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

With no annotations, the description carries the behavioral burden and largely meets it: it discloses the identity source (OAuth bearer sub/iss or verified end_user_assertion), the output shape, and the null behavior. It stops short of explicitly stating there are no side effects or rate-limit/auth failure behaviors, but the passive 'carries' wording strongly implies a read-only query.

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?

A single dense sentence front-loads the core result ('the end user this call carries') and then packs the source, fields, and null case without 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 zero-required-parameter introspection tool with no output schema, the description is complete: it explains what the agent will get back, the exact fields, the null case, and the one optional parameter is fully documented in the schema.

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 100%, so the schema already documents tenant_key, including the bearer-header precedence. The tool description itself adds no parameter semantics beyond the schema, so the baseline 3 applies.

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 identifies the tool's subject precisely: the verified end-user identity carried on the current call, with the exact fields it contains and a null fallback. It does not use an explicit action verb like 'return' or 'get,' but 'whoami' plus the description makes the purpose unambiguous.

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?

The description implies when to use this tool: when you need the end-user identity attached to the current call, and it notes the no-identity case. It does not explicitly distinguish this from sibling tools like host.whoami or host.agent.whoami, nor give exclusion criteria.

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