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

Annotations already declare the mutation/safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=false), so the bar is lower. The description adds a genuine authorization trait not present in structured data – grant-scoped connections can only route to their own mailboxes – though it says nothing about duplicate-alias conflicts, verification of destinations, or return behavior.

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 tight sentences with zero filler. The core purpose and an example address are front-loaded, and the permission caveat follows where it is easy to catch before invocation.

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-required-parameter create tool with no output schema, the description covers purpose, scope limit and an authorization constraint. It omits error/conflict behavior and whether destinations must be pre-verified, which are minor gaps given the schema carries all field-level detail.

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 coverage is 100% and all three parameters carry their own descriptions with type, pattern and length constraints. The description's only parameter-adjacent detail, the 20-destination cap, merely restates the schema's maxItems, so it adds no meaning beyond structured fields (baseline 3).

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?

States a specific verb (Create) and resource (alias), and immediately disambiguates the resource by defining it as a forwarding address rather than a mailbox, which separates it from create_mailbox/create_draft siblings. It stops short of naming the sibling tools explicitly, so it is clear but not maximally differentiating.

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?

Provides real context: the alias is for forwarding and the grant-scoped restriction tells the agent when a route is valid ('may only route to their own mailboxes'). It does not explicitly say when to choose an alias over a mailbox or draft, so alternatives are left implicit.

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