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

Annotations already note read-only and idempotent. The description adds critical behavioral nuances: the 'id' field is the API key's row ID (not the user ID), 'userName' can be null, and 'team' serves as project ID for project-scoped keys. It also clarifies how the output maps to other tools' expected entityId format, which is far beyond 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?

The description is a single dense paragraph but well-organized, front-loading the core purpose and then adding crucial clarifications. It could be broken into shorter sentences for readability, but every sentence adds value and avoids fluff.

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 zero-parameter tool with no output schema, this description is highly complete. It identifies common pitfalls ('id' vs 'user'), defines null behavior, and explains usage across token scopes. An agent has everything needed to use the tool correctly and interpret results.

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?

There are no parameters, so the schema requires no parameter documentation. The description focuses on return values instead, and per rubric, zero parameters receive a baseline of 4, which is appropriate here.

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?

Clearly states it returns information about the current API key and specifies the contents (user email/name, project/team). The verb 'Returns' and resource are specific, and the tool is distinct from siblings like 'ping', though it does not explicitly contrast itself with any sibling.

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?

Explicitly says it is 'Useful to verify authentication and retrieve your user ID or project ID,' giving clear context for when to call it. It does not mention alternative tools or exclusion criteria, but the use cases are well-defined.

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