render_template

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

Annotations already indicate read-only, idempotent, non-destructive. Description adds behavioral context: details auto-population logic with message_id (fields like recipient_name, recipient_email, etc.) and the override rule for vars. Consistent with annotations, adds value beyond them.

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?

Four sentences, front-loaded with main purpose, no fluff. Each sentence adds specific, useful information. Efficient and well-organized.

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's moderate complexity and the existence of an output schema (which covers return format), the description is complete. It covers purpose, side-effect-free nature, auto-population, override behavior, and integration with sibling tools. No gaps.

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% (all parameters have descriptions). Description adds meaning beyond schema: explains how message_id triggers auto-population of certain template variables, and that vars override auto-fills. This contextual usage info is valuable.

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?

Explicitly states 'Render a template into ready-to-send subject and body text' with a specific verb and resource. Clearly distinguishes from sibling tools like create_draft by noting that the caller must pass the output to create_draft or update_draft.

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?

Provides clear context for when to use message_id (reply context) and states no side effects. Explicitly says the caller is responsible for passing rendered text to create_draft/update_draft, differentiating from those tools. Lacks explicit 'when not to use' but covers key scenarios.

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