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

Annotations already indicate this is a write operation (readOnlyHint=false) and not destructive (destructiveHint=false). The description adds the key behavioral detail that only provided fields are updated, which is not conveyed by the annotations. This goes beyond the structured data and is valuable for the agent. No contradiction with annotations.

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 concise sentence that is front-loaded with the action and resource, and it adds the key partial-update behavior without waste. Every word earns its place, and it is easy to parse quickly.

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 mutation tool with six parameters and an output schema, the description covers the core purpose and the important partial-update semantics. The output schema handles return value details, and annotations cover safety. The description could mention any prerequisites (e.g., the template must exist) but the schema hints at that via the id description. Overall, the information is sufficient for correct invocation, though slightly more context on expected behavior after update could be added.

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 description coverage is 100%, and the description does not add any parameter-specific semantics beyond what the schema already provides. The schema's descriptions for each parameter (e.g., 'Template ID (from list_email_templates)') are adequate. The description's mention of partial updates is more of a general behavior than per-parameter clarification, so the baseline of 3 applies.

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 states a clear action ('Update') on a specific resource ('email template') and adds the nuance 'only the fields you want to change,' which distinguishes it from create/delete operations and clarifies the partial-update nature. This is specific and differentiates it from siblings like create_email_template and delete_email_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 description implies usage for modifying an existing template but does not explicitly state when to use it over alternatives or when not to use it. It mentions the partial-update behavior, which is a usage hint, but there is no explicit guidance about prerequisites, fallback tools, or exclusion conditions. Given the sibling list includes update_template (generic), the description could have clarified the email-specific scope.

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