apply_template

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

The annotations (readOnlyHint=false, destructiveHint=false) indicate the tool performs actions but is not destructive. The description adds behavioral transparency by disclosing the specific side effects of each action: preview (no side effect), draft (saves a draft), and send (sends immediately). This goes beyond the annotations, though it does not cover other factors like rate limits or authentication requirements.

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, front-loaded with the purpose, and contains zero unnecessary words. Every sentence contributes to understanding the tool's function and actions. This is exemplary conciseness.

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?

For a tool with 5 parameters, an enum, and a nested object, the description plus high-quality schema descriptions cover the core functionality. It explains the three action modes and their implications. The lack of an output schema is compensated by the description's focus on actions. However, it does not mention possible errors, return formats, or prerequisites beyond what the schema states, preventing a perfect score.

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 input schema covers 100% of the parameters with descriptions, including the default and enum values for 'action.' The description adds marginal value by explaining the meaning of each action, but this is largely a restatement of the schema's own descriptions. It does not introduce new parameter-level details, so the baseline of 3 is appropriate.

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's function: 'Apply an email template with variable substitution.' It also enumerates the three actions (preview, draft, send), which distinguishes it from sibling tools like send_email or save_draft, which lack template substitution. The verb 'apply' plus the resource 'email template' is specific and 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 usage context by explaining each action: 'Use action "preview" to see the result, "draft" to save as draft, or "send" to send immediately.' This tells the agent when to choose each action. However, it does not explicitly mention when not to use this tool or alternatives, so it falls 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.