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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely new context that annotations cannot express: the `full_access` API key requirement, plus the concrete endpoint and operationId for tracing. It does not describe error behavior (e.g. 404 on missing id), which keeps it below a 5.

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 short sentences, zero filler, and the purpose is front-loaded before the auth and endpoint details. Nothing could be removed without losing information.

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 one-parameter read tool with full annotation coverage and no output schema, the definition gives everything needed to call it: purpose, required credential, and endpoint. The residual gap is the return shape and missing-id behavior, which an agent must guess, but this is minor for a trivial fetch.

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 the single `id` parameter is documented as a uuid, so the schema carries the load. The description's `GET /emails/{id}` adds the useful detail that the id is a path parameter, but nothing about form or lookup semantics beyond that — baseline 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?

States a specific verb ('Retrieve') and resource ('an email'), so the operation is unambiguous, and the endpoint `GET /emails/{id}` confirms it is a single-record fetch. It never distinguishes itself from the closest sibling `list_emails`, leaving the agent to infer that this one requires an id and returns one email.

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?

Usage is only implied by the required `id` parameter and the `/emails/{id}` path — the agent can reason that this is for fetching a known email rather than enumerating. There is no explicit statement of when to prefer this over `list_emails`, nor any note about what happens if the id is unknown or belongs to a different tenant.

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