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

Adds a lot beyond the annotations, which only cover the read-only/idempotent safety profile: it discloses the extra values returned (section 382 rate, low-income housing credit percentages), the edge-case response for unissued months, and the returned ruling number and data_as_of. This is genuinely useful behavioral context for calling the tool correctly.

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-loads the core purpose and keeps the useful edge-case and return-value notes. The parenthetical explanation of the rate is somewhat long but earns its place by clarifying an obscure financial term.

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 a rich output schema and comprehensive annotations already present, the description adds exactly what is missing: extra return fields, the not-yet-published edge case, and source provenance. Nothing an agent needs to invoke it correctly is absent.

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 the schema already documents the 'YYYY-MM' / 'November 2026' formats and the newest-published default. The description's 'Omit month for the newest published' largely restates the schema default, so it adds little parameter detail beyond structured data.

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 (IRS Section 7520 rate for a month) and explains its use in estate/gift planning, which makes the purpose concrete. However, it does not distinguish itself from the sibling irs_afr tool, and both draw from the same Applicable Federal Rates ruling, so an agent still has to infer which one to call.

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 clear operating guidance: 'Omit month for the newest published' and notes that an unissued month returns 'not_yet_published' with expected timing. It stops short of naming when to prefer this over irs_afr, so there is no explicit alternative routing.

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