MailSenpai

List Segment Subscribers

list_segment_subscribers

Read-onlyIdempotent

Returns the subscribers that currently match a saved segment (subscriber_uid, email, status, field values). Use list_subscribers for the whole list, or search_subscribers_by_custom_fields for a one-off filter without saving a segment. Paginated; read-only.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "list_uid": "<list_uid>",
      "segment_uid": "<segment_uid>"
    },
    "name": "list_segment_subscribers"
  }
}

Input Schema

Name	Required	Description
`page`	No	Page number to return, starting at 1.
`list_uid`	Yes	Unique ID of the mailing list (list_uid), a 13-character code such as "ab123cd456ef7". Find it with list_lists.
`per_page`	No	Results per page (default 10). The server caps it at the plan maximum, usually 50.
`segment_uid`	Yes	Unique ID of the segment (segment_uid). Find it with list_list_segments.

Output Schema

Name	Required	Description
`ok`	No	Whether the MailSenpai MCP operation succeeded.
`data`	No	Main MailSenpai API response payload, when available.
`error`	No	Machine-readable error name when the tool fails.
`result`	No	Alternative result payload for tools that return a named result.
`status`	No	Status returned by MailSenpai or by the MCP layer.
`details`	No	Additional diagnostic details, validation errors, API response body or nested metadata.
`message`	No	Human-readable message from MailSenpai or from the MCP layer.
`pagination`	No	Pagination metadata for list/search tools when returned by the MailSenpai API.
`rate_limit`	No	Rate-limit metadata when relevant.

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedOct 6, 2026

addedInput schema / properties / list_uid / description

Added value: +"Unique ID of the mailing list (list_uid), a 13-character code such as \"ab123cd456ef7\". Find it with list_lists."

addedInput schema / properties / page / description

Added value: +"Page number to return, starting at 1."

addedInput schema / properties / per_page / description

Added value: +"Results per page (default 10). The server caps it at the plan maximum, usually 50."

addedInput schema / properties / segment_uid / description

Added value: +"Unique ID of the segment (segment_uid). Find it with list_list_segments."

First observedOct 2, 2026

TDQS

A4.3/5.0

Behavior3/5

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, so 'read-only' in the description is redundant. The only added behavioral fact is 'Paginated' and the implication that membership is evaluated dynamically ('currently match'). Useful but thin against an annotation set that already carries 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.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, zero filler, with the scope/return summary front-loaded and the disambiguation trailing. Every clause earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists so return values need not be explained, annotations cover the safety profile, and the schema fully documents all four parameters. The description supplies the routing information that neither structured field provides, so nothing needed for correct invocation is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so page, per_page, list_uid and segment_uid are fully documented in the schema (including defaults, caps and how to find IDs). The description adds no parameter syntax or format beyond that, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Returns the subscribers that currently match a saved segment') plus the returned fields, and explicitly contrasts with list_subscribers and search_subscribers_by_custom_fields. An agent can distinguish it from all three related siblings without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Names both alternatives and the condition that selects each: list_subscribers for the whole list, search_subscribers_by_custom_fields for a one-off filter that isn't saved. This is explicit when-to-use/when-not routing.

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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