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

Annotations already establish readOnly, idempotent, non-destructive, openWorld, so the safety profile is covered. The description adds genuine behavioral context beyond that: status only moves forward (monotonic, so polling is meaningful), failures always carry an error code, and only a subset of media/reaction failures include a corrective field hint.

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?

Short and front-loaded: the first clause names the tool's job and the possible outcomes before any caveats. The third sentence about retrying is useful but slightly editorial; overall little waste.

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?

An output schema exists, so return values need not be explained, and the description nonetheless characterizes the failure payload shape. For a two-parameter read-only lookup with high schema coverage, this is close to complete; only sibling routing guidance is absent.

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 100%, with message_id format and number_alias semantics fully documented in the schema. The description adds no parameter-level meaning, 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?

States a specific verb and resource (check a message's delivery stage) and enumerates the exact status values returned: queued, sent, delivered, read, failed. What is missing is differentiation from look-alike siblings such as get_message, get_message_receipts, and get_message_responses, which an agent must choose between.

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?

There is real guidance on interpreting results ('read the code before retrying, because most failures repeat identically'), but nothing on when to call this versus get_message_receipts or get_message. The when-to-use is only implied by the word 'status'.

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