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

Annotations already declare readOnlyHint=true, so the safe read-only nature is covered structurally. The description adds the useful detail that the id is a message id starting with 'AC' and maps to the REST endpoint GET /messages/{id}, but it says nothing about error behavior for unknown ids or pagination/return shape. That is a modest addition over the annotations.

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 compact clauses, front-loaded with the core action, with zero filler. Every element earns its place and is 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?

For a one-parameter read-only lookup with full schema coverage and readOnlyHint annotations, the definition contains everything needed to invoke it correctly. The only mild gap is that no output schema exists and the description does not hint at the returned message shape, though this is largely predictable.

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 single 'id' parameter is fully documented in the schema, including the 'AC' prefix. The description only restates that same prefix hint, adding no format or constraint details beyond the schema, 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 (get) plus resource (a single message) and even pins the identifier format, so it is clearly distinguishable from openphone_list_messages, which returns many messages. It stops short of explicitly naming a sibling as an alternative, so it is clear but not maximally differentiated.

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?

The description says what the tool does but never states when to reach for it versus openphone_list_messages or openphone_get_contact. There are no prerequisites, no conditions, and no exclusions stated.

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