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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so safety is covered. The description adds genuine provenance context — the list is XipFax's, sourced from the IRS's own pages — which is useful for trust, but it says nothing about what happens when no office matches or how results are shaped.

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?

Three short sentences, front-loaded with the core action and followed by input guidance in the order the parameters are used. No filler, though the imperative phrasing ('Give the form…') is slightly indirect compared to simply stating the input format.

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 no explanation, and both parameters are fully documented in the schema plus the description's conditional rule. The only gap is the no-match case, which an agent calling this tool would benefit from knowing.

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 a 3 is the baseline. The description goes beyond it by clarifying that the form should be given by name or number alone, and by stating the conditional rule that place is only needed where the IRS publishes per-state numbers — a relationship between the two parameters the schema does not encode.

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 names a specific verb and resource — finding the fax number of the IRS office that handles a given form or notice — and scopes the data source ('XipFax's list of offices, read from the IRS's own pages'). It does not explicitly contrast with the siblings quote_fax and send_fax_link, but the purpose is distinct enough that confusion is unlikely.

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?

Usage context is implied ('give the form or the notice by its name or number alone'), and the conditional rule for the place parameter is stated ('Where the IRS gives a number for each state, give the place too'). There is no explicit when-not-to-use guidance and no named alternative for related tasks such as quoting or sending a fax.

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