Display Message

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

Annotations already declare readOnlyHint=false and idempotentHint=false, but the description explains why: "It changes the user's screen, and Thunderbird may mark the message read." That side-effect disclosure (read-state mutation) is genuinely additive context an agent could not infer from the hints. It stops short of covering failure behavior (e.g., invalid or missing messageId/folderPath), which keeps it off a 5.

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?

Two compact sentences with the primary action and mode options front-loaded, followed by the usage rule and the side-effect caveat. Every clause carries information; there is no filler or repetition.

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 three-parameter, non-destructive display tool with full schema coverage and annotations, the description covers purpose, alternative, and side effects. The only minor gap is what happens when the message or folder cannot be found, which is a small omission given no output schema exists.

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 enum for displayMode already documents '3pane' as default, 'tab' and 'window'. The description only echoes the default mode and adds no format or derivation detail beyond the schema's "from searchMessages" hints, 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?

"Show a message to the user in Thunderbird" names a specific verb and resource, then immediately specifies the surfaces (3pane mail view by default, or tab/window). It also distinguishes itself from getMessage, so an agent can tell display-vs-read apart without opening either schema.

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?

"Use it when the user should look at it; to read it yourself, getMessage" gives an explicit when-to-use rule and names the exact alternative tool with the condition that selects it. Nothing is left to inference.

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