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

Beyond the destructiveHint annotation, the description discloses that this adds a persistent record and that emails/phoneNumbers are stored under default field labels — a real behavioral trait. It stops short of stating auth requirements, duplicate handling, or rate limits.

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 sentences, front-loaded with the core action and followed by the write warning and a storage detail. The REST endpoint line is mildly redundant given the tool name but is cheap and informative.

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 9-parameter write tool with no output schema and only a destructiveHint annotation, the description covers the mutation semantics adequately but omits the return value (created contact id), error/duplicate behavior, and permission requirements.

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%, so the schema already documents all nine parameters and their types. The description adds only a marginal note on how emails/phoneNumbers arrays are stored, which does not materially extend 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 ('Create a new contact in the workspace') plus the concrete side effect and backing endpoint (POST /contacts). This clearly separates it from the read-oriented siblings openphone_get_contact and openphone_list_contacts.

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 the create semantics and the 'WRITE ACTION' framing, but there is no explicit when-to-use guidance, no mention of how to handle existing/duplicate contacts, and no named alternative for read or update flows among the many sibling tools.

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