render_template

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

With no annotations provided, the description carries full burden. It explicitly states 'No side effects,' discloses auto-fill behavior (recipient_name, recipient_email, etc.), and the precedence rule 'User-supplied vars always override auto-fills on conflict.' This covers the main behavioral traits an agent needs, though it omits error handling or edge cases.

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 approximately 90 words across three paragraphs, with each sentence contributing value. It front-loads the primary purpose, then side-effect caveat, then parameter behavior. No redundancy or filler; well-structured.

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 has an output schema, so return values need not be described. The description covers purpose, side effects, parameter semantics, and next steps. It does not mention error conditions (e.g., missing template), but given the output schema and other disclosures, it is largely complete for correct invocation.

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%, but the description adds significant meaning beyond the schema. It explains exactly how message_id triggers auto-population of four variables and how vars interact with auto-fills, including the override precedence. This is critical semantic information not present in the parameter descriptions.

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 it 'Render a template into ready-to-send subject and body text.' This specifies the verb (render), resource (template), and output. It does not explicitly contrast with sibling tools like get_template or save_template, but the purpose is unambiguous.

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 provides clear context: 'No side effects — caller is responsible for passing the rendered text to create_draft or update_draft.' It also explains when message_id is useful. However, it does not explicitly state when not to use this tool or name alternatives, relying on implicit understanding from the sibling list.

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