open_in_mail

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

The phrase 'on the user's screen' usefully discloses that this triggers a visible client-side action, which explains why readOnlyHint is false despite the read-like verb. Beyond that, it says nothing about whether Mail must be running, what happens if the id is stale, or whether focus is stolen from the user's current work.

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 with zero filler, and the key qualifier ('on the user's screen') is placed where it is read first. Nothing is redundant.

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?

With one fully documented parameter and an output schema present, the tool is simple enough that the short description is close to sufficient. The remaining gap is routing: without any mention of read_mail or search_mail as the source of the id, an agent has to work out the workflow from sibling names alone.

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 description coverage is 100%, and the id parameter already documents 'Message id from search_mail results.' The description adds no additional meaning about the identifier or its expected format, so the baseline of 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 states a specific verb and resource: 'Open a message in Mail'. An agent can tell this is a UI-launch action rather than a data fetch. It does not, however, name or contrast with the closest sibling, read_mail, which retrieves message content.

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?

Usage is only implied: open a message so the user can see it on screen. There is no explicit guidance on when to prefer this over read_mail for reading content, nor any prerequisite or exclusion stated. The agent must infer that this is for user-facing presentation rather than content retrieval.

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