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

Annotations already indicate a mutating operation, but the description adds meaningful behavioral detail: partial update semantics (omitted fields unchanged), clearing behavior via null, unlink semantics, immutability of the email address, and the master key requirement. This is exactly the kind of context an agent needs beyond the raw schema.

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?

Two sentences, no filler. The first sentence front-loads the operation and target fields; the second compactly conveys clear/omit semantics, the immutability constraint, and the access requirement. Every sentence 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?

For a simple three-parameter update tool with a complete schema, a clear output schema, and annotations covering mutation/idempotency, the description provides the essential additional context: partial update behavior, clearing behavior, email immutability, and required access level. Nothing critical is missing.

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 schema already documents each parameter with null vs. omit semantics. The description restates these semantics rather than adding new parameter-level meaning. It does clarify the overall purpose of the update and the unlink/remove behavior, but that is more purpose-level than parameter-level.

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 names the resource ('inbox') and specific verb ('update'), and immediately scopes what can be changed ('display name or agent association'). It also states what cannot be changed ('The email address itself cannot be changed'), disambiguating from other inbox operations like inbox_create, inbox_delete, inbox_get, and inbox_list.

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 clearly conveys when to use the tool: to modify an existing inbox's display name or agent association. It provides usage details about null vs. omitted fields and notes the master key access requirement. It does not explicitly name alternative tools for creation or deletion, 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.