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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the '[read]' prefix is redundant. The description does add value by naming the returned fields (no output schema exists), but it never explains what happens when both optional zone parameters are omitted — all zones, empty result, or error.

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?

A single dense sentence that front-loads the operation type and resource, then the identifier semantics, then the downstream hand-off. Slightly cluttered by echo fields in parentheses, but nothing wasted.

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 read-only list with no output schema, the description covers returned fields, zone scoping, and downstream usage. The only real gap is the undefined behavior when no zone identifier is supplied, which is the one thing an agent could plausibly get wrong.

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 0%, so the description must compensate. It does clarify that email_zone_id and email_zone_uuid are alternative identifiers for the same zone, which is the key semantic. However it does not state the params are optional-with-null-default or what the no-parameter behavior is, leaving the other half of the semantics to inference.

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-and-resource pair (list mailboxes) and immediately enumerates the returned fields (email_account_id, email_account_uuid, address, display name), scoping them to one e-mail zone. An agent can distinguish this from list_email_zones without opening the schema.

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?

Explicitly tells the agent what to do with the results: pass email_account_id or email_account_uuid onward to send_email / list_email_messages, which is genuine routing guidance. It does not explicitly contrast with list_email_zones or state exclusions, 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.