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

Annotations already establish the safe read-only, idempotent, closed-world profile, so the description only needs to add context beyond that. It does add useful traits: the rates are for the latest published tax year, and amounts are computed only optionally, which clarifies that a bare call is a valid lookup.

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?

Two sentences that lead with the resource and rate shape before scoping and the optional calculation. Dense but each clause carries information; only 'Optionally calculates amounts' is slightly vague about what triggers calculation.

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?

An output schema exists, so return values need not be explained. Combined with the applicability scope, tax-year currency note, and the optional-parameter behavior, an agent has everything needed to invoke it correctly.

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 100%, so each of the four parameters is already documented, including the dependency that kilometres needs province and that days caps meals at the daily maximum. The description adds little beyond this, so the baseline of 3 applies.

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 resource (CRA simplified-method meal and vehicle rates) and states the shape of the returned data (flat meal rate per meal, daily maximum, cents/km by province/territory). It does not explicitly differentiate from the sibling cra_automobile_allowance_rate, whose subject matter overlaps with the vehicle portion, leaving a potential ambiguity.

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?

Gives concrete applicability scope — moving expenses, northern residents deductions, medical travel — plus an explicit exclusion (not employer per-diems), which is real when-to-use guidance. It stops short of naming the sibling tools or stating when a different rate tool should be chosen instead.

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