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

Annotations already establish the safe read-only profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false). The description adds meaningful beyond-annotation behavior: the response is HTML, an absent signature yields no signature rather than an error, and the operation is unsupported for Outlook mailboxes.

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 tightly written sentences with zero filler. The core purpose is front-loaded, followed immediately by the edge case and the provider limitation.

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?

An output schema exists, so return-value structure need not be explained. Given the simple one-parameter read operation, the description covers the essential context: provider support, output format, and empty-signature behavior.

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%, so the single mailbox parameter is already fully documented as a name or email address. The description adds no syntax, format, or constraint details beyond the schema, 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?

States a specific verb (Read) and resource (signature on the mailbox's own send-as identity), and the 'Gmail mailboxes only' caveat distinguishes it from the broader settings family. The sibling settings_send_as_patch is implicitly the write counterpart, so the read-only purpose is clear without ambiguity.

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?

Gives a clear usage condition and exclusion: it works only for Gmail mailboxes, since Outlook exposes no signature. However, it does not explicitly name the natural alternative for changing a signature (settings_send_as_patch) or otherwise route the agent to the correct sibling tool.

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