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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so 'Nothing is saved' is reinforcement rather than new information. The genuinely additive disclosure is 'spends one AI action' — a quota/cost trait the agent cannot get from structured fields — plus the output length cap of 100 characters. It stops short of saying how many suggestions come back or how style is sampled.

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 front-loaded sentence: purpose first, then output constraint, style source, safety and cost. Every clause carries distinct information and nothing is repeated from the annotations verbatim beyond the brief 'Nothing is saved' reinforcement.

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, the description does the necessary work of describing the return value (a subject line under 100 characters) and the quota cost. The remaining gap is whether one or multiple suggestions are returned and what exactly the 'message' input should contain, which matters for a tool whose only input is that field.

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 0%, so the description carries the burden, and it only obliquely identifies the single required 'message' parameter as the email body. That does disambiguate subject-vs-body-vs-recipient, but it adds nothing about whether the input may include an existing subject, formatting, or the 100k character ceiling.

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 artifact: 'Suggest a short subject line for the body of an email', with the extra constraints of <100 characters and workspace style. It is distinguishable from neighbors like rewriteEmail or getReplySuggestions, though it never names an alternative explicitly.

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 implied by 'for the body of an email' and 'in the style of the mail this workspace has sent', which tells the agent the input context needed. There is no explicit when-to-use / when-not, and no guidance versus sibling tools that also produce email text (rewriteEmail, getReplySuggestions).

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