MailSenpai

Add or Update Subscriber

create_or_update_subscriber

Destructive

Upsert: looks up data.EMAIL in the list; if found it updates that subscriber, otherwise it creates a new one. Use it to sync contacts when you do not know whether they already exist. Existing values are overwritten, so confirm with the user before updating real contacts.

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>",
      "data": "<data>"
    },
    "name": "create_or_update_subscriber"
  }
}

Input Schema

Name	Required	Description	Default
`data`	Yes	Subscriber data keyed by field tag; EMAIL is required, e.g. {"EMAIL": "jane@example.org", "FNAME": "Jane", "LNAME": "Doe"}. Optional: status, source, ip_address.
`list_uid`	Yes	Unique ID of the mailing list (list_uid), a 13-character code such as "ab123cd456ef7". Find it with list_lists.

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.

Changed2 schema fields changedOct 6, 2026

addedInput schema / properties / data / description

Added value: +"Subscriber data keyed by field tag; EMAIL is required, e.g. {\"EMAIL\": \"jane@example.org\", \"FNAME\": \"Jane\", \"LNAME\": \"Doe\"}. Optional: status, source, ip_address."

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."

First observedOct 2, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already flag destructiveHint=true and idempotentHint=false, but the description adds genuinely useful context beyond them: that existing values are overwritten and that the user should confirm before touching real contacts. It does not describe partial-vs-full overwrite semantics or error behavior when list_uid is invalid, so it is strong rather than complete.

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?

Three short sentences, front-loaded with the upsert behavior, then usage context, then the overwrite warning. No filler and nothing important buried at the end.

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

Completeness4/5

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 no explanation, and the annotations cover the safety profile. The description supplies the lookup key, the overwrite risk, and the usage condition. Only edge cases (nonexistent list_uid, invalid EMAIL) are unaddressed, which is acceptable for this complexity.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3, but the description adds meaning the schema does not: EMAIL is the matching key used for the lookup, not merely a required field. That clarifies the upsert mechanics in a way the schema alone leaves implicit.

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?

The description states a precise verb and mechanism: it looks up data.EMAIL in the list and updates or creates accordingly. This upsert framing clearly distinguishes it from the sibling create_subscriber and update_subscriber, which an agent can tell apart without opening schemas.

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

Usage Guidelines4/5

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

"Use it to sync contacts when you do not know whether they already exist" gives an explicit when-to-use condition, and the warning to confirm before updating real contacts adds a usage constraint. It stops short of naming the alternatives (create_subscriber, update_subscriber) that a reader would want for the known-existence case.

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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