customerio_search_customersSearch/list people by a Customer.io filter (segment or attribute conditions). e.g. filter={"segment":{"id":7}} or {"and":[...]}. App API: POST /v1/customers.
| Name | Required | Description | Default |
|---|---|---|---|
| limit | No | Max people to return. | |
| start | No | Pagination cursor from a previous response's `next`. | |
| filter | Yes | Customer.io filter object, e.g. {"segment":{"id":7}} or {"and":[{"attribute":{"field":"email","operator":"exists"}}]}. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, and the description adds the underlying App API endpoint (POST /v1/customers) plus filter-query examples. It does not disclose pagination behavior or response characteristics, but the annotation covers the safety profile.
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: the first states purpose, the second gives filter examples, and the third provides the endpoint. Every sentence contributes information without redundancy or padding.
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 read-only search tool with one required nested object parameter, the description plus schema is nearly complete. It could be stronger with explicit pagination or response hints, but the schema already documents start as a cursor from a previous response's 'next'.
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 the baseline applies; the filter examples in the description largely mirror the schema's own examples. Limit and start are already documented in the schema, and the description adds no extra semantic detail for them.
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 states a specific verb ('Search/list') applied to people, with a concrete mechanism: a Customer.io filter of segment or attribute conditions. Worked examples make the tool's intent unmistakable, and it is clearly distinct from sibling tools like list_segments or get_customer_attributes.
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 description establishes a clear context: use this when you need people matching a Customer.io filter. It does not explicitly name alternatives or exclusion criteria, but the filter-based search context is enough to route most calls correctly.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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