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

Annotations already declare readOnlyHint=true, so the read-only safety profile is covered. The description adds the REST endpoint mapping (GET /messages/{id}), which is mildly useful for groundedness, but says nothing about error behavior for missing/invalid ids or the shape of the returned message.

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 short sentences, front-loaded with the action and resource, no filler. Every clause carries 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 simple single-resource lookup with one fully documented required param and readOnlyHint covering safety, the description is essentially complete. Only the return-value/error behavior is unaddressed, which is minor given the tool's simplicity and lack of an output schema.

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% and there is only one parameter whose 'starts with AC' format is already documented in the schema. The description merely repeats that prefix hint, adding no new meaning beyond the structured field.

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?

Specific verb+resource: 'Get a single message by its id'. The word 'single' implicitly contrasts with the sibling openphone_list_messages, but the differentiation is not made explicit, so an agent must infer it.

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 by 'a single message by its id' — you would use it when you already have an id rather than listing. However, there is no explicit when-to-use statement, no mention of the list_messages alternative, and no note on where ids come from.

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