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

Annotations already establish this as a safe, idempotent, closed-world read. The description adds real context beyond them: the 2026 default with 2025 also available, the two-tier kilometre structure (first 5,000 km and after), and the province-vs-territory rate split. It does not mention rate publication/update cadence or limits, keeping it short of a 5.

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?

A single dense sentence with the core resource and defaults front-loaded and the optional calculation tacked on last. No wasted clauses, though the parenthetical and tier list make it slightly heavy to parse.

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 an output schema present, return values need not be described, and the description covers the dimensions an agent needs: year options, rate tiers, and province/territory variation. The one gap is that it never states what happens when province is omitted, which matters for a tool with zero required parameters.

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. The description goes slightly beyond the schema by signaling that the year defaults to 2026 and that province/territory choice materially changes the rate tiers, which is a meaningful semantic hint about why the province parameter exists.

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 resource (CRA reasonable per-kilometre allowance rates) with clear scope: employer-paid vehicle allowances, 2025/2026, first 5,000 km vs after, provinces vs territories. This is distinguishable from siblings like cra_meal_travel_allowance or the GST/HST rate tools without opening any 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?

The phrase 'Optionally calculates the allowance for a number of business kilometres' implies when the kilometres parameter applies, but there is no explicit when-to-use guidance, no when-not-to-use, and no routing to alternative siblings. Usage is inferable rather than stated.

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