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

No annotations exist, so the description carries the full burden; it partially discharges that by enumerating the specific fields returned and flagging the PRO tier. It does not state that the operation is read-only, whether multiple years come back as a list, how many years of history are covered, or what the behavior is for non-990 filers or invalid tokens.

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?

One front-loaded sentence that leads with tier and scope, then enumerates the returned data – zero padding. The leading "PRO." is terse and slightly cryptic without context, but it is placed first where it matters most.

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 no annotations and no output schema, the field enumeration does real work to describe the return payload. Still missing for a 2-param tool is the response shape (single object vs. multi-year series) and access-failure behavior, leaving gaps an agent would want closed before calling.

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 50%: access_token is documented in-schema, while ein has no schema description. The description compensates for ein by saying the data is "for an EIN," clarifying it is the organization identifier, though it adds no format/lookup details (e.g., whether dashes are accepted).

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+resource: Form 990 financial history for an EIN, and enumerates the exact data domains returned (revenue, expenses, assets, liabilities, officer comp, program/overhead ratio). It is clearly a financial-detail tool rather than a status check or prospect list, so an agent can route it away from nonprofit_check/prospect_list, but the description never names those siblings to make the contrast explicit.

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?

"PRO." signals that a paid/subscriber credential is required, and the access_token param reinforces this, giving an implied precondition. However, there is no explicit guidance on when to choose this over nonprofit_check or prospect_list, and no statement about what happens for organizations that don't file a 990.

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