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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description goes further, disclosing return-shape behavior that annotations cannot: outbound messages echo quick_replies/buttons/card, and inbound tap messages carry tapped_action with kind/payload/title — genuinely useful context since no output schema exists.

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 sentences, zero filler, with the core action front-loaded ahead of the supporting return-value detail. Efficient and easy to scan.

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 no output schema, the description steps in to describe notable return content, which is the right call for a single-item getter. It omits error behavior (e.g., unknown identifier) but is otherwise sufficient for correct invocation.

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% and the message_id field already documents 'Message hashid OR external_id'. The description restates this, only marginally sharpening it with the 'Postproxy hashid' qualifier, so it adds little beyond the schema. 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 and resource ('Get a single message') and enumerates the two accepted identifiers (Postproxy hashid or external_id). The 'single message' scope implicitly separates it from dm_messages_list, though it never names a sibling explicitly.

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 implied rather than stated: the agent infers it should call this when it already holds a message identifier. There is no guidance on when to prefer dm_messages_list versus this tool, and no mention of prerequisites or paging context.

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