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

Annotations already declare readOnly/idempotent/openWorld/destructive=false, and the description adds substantive behavior beyond them: Medicare pays by LOCALITY not state, so a state or ambiguous name returns every matching locality rather than one 'chosen quietly,' the resolution is stated, the year default is stated, and the work GPCI is the floored CMS-paid value. These are exactly the ambiguity/fallback behaviors an agent needs.

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 the core question and answer, then progressively adds routing and examples. It is on the long side — the quoted example-query list overlaps with the later input guidance — so a bit of trimming is possible, but almost every sentence earns its place.

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, yet the description still characterizes the return payload and default/resolution behavior. For a 4-param, all-optional lookup tool, this is complete enough to call 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 the baseline is 3, but the description adds example-driven semantics ('FL' or 'Florida', 'Bakersfield', '99') and notes locality_number's dependency on state/locality for disambiguation. This goes modestly beyond the schema without adding new syntax the schema lacks.

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?

Opens with a specific question the tool answers ('Medicare geographic adjustment indices (GPCIs) for a place') and names the exact returned values (work, practice-expense, malpractice). It also distinguishes itself from siblings medicare_fqhc_gaf and medicare_physician_payment, so an agent can route without opening any schema.

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 invocation guidance (pass state/locality/locality_number; year defaults to newest loaded) plus named alternatives for adjacent needs ('For the FQHC-specific adjustment see medicare_fqhc_gaf; for a dollar payment see medicare_physician_payment'). Example queries further pin the intended usage.

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