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

The description explicitly states 'no external research or outbound actions', but the annotation openWorldHint is true, which typically indicates the tool may access external data. This is a direct contradiction. Additionally, the description mentions payment authorization and returns a draft, but the contradiction with the annotation undermines transparency.

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?

The description is concise, with three sentences covering purpose, constraints, and payment. However, it front-loads the purpose but then mixes constraints and payment details without a logical structure. It is not verbose, but the information is not optimally organized for quick scanning.

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?

Given the tool has 5 parameters including a nested input object, no output schema, and contradictory annotations, the description is inadequate. It omits parameter explanations, result format details, and clear payment mechanics beyond a mention. The tool is complex enough that a more thorough description is required.

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 0%, and the description provides no information about any of the parameters (e.g., 'brief', 'source_text', 'audience', or the signature fields). The description only references 'the supplied offer' without mapping to the schema, leaving agents with no guidance on what to fill in.

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 clearly states the tool generates email subject lines and preview text, grounded in the supplied offer. It specifies the resource ('email subject lines') and the action ('generate'). However, it does not explicitly differentiate from sibling tools like 'headline_variants' or 'ad_copy', though the email-specific focus helps.

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?

The description implies usage context: 'grounded in the supplied offer' and 'Uses buyer-supplied information only' suggest it is for creating subject lines from provided materials. It does not state when to avoid this tool or mention alternative tools, leaving the agent to infer from the name and siblings.

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