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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's job is to add context — and it does: it discloses the calculation is optional, that results include scope notes, the source and an as-of date, and that the tax year is the latest published. It does not mention rate applicability dates or failure modes, but the added disclosure is meaningful.

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?

Front-loaded with what the rates are and who they apply to, then the optional calculation and return shape. Dense but no filler; slightly long in the trailing sentence enumerating return fields.

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?

A read-only, zero-required-parameter reference tool with full schema coverage, annotations and an output schema. The description supplies scope, applicability, province semantics and return-shape reassurance, leaving little an agent would need to guess.

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% and each parameter already carries a description (including the 'caps meals at the daily maximum' and 'needs province' constraints). The description mostly restates that meals and vehicle amounts are optional calculations, adding little beyond the schema, so baseline 3 is correct.

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 simplified-method meal and vehicle rates, latest published tax year) with concrete detail: flat meal rate per meal, daily maximum, cents/km by province. It explicitly contrasts with employer per-diems, though it does not name the closest sibling, cra_automobile_allowance_rate, which an agent could confuse with the vehicle-rate portion.

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 explicit applicability ('moving expenses, northern residents deductions and medical travel') and an explicit exclusion ('not to employer per-diems'), which is real when/when-not guidance. It stops short of naming an alternative tool for the excluded case, so the routing is incomplete but solid.

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