mark_email_unread

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

With no annotations provided, the description carries the burden of behavioral disclosure. It discloses both the success return ('Returns a success confirmation') and the error condition ('Returns an error if the email ID does not exist'), and implies reversibility by naming the reverse tool. It does not cover idempotency or permissions, but for a simple mutation this is a solid level of transparency.

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 three sentences, each earning its place: purpose, use case, return/error behavior, and reversal instruction. It is front-loaded with the primary purpose and contains no filler.

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 single-parameter mutation with no output schema, the description covers the essential context: what it does, when to use it, the success/error behavior, and how to reverse it. No critical information is missing.

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%, and the schema already fully describes the parameter (type, range, description, and example source). The tool description adds no additional parameter-specific meaning, so the baseline 3 is appropriate.

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 clearly states the action ('Mark an email as unread') on the resource ('in Outlook') with a specific verb and resource. It also distinguishes itself from siblings by mentioning 'restore the unread indicator' and explicitly naming the reverse tool, mark_email_read.

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?

Provides a clear use case ('Use this to restore the unread indicator on a message') and explicitly names the alternative/reverse action ('Use mark_email_read to reverse this action'). This gives the agent actionable guidance on when to choose this tool over its sibling.

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