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

Annotations already provide readOnlyHint and idempotentHint, so the safety profile is clear. The description adds useful behavioral context beyond annotations: it ranks on the latest available quarter unless one is given, supports optional state restriction, and notes that no API key is required. It doesn't mention rate limits or pagination, but those are not critical gaps given the annotation coverage.

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 description is compact and front-loaded: the core purpose appears in the first sentence, followed by concrete examples and a minimal auth note. Every sentence earns its place, and the example calls are informative without being verbose.

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?

For a relatively simple ranking tool with fully documented optional parameters and safety annotations, the description covers inputs, defaults, state scoping, quarter selection, and example syntax. There is no output schema, but the description's focus on ranking makes the return shape intuitive enough for correct invocation.

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%, so the schema already documents all four parameters. The description adds value by connecting natural-language intent to parameter values (e.g., 'largest by assets' implies metric: 'total_assets') and by showing exact example calls with parameter syntax, which helps an agent construct valid invocations.

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 uses a specific verb and resource: 'Rank US credit unions by a call report figure,' with concrete examples like largest assets, most members, and biggest loan book. It also distinguishes this tool from sibling names like ncua_search_credit_unions, ncua_compare_credit_unions, and ncua_credit_union_profile by centering on ranking rather than search, comparison, or profile lookup.

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 provides clear usage context by answering natural-language questions ('largest credit unions in the US,' 'biggest credit union in Ohio') and explains optional state filtering and quarter selection. It doesn't explicitly name sibling alternatives or state when NOT to use this tool, but the purpose and examples make the appropriate invocation reasonably clear.

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