Ballast - Cold Email

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label_thread

Set or clear a thread's label to trigger campaign actions such as suppress, stop, pause, or move the lead to a list; null removes it.

Instructions

Set or clear a thread's label The lead gets the label for the thread's campaign and the label's triggers run (suppress, stop in campaign, pause campaign, move to list). null clears it.

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": {
      "id": "<id>",
      "labelId": "<labelId>"
    },
    "name": "label_thread"
  }
}

Input Schema

Name	Required	Description	Default
`id`	Yes
`labelId`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 21, 2026

TDQS

A3.5/5.0

Behavior4/5

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

With no annotations, the description carries the full burden and does meaningful work: it discloses that the lead gets the label for the thread's campaign and that the label's triggers fire (suppress, stop in campaign, pause campaign, move to list). That is real side-effect disclosure. It still omits permission requirements and reversibility.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

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

Compact and front-loaded with the core action, but it has a run-on structure and a missing sentence break ('a thread's label The lead...'), and 'null clears it' partially restates the 'or clear' already in the opening clause.

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?

With no output schema and no annotations, the description still conveys the essential mutation semantics and its cascading side effects, which is the critical information for a write tool. It stops short of documenting permissions, error behavior, or what the call returns.

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 coverage is 0%, so neither parameter is documented in the schema. The description compensates for labelId by explaining that null clears the label and by describing the tool's effect on the lead; however, the 'id' parameter (presumably the thread ID) is never explained, leaving half the parameters unaddressed.

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

Purpose4/5

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

States a specific verb pair and resource: 'Set or clear a thread's label.' This is clear and distinguishable, but it does not contrast itself with any sibling tool (e.g. pause_campaign, add_suppressions) even though the described trigger effects overlap with those siblings.

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

Usage Guidelines2/5

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

The description explains how to clear ('null clears it') but gives no guidance on when to use this tool versus siblings like pause_campaign or add_suppressions, which perform some of the same downstream actions. Usage context is only implicitly derivable from the trigger list.

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