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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuine context beyond that: the exact fields returned (id, name, signing mode, AI disclosure preset, preview), the default ('me'), and the non-obvious scoping caveat that 'A connection bound to one agent lists only that agent.'

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?

Three sentences, front-loaded with the purpose and the returned fields before the handoff instruction; nothing is filler. The parenthetical qualification about company agents ('agents of a company they own or that acts for them') is dense but load-bearing, keeping it just short of maximal conciseness.

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 no output schema and no parameters, the description correctly compensates by summarizing the return payload and the default and scoping rules. Combined with annotations that cover the read-only/idempotent profile, an agent has what it needs to call this correctly and chain into get_signature; only explicit exclusion guidance against sibling list tools is absent.

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 tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The description uses the space instead to explain what the returned signature identifiers feed into (get_signature), which is the relevant 'parameter' concept here.

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 and resource ('Lists the signatures'), defines the scope precisely ('the signed-in person can send email with'), and enumerates the three signature classes (own, AI assistants', company AI agents'). It also names the sibling it hands off to (get_signature), so the agent can distinguish it from get_signature and create_signature without reading any 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?

Explicitly routes the follow-up step: 'Pass a choice as signature to get_signature,' and adds the escalation rule 'If it is unclear which one the person wants for an email, ask them before sending.' That is clear when-to-use guidance and names the alternative, though it never states when not to use this tool instead of, say, list_members or list_templates.

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