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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the mutation risk is known. The description adds the key behavioral trait: omitted fields are preserved (partial update semantics), which is not visible in the schema or annotations. This is valuable context beyond the structured data.

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?

One short sentence that states the operation and the most important behavioral nuance. No wasted words, and the key partial-update semantics are front-loaded.

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 simple 4-param update tool with no output schema, the description plus annotations cover the essential context: what it does, that it's destructive, and that it's a partial update. It doesn't mention return values, but the absence of an output schema lowers that burden. It could note that id is required, but the schema already marks it required.

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 50%: body and subject have descriptions, while id and name do not. The description's partial-update note clarifies that all non-id fields are optional in effect, which adds meaning beyond the schema. However, it doesn't explain what 'name' represents or any constraints on id, so the description only partially compensates for the coverage gap.

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 action ('Update an email template') and the resource, which distinguishes it from create/delete/get/list siblings. It doesn't explicitly name a sibling alternative, but the verb+resource combination 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 implies a partial-update use case ('omitted fields keep their values'), which tells the agent when to use this over create (when the template already exists). However, it doesn't explicitly state when not to use it or mention alternatives like create_email_template or delete_email_template.

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