Who am I

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, covering safety and idempotency. The description adds value by explaining the operational rationale (confirming the mailbox identity before actions), which is beyond the structured metadata. It doesn't detail potential edge cases, but for a simple read-only look-up, this is adequate given annotation coverage.

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 sentence that front-loads the action and output, then gives usage context. No filler or redundancy; every word earns its place. Ideal for quick scanning by an agent.

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, read-only identity tool with no output schema, the description is complete: it states what is returned and when to use it. There is no missing information an agent would need to invoke it correctly. The tool's simplicity means the description fully covers operational needs.

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 schema needs no description. The description usefully lists the exact fields returned (display name, UPN, id), which helps an agent understand the output even without an output schema. With schema coverage at 100% (trivially) and no params, the baseline of 4 applies, and the description adds relevant info about return values.

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 a specific verb ('Return') and resource ('signed-in mailbox's identity') with concrete output fields (display name, user principal name, id). It also signals a unique purpose—confirming which mailbox the server is on—that distinguishes it from sibling operations like list_folders or get_message.

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 advises using the tool 'before reading or writing,' giving a clear contextual trigger. It doesn't enumerate alternatives or when-not-to-use, but as a standalone identity check, it competes with no sibling tool, so the guidance is sufficient for an agent to know when to call it.

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