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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds two things the annotations cannot: the required authorization scope and a security warning that user-written text arrives in untrusted_fields and must be treated as display-only data, not instructions. That is substantive behavioral context, though it does not describe the shape or limits of the estimate itself.

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?

Three short sentences, front-loaded with the purpose before the permission and safety notes. The untrusted_fields sentence is somewhat generic boilerplate but earns its place as a prompt-injection guard for a tool that surfaces human-written text.

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?

The tool is simple (two required scalars, no nesting, no output schema), and the description covers purpose, auth, and unsafe-input handling. It still leaves an agent without any statement of what an estimate contains (duration, distance, mode) or what proposal_id refers to, which matters given the absence of an output schema.

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 description coverage is 0%, so the description carries the full burden for the two parameters. It never mentions proposal_id or origin; only the word 'travel' hints that origin is a starting point, and nothing clarifies whether origin is a free-text address, coordinates, or an ID. An agent must guess at both parameter meanings.

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 plus resource: 'Estimate the travel to a booking', which tells an agent exactly what the call computes. It does not distinguish itself from adjacent read tools such as get_booking_proposal or get_availability, so it falls short of a 5.

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?

The scope requirement 'Needs `bookings:read`' is a genuine prerequisite that helps an agent decide whether it can call at all. Beyond that, there is no explicit when-to-use or when-not-to-use guidance and no named alternative for related booking lookups, leaving usage to inference.

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