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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered structurally. The description adds real behavioral context beyond that: it is a diagnostic call whose purpose is to prevent futile retry loops on permission errors, and it hints at the shape of the response ('what each unlocks'). It stops short of describing return format explicitly, but with no output schema that is a minor gap.

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, zero waste: the first front-loads what the agent gets back, the second front-loads the trigger condition and the alternative to avoid. Every clause 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 zero-parameter, no-output-schema tool, the description carries the full burden of explaining returns and does so adequately ('granted scopes and what each unlocks'). The only shortfall is that it does not say whether the response enumerates specific tools or resources blocked by missing scopes, which would help an agent act on a 403.

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 takes zero parameters, so the baseline is 4 and there is nothing for the description to compensate for. The description correctly implies a no-argument diagnostic call by focusing entirely on the returned data.

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?

The description states exactly what the tool returns – the API key's granted scopes plus what each scope unlocks – which resolves the ambiguity of the opaque name 'whoami'. It does not explicitly contrast with any sibling, but no sibling tool overlaps this diagnostic function, so an agent can identify it without difficulty.

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 states when to call it (before attempting writes, or on a 401/403 scope error) and names the anti-pattern it replaces ('instead of retrying'). This is a genuine decision rule, not implied context.

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