render_template

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

With no annotations provided, the description carries the full transparency burden. It explicitly discloses the key safety trait (no sending) and states the return fields. It does not discuss error behavior or side effects beyond sending, but for a preview tool the main risk is well covered.

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 a single, front-loaded sentence that communicates the primary action, the inputs, the outputs, and the crucial non-sending behavior. Every clause earns its place with no wasted words.

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?

The tool is simple with only two parameters and no output schema, but the description lists the returned fields and clarifies the no-send behavior, which is essential for safe selection. It could mention whether template_model is optional or what happens when it is omitted, but the schema already indicates it is optional, so the description is sufficiently complete.

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% for both parameters, so a baseline of 3 is appropriate. The description adds minimal extra meaning beyond the schema, referring to template_model as a 'variable model' and saying the template is rendered against it, but it doesn't elaborate on format, defaults, or edge cases.

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 uses a specific verb ('Preview') and resource ('stored template'), and clearly distinguishes this from sending tools by stating it renders without sending anything. It also names the exact return outputs (subject, html_body, text_body), making the tool's purpose unmistakable and differentiating it from siblings like send_email or send_email_with_template.

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 phrase 'without sending anything' clearly implies this tool is for previewing before sending, providing useful context for when to use it over the send-related siblings. It does not explicitly name alternative tools or state when not to use it, so it falls just short of a 5.

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