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

readOnlyHint=true already declares this is a safe read. The description adds return-field context (text, direction, status, timestamps), which is useful, but says nothing about pagination behavior, rate limits, or result ordering despite pageToken/maxResults existing. With annotations carrying the safety profile, this is adequate but not rich.

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?

Three short, front-loaded sentences with no filler; the core scope comes first, followed by return values and the REST mapping. Tight overall, though the REST endpoint sentence is mildly decorative for an agent.

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 read-only list tool with full schema coverage, the definition covers purpose, scope, and return fields. The absence of an output schema is partly compensated by the field list, but pagination guidance is left entirely to the 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 description coverage is 100%, so all seven parameters, including formats like E.164 and ISO-8601, the 1-100 range, and cross-references to sibling lookup tools, are already documented in the schema. The description adds no parameter meaning beyond it, so the 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 (List) and resource (messages) scoped to a conversation between an OpenPhone number and participants, and even names the return fields and REST endpoint. It does not explicitly distinguish itself from siblings like openphone_get_message or openphone_list_conversations, so it falls short of a 5.

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 phrase 'in a conversation between one of your OpenPhone numbers and one or more participants' implies when to use it, but there is no explicit guidance on alternatives (e.g. get_message for a single message) or when not to use it. Usage is implied rather than stated.

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