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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds useful context about what is returned (default fields such as name, company, role, emails, phone numbers plus custom fields), but says nothing about error behavior for invalid ids 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?

Two compact sentences, with the operation and scope front-loaded and return-field detail appended. The REST endpoint reference is mildly redundant but harmless; nothing is padded.

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 read with annotations covering safety and a fully documented one-parameter schema, the description is nearly complete, even enumerating the return envelope since no output schema exists. Only failure modes and auth requirements are unaddressed.

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% with a single required 'id' parameter already documented in the schema. The description restates 'by its id' without adding format, prefix, or lookup semantics beyond what the schema provides, 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?

The description names a specific verb and resource ('Get a single contact by its id') and enumerates the returned default fields plus custom fields. It distinguishes itself from openphone_list_contacts by scoping to one contact, though it never explicitly names that sibling.

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 singular, id-based retrieval pattern, but there is no explicit statement of when to use this versus openphone_list_contacts or openphone_get_contact_custom_fields. No prerequisites or exclusions are given.

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