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

Beyond the annotations, the description adds meaningful behavioral context: 'No side effects. Idempotent. US only. 7-day cache. Verified source: IRS EO BMF + IRS TEOS.' It also discloses that it returns data from the most recent 990 filing. No contradictions with annotations.

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 dense but not bloated. It front-loads purpose, then covers parameters, return fields, usage guidance, source, cache, and feedback fallback. The feedback sentence is long but contains actionable specifics, so it 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?

With one well-documented parameter, an output schema, and annotations covering safety, the description is complete. It adds return fields, source, cache behavior, usage guidance, and a fallback feedback path. Nothing needed for correct invocation is missing.

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 baseline is 3. The description adds extra value by clarifying the EIN format: '9-digit Employer ID with or without dash, e.g. 46-5734087 or 465734087.' This goes beyond the schema's format example.

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 states a specific verb and resource: 'Fetch IRS 990 filing data for any US nonprofit by EIN.' It also names the sibling alternative (nonprofit_search_nonprofits_by_name) and clarifies this tool is for exact EIN lookups, making it easy to distinguish from related nonprofit tools.

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?

Explicit usage guidance is provided: 'Use this when you have the exact EIN. Use nonprofit_search_nonprofits_by_name instead when you only have a name.' This clearly states when to use the tool and when to use an alternative.

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