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

No annotations are provided, so the description carries the full burden. It discloses that this is a read-only identity check (returns, no side effects implied), the exact fields returned, and that scope failures in other tools motivate calling it. It does not mention idempotency or rate limits, but those are minor for a zero-parameter identity probe.

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 tightly written sentences: the first front-loads purpose and return fields, the second gives usage guidance and rationale. No wasted words.

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 identity tool with no output schema and no annotations, the description fully compensates by listing return fields and explaining the call-first prerequisite. An agent has everything needed to invoke 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?

The tool has zero parameters, so the baseline of 4 applies. The description appropriately adds no parameter semantics since none exist.

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 'Returns' and the resource 'identity of the authenticated API key', and enumerates the exact fields returned (user_id, scopes, site_ids). This clearly distinguishes it from sibling tools that operate on runs or sites.

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 'Call it first when you do not know which sites the key reaches or which scopes it holds', giving both the condition and the reason ('every other tool fails on a missing scope'). This directly informs when to choose this tool over any sibling.

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