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

readOnlyHint=true already declares the safe-read profile, so the description's added value is limited to naming the lookup keys and the returned field groups. It omits behavior for a missing/invalid contact (error semantics) and rate limits, leaving the annotation to carry safety.

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 tight sentences; the core ('Get a single contact by id or phone number') is front-loaded, followed by returned fields. The trailing REST endpoint restatement is mildly redundant but harmless.

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 single-parameter read tool with annotations covering safety and no output schema, the description adequately covers what is fetched and what comes back. Only error/not-found behavior is unaddressed, a minor gap.

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 the single 'contact' parameter as 'Contact id or phone number.' The description repeats this without adding format, validation, or fallback detail, so 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 ('Get') and resource ('a single contact') with lookup key ('id or phone number') and enumerates returned content (profile fields, list memberships, custom fields). It distinguishes itself from list_contacts only implicitly via 'single,' without naming the alternative.

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 word 'single' implies use when fetching one known contact versus the sibling list_contacts, but there is no explicit when-to-use, when-not, or named alternative. Usage is inferred rather than stated.

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