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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description adds the useful extras: the null-result case when no price exists, the meaning of is_estimated, and the partner-key auth requirement. It does not describe rate limits or the shape of StationPrice, which matters since there is no output schema.

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 sentences, front-loaded with the resource and scope, then return shape, then the estimation caveat and auth note. Dense and mostly waste-free, though the auth sentence could be compressed.

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, the description correctly fills in the return envelope ({ data: StationPrice } or { data: null }) and the estimation semantics, plus the auth requirement. The internal fields of StationPrice remain undefined, which is the main residual gap for a 3-parameter lookup tool.

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 baseline is 3, but the description earns a bump by explaining that an is_estimated price is 'modeled from nearby observations' and by restating the pf_+16-hex id contract tied to diesel_prices_near. It adds interpretive meaning rather than merely repeating field descriptions.

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 — posted retail diesel price for one truck stop — and scopes it to a single station identified by public id. The singular 'one truck stop' plus the id format implicitly separates it from the plural sibling diesel_prices_near.

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 routes the agent by naming diesel_prices_near as the source of station ids, implying a discovery-then-lookup chain. It also states the precondition 'Partner keys only; send partner_tenant_ref with every call.' It stops short of explicitly saying when to prefer this over fuel_market_snapshot or optimize_fuel_plan.

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