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

Annotations already establish readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable context beyond those: the data source and corpus size (~1.27M orgs), the specific fields returned, and the hint that this returns a less-decoded record than nonprofit_details. Nothing contradicts the 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?

Two sentences with zero waste: the first packs verb, resource, scope, data source, corpus size, and return fields; the second routes to the decoded alternative. Information is front-loaded and every phrase 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?

For a simple one-parameter lookup with rich annotations and no output schema, the description covers the data source, the matching scope, returned fields, and the relationship to nonprofit_details. A minor gap is not stating behavior when the EIN is not found or when to prefer nonprofit_status, but these are small against an otherwise complete definition.

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% — the ein parameter already documents the 9-digit format with or without dash and gives examples. The description's 'exact EIN' adds a mild semantic of exact-match behavior, but the schema carries the format burden. Baseline 3 is appropriate.

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?

States a specific verb ('Look up'), a precise resource (US tax-exempt org by exact EIN from the IRS EOBMF), and names the return fields (name, address, IRC subsection, EO status). The 'exact EIN' qualifier distinguishes it from the nonprofit_search_name and nonprofit_search_location siblings without needing to inspect their schemas.

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 'exact EIN' phrasing implies this tool is for precision lookups rather than fuzzy search, and the explicit pointer 'Use nonprofit_details for the fully decoded record' names a concrete alternative. However, it does not explicitly tell an agent to use nonprofit_search_name or nonprofit_search_location when only a name/location is known, leaving some routing to inference.

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