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

Annotations already cover readOnly/idempotent/non-destructive/closed-world, yet the description adds substantial context beyond them: deprecation and alias-window behavior, environment gating, the fact that the server chooses source/facility, unavailable vault, and required auth ('agent-scoped bearer key required; member/facility keys cannot impersonate an agent') plus scopes. This is rich behavioral disclosure that annotations cannot express.

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 critical routing information (deprecated, use get_inbound_item) is front-loaded, and most clauses earn their place via real behavioral constraints. Some trailing detail ('rollout switches... credential environment and SQL authorization are shared with REST') is dense internal jargon of marginal value to an agent caller, slightly diluting conciseness.

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?

With annotations covering the safety profile and an output schema documenting returns, the description only needs to convey deprecation, environment gating, and auth constraints — all of which it does. Nothing an agent needs to call this correctly 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?

Only one parameter (item_id) with 100% schema description coverage, so the schema already carries its meaning ('Inbound item id (UUID) from a list or search result'). The description adds no item_id syntax or format detail beyond the path reference ':id'. Baseline 3 is appropriate when the schema does the work.

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 states a specific verb and resource ('Read /v1/agent-inbox/:id/handling capabilities, version and history') and immediately signals its relationship to the sibling get_inbound_item via the deprecation note. An agent can tell exactly what this returns and that it is superseded.

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?

It names the replacement tool explicitly ('Deprecated: use get_inbound_item'), states when the alias still works (during the alias window), and constrains applicability ('private-mail Live and member-sample Sandbox workflow only; no generated fixtures or managed-PMB fallback'). The 'never substitute another key or mail API after denial' clause is an explicit exclusion.

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