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

Adds substantial behavior beyond the readOnly/idempotent annotations: the upstream source (ProPublica Nonprofit Explorer), the result cap of 25, the exact fields returned, and the explicit absence of financials. The main omission is what happens when more than 25 matches exist — no guidance on pagination or refining the query, which matters for a capped search.

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, front-loaded with the trigger condition, then results, then the routing alternative, then the exclusion. No filler and nothing repeated from the name or title.

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?

An output schema exists so return shape needn't be spelled out, yet the description still summarizes returned fields and their source, which is useful for judging relevance. For a simple three-parameter read-only search, an agent has everything needed to select and call it correctly.

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?

With 100% schema coverage the baseline is 3, and the description does add a little: "optionally in one US state or one category" clarifies that state and category are single-value narrowing filters rather than multi-selects, and that name is the primary search key. It stops short of explaining matching behavior (prefix vs substring vs fuzzy), which the schema leaves ambiguous with "Part of the organization's name".

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 and resource ("find a US nonprofit or charity and its EIN by name") plus the optional narrowing dimensions (state, category). An agent can immediately distinguish this from get_nonprofit_profile because the description says the profile tool needs an EIN.

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?

Opens with an explicit trigger ("Use this when the user wants to..."), names the alternative for a related need (financials via get_nonprofit_profile), and gives an explicit exclusion ("Do not use for organizations outside the US"). It doesn't mention compare_nonprofits, but the when/when-not/alternative triad is otherwise complete.

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