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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds useful context that this read is executed as POST /v1/customers, but it says nothing about result volume, pagination continuation behavior, or rate limits, so it only modestly exceeds what the annotations provide.

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: what it does, the filter shape with a concrete example, and the underlying endpoint. Every element earns its place with no redundancy.

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 filtered search with a readOnly annotation and no output schema, the definition conveys the filter contract well. It omits what the response contains (list of people plus a next cursor), which is a minor gap given no output schema is present to cover it.

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% and the schema itself already documents limit, start (cursor from a previous response's next), and the filter object with the same example shape used in the description. The description largely restates schema content, 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 and resource ('Search/list people') plus the scoping mechanism (a Customer.io filter with segment or attribute conditions), which separates it from sibling list/get tools returning campaigns, messages, or segments. It does not explicitly name or rule out a sibling, so it falls just short of 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?

Usage is implied through filter examples ('filter={"segment":{"id":7}}'), which tell the agent the tool is for conditional lookups, but there is no explicit when-to-use or when-not guidance, nor any pointer to alternatives like get_customer_attributes or list_segments for non-filtered retrieval.

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