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

Annotations already indicate read-only, idempotent, non-destructive behavior. The description adds useful behavioral context beyond that: it is 'Keyless', name matching is 'fuzzy', data comes from the NCUA call report, and the tool returns counts rather than detailed branch locations. This modestly exceeds the annotation baseline.

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 front-loaded with the core purpose and return fields, followed by useful example questions and invocation examples. It is a little longer than strictly necessary, but every sentence contributes practical guidance for selecting and calling the tool.

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 tool with three optional parameters and no output schema, the description covers purpose, key return fields, lookup methods, and an example. It does not explicitly direct agents away from sibling NCUA tools, but the 'full profile' framing and branch/ATM count distinction keep it sufficiently complete.

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 schema already documents all three parameters. The description reinforces the name vs. cu_number lookup choice with examples, but it does not add much new semantic detail beyond what the schema already provides, and the quarter parameter is only explained in 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 uses a specific verb and resource: 'Get a full profile for one US credit union from its NCUA call report.' It enumerates the returned data (assets, members, loans, deposits, etc.) and provides concrete example questions, making its purpose unmistakable. It also distinguishes itself from sibling tools by emphasizing 'full profile' vs. financials, rankings, or branches.

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?

The description clearly says to look up a credit union by charter number or name and provides two concrete invocation examples. It implies the tool is for one-entity profile questions, but it does not explicitly name alternative sibling tools or state when those alternatives should be preferred.

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