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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds genuinely behavioral detail: the tool honors the mid-year 2026 split (72.5 cents through June 30, 76 cents from July 1), returns auxiliary values (35-cent depreciation component, $61,700 FAVR maximum), and explicitly reports that 2027 rates are unavailable instead of failing.

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?

The most important information – purpose, units, categories, and the mid-year caveat – is front-loaded in the first two sentences. The remaining sentences pack in many specific figures (72.5, 76, 20.5, 23.5, 14, 35, 61,700); each is useful but the density approaches list-like rather than prose.

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?

There is no output schema, so the description carries the return-value burden and does so: units (cents per mile), categories, the depreciation component, and the FAVR maximum value. It also covers the edge case of unannounced future years, which is the main failure mode an agent would hit.

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 both parameters (date pattern YYYY-MM-DD, year 2011-2100, default 2026) are already documented. The description reinforces the date semantics by noting the mid-year switch, but adds little beyond what the schema fields state, so baseline 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?

The description opens with a precise verb and resource: 'Returns the official IRS standard mileage rates in cents per mile for business, medical, charity and military moving use.' That is enough for an agent to distinguish it from calculate_mileage_deduction, which computes a deduction rather than looking up statutory rates.

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?

It states the two lookup modes ('for a year or a specific date') and the boundary that 2027 is not yet announced, but it never explicitly tells the agent when to call this versus calculate_mileage_deduction. The when-to-use is inferable from the purpose, not spelled out.

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