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

Annotations already indicate readOnlyHint=false, and the description confirms mutation. It adds the partial-update behavior (only provided fields change), which is useful context beyond the schema. However, it does not disclose error handling, idempotency, or any side effects on other resources, so it only partially covers behavioral disclosure.

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, front-loaded sentence with no filler. It efficiently communicates the core behavior (partial update) in minimal words. It could be slightly more explicit about usage context, but as a concise definition it earns its place.

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 simplicity and the presence of an output schema and full parameter descriptions, the description is adequate for a basic update operation. It lacks details on error scenarios, validation rules, or whether the update is atomic, but for a straightforward mutable operation with 100% schema coverage, it covers the essentials.

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 has 100% description coverage for all 8 parameters, so the baseline is 3. The description adds the semantic that only specified fields are updated, reinforcing the partial-update intent. It doesn't add per-parameter detail, but that's already in the schema, so this is adequate.

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 verb (update), resource (sender), and implies a partial-update semantic ('only the fields you want to change'). It is distinct from create/delete senders, though it doesn't explicitly name sibling alternatives. The purpose 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?

No guidance is provided on when to use this tool versus alternatives like create_email_sender or delete_email_sender. The context of 'update' is implied but not contrasted with creation or deletion, leaving the agent to infer the appropriate scenario.

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