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

Annotations already mark this read-only, idempotent, and non-destructive; the description adds useful context beyond annotations by noting it is 'Keyless' and that figures are from NCUA call reports. It does not describe return shape or error behavior, but those are secondary for a safe read tool.

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?

Four short sentences, each with a distinct job: scope/metrics, example phrasings, input styles, and auth status. No filler or repetition; the most important information is front-loaded.

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 read-only comparison tool, the description covers what data is compared, how to pass inputs, an example, and keyless access. Missing an explicit statement about whether chartered numbers and names can be mixed, though the sibling set and schema make the tool otherwise easy to call.

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%, with the schema already documenting names as 2-5 credit union names and cu_numbers as charter numbers. The description reinforces the names-or-numbers choice and adds an example, but adds little parameter meaning beyond the schema.

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 specific action and resource: 'Compare two or more US credit unions side by side on their NCUA call report figures,' and names concrete metrics. This clearly distinguishes it from single-entity NCUA siblings such as ncua_credit_union_financials or ncua_rank_credit_unions.

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 gives explicit input mechanics ('Pass names or charter numbers'), a concrete example call, and natural-language query patterns. It does not explicitly name alternatives or state when not to use it, but the compare-two-or-more scope makes the fit clear.

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