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

readOnlyHint=true already tells the agent this is a safe read, so the description only needs to add beyond that. It contributes the caller-identification framing and the underlying endpoint, but says nothing about result behavior (e.g., partial matches, empty results, or the 50-number cap's effect).

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, front-loaded sentences with no wasted prose; the purpose comes before the endpoint citation. The raw 'POST /v3/customer/phone_number/search' reference is boilerplate rather than agent-facing signal.

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?

With no output schema, the description should ideally convey what comes back (a list of matching customers, possibly empty). It covers the input side adequately and the read-only nature is annotated, but the return shape remains unspecified.

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 both parameters are already documented in the schema, establishing the baseline of 3. The phrase 'any of the given phone numbers' usefully implies OR-matching across the array, but the excludeCustomerId filter is not elaborated on in the description.

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 ('find') plus resource ('customers') and the identifying key ('phone numbers'), so the operation is unambiguous. It does not explicitly contrast with the very similar siblings shopmonkey_find_customers_by_email and shopmonkey_search_customers, leaving the differentiation to the agent.

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 usual way to identify a caller' hints at the intended scenario (inbound caller lookup), which is useful context. However, there is no stated when-not-to-use or explicit routing to the email-based or general search siblings.

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