded with the core action and identifier format, with no filler sentences. The 'Schema swapeazi.rate_receipt.v1.' fragment is terse to the point of being cryptic, but it is informative rather than wasteful.

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 a simple two-parameter read with no output schema, the definition covers the action, the id provenance, the access-tier variance, and even one returned field. What is missing is minor: nothing about errors for a missing or expired receipt, though max_age_seconds hints at expiry.

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, and the description earns an increment by explaining the effect of access_key: it changes whether the publisher is masked or the source name is visible. That gives the optional parameter meaning the schema description alone ('a router key, if not sent as a Bearer header') does not convey.

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 — 'Return a stored Rate Receipt by id' — and pins the identifier format (rr_...) plus the schema version (swapeazi.rate_receipt.v1). That is enough to separate it from siblings like price_routes or rate_deal_history, though it does not name those siblings explicitly.

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?

Usage is implied rather than stated: the id is described as coming 'from price_routes', so an agent can infer this is a follow-up lookup after pricing. But there is no explicit when-to-use versus when-to-use-an-alternative guidance, and no statement of what happens if the id is unknown or expired.

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