render_template

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

Beyond the readOnlyHint annotation, the description discloses a critical behavior: unfilled placeholders remain literal and are listed in missingVariables. It also warns about the risk of sending literal {{placeholder}} text, which is valuable operational knowledge. This adds significant context beyond the annotation.

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 two sentences long, with the main action front-loaded. Every sentence earns its place, providing both the core functionality and a critical warning without redundancy.

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 there is no output schema, the description effectively communicates what to expect (rendered subject/body plus missingVariables). It also references the downstream send_email tool, placing this tool in the broader workflow. Despite lacking output schema, the description provides enough information for an agent to use it correctly.

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?

The schema already covers both parameters fully, so the baseline is 3. The description adds meaning to the variables parameter by explaining what happens when a placeholder is not provided (it stays literal and appears in missingVariables). This enriches the semantics beyond the schema's simple 'Map of variable name to replacement value'.

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 'render' and names the resource 'saved template's subject and body'. It clearly explains the substitution behavior and distinguishes this from simply retrieving a template (e.g., get_template). The resulting output is tied to a concrete use case (preparing content for send_email), which further clarifies its purpose.

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 on when to use this tool: before passing rendered content to send_email. It warns about the consequence of unfilled placeholders, which guides the agent to check missingVariables. However, it does not explicitly name alternative tools or state when not to use it, so a small gap remains.

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