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

No annotations are provided, so the description carries the full burden. It does disclose one useful trait — results are approximate great-circle values, not driving distance — but says nothing about invalid/unknown postal code handling, precision bounds, or rate limits. The auth requirement is only obliquely signaled by 'PRO'.

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?

Very tight, front-loaded, zero filler. The leading 'PRO.' fragment is unexplained jargon that costs a little clarity, but the core statement arrives immediately.

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 3-parameter tool with an auth token, no annotations, and no output schema, the description leaves too much unsaid: input format for postal codes, what happens on invalid input, and what the response contains beyond a km value.

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 only 33%, and the description only implies that 'from'/'to' are postal areas without specifying accepted formats (FSA-only vs. full postal code, spacing, casing). The access_token parameter is documented in the schema but never addressed in the description.

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?

Names a specific operation (great-circle distance) and resource (Canadian postal areas), and adds the unit (km) plus the 'approximate' qualifier. It does not distinguish itself from siblings batch_postal or postal_lookup, so an agent must infer which tool to reach for.

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?

'PRO' hints at a subscription tier but is never explained as a precondition, and there is no statement of when to use this versus batch_postal (bulk distances?) or postal_lookup (geocoding?). No alternatives or exclusions are given.

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