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

Annotations only declare the generic mutation profile (readOnly=false, idempotent=false, destructive=false); the description adds real behavioral context: automatic pricing at the approved rate, tiering after 10,000 car miles, and a Pro-plan gating requirement. It stops short of saying what the response contains or whether entries can be amended.

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 action and then progressively adding pricing, the eligibility exclusion, and the plan gate. Every sentence carries distinct information, though the pricing/tiering detail is useful context rather than action-critical.

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 6-parameter mutation with no output schema, the description covers the semantic rules an agent most needs: what counts as business mileage, how it is priced, and the plan restriction. Remaining gaps (return value, permissions beyond plan gating) are moderate.

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 low (33%), so the description carries more weight than usual. Its mention of 'car miles' and the tiering rule indirectly signals that the vehicle type affects pricing, but it adds nothing about from/to/date/purpose, leaving most parameters documented only by their bare schema types.

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+resource ('Record a business journey in the signed-in person's mileage log'), clearly distinct from the read-only sibling get_mileage_summary. An agent can identify this as the write-side mileage tool without opening the 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?

Provides a clear exclusion rule ('Commuting to a permanent workplace is not business mileage') and a prerequisite ('Mileage tracking is on the Pro plan'). It doesn't explicitly name get_mileage_summary as the read counterpart, so routing guidance is good but not exhaustive.

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