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 safety profile is supplied structurally. The description adds nothing beyond that: it doesn't clarify what a 'contactable inbox' is, whether the contact must exist, or the shape/pagination of the returned list.

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 definition is short but consists of two redundant sentences that say the same thing twice. Neither sentence earns its place, and the repetition front-loads no useful 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 read-only lookup with annotations covering safety and a fully documented schema, the description still leaves the core concept ambiguous — 'contactable inboxes' could mean inboxes the contact belongs to or inboxes that can contact them. Given no output schema, the description should carry this meaning but does not.

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%, with both parameters ('id' = ID of the contact, 'fields' = optional field selection) fully documented in the schema. The description contributes no syntax, format, or filtering semantics beyond that, so the baseline of 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?

The description is a tautology: 'Get Contactable Inboxes. Get List of contactable Inboxes.' repeats the name/title twice with no additional detail. The only added information is the plural 'List', which weakly implies a collection return, but nothing distinguishes it from siblings like get_inbox, list_inboxes, or get_inbox_members.

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 when-to-use guidance is given, and no alternatives are named despite many closely related siblings (get_inbox, get_inbox_members, list_inboxes). The agent gets no signal about when this tool is the right choice versus those.

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