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

Annotations provide only a title, so the description carries the burden for behavioral disclosure. It implies that passing a tag creates a separate 'you+tag' address, but never explicitly states whether this is a mutation or if there are other side effects. It also doesn't confirm whether the untagged call is read-only.

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 a dense, two-sentence block with a colon and em dash, making it less scannable. It packs a lot of information, but could be better structured by separating the info-return part from the tag-workflow part.

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?

The tool is simple with one optional parameter and no output schema. The description covers the returned data (handle, email address, external mail availability) and the tag workflow, but 'How to reach the caller here' is ambiguous about the context, and no output format is provided.

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 schema only describes tag as 'A label for this handle', but the description adds meaning by explaining the you+tag pattern and how the resulting address is used with mail_inbox(tag). This goes beyond the schema description and clarifies the purpose of the optional parameter.

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 lists what the tool provides: the handle, email address (if mail domain exists), and external mail deliverability. This distinguishes it from siblings like mail_inbox or mail_send, though the phrasing 'How to reach the caller here' is somewhat awkward.

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?

It gives a workflow hint by suggesting 'Pass a tag for a separate one... then read only its messages with mail_inbox(tag)', which implies when to use a tag and directs to an alternative for reading. However, it lacks explicit 'when to use' / 'when not to use' guidance relative to other mail tools.

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