jmeter-mcp-server

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update_thread_group

Modify JMeter thread group parameters in a .jmx file—set thread count, ramp-up, loops, duration, and scheduler—to customize load test execution.

Instructions

Update thread group settings (threads, ramp-up, loops, duration)

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": {
      "testfile": "<testfile>"
    },
    "name": "update_thread_group"
  }
}

Input Schema

Name	Required	Description
`delay`	No	Startup delay in seconds
`loops`	No	Loop count (-1 for infinite)
`duration`	No	Test duration in seconds
`rampTime`	No	Ramp-up time in seconds
`testfile`	Yes	Path to the .jmx file
`scheduler`	No	Enable/disable scheduler
`numThreads`	No	Number of threads (virtual users)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Aug 30, 2026

TDQS

B3.2/5.0

Behavior2/5

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

With no annotations, the description carries the full burden of explaining behavior. It only says 'update' but does not disclose whether partial updates are supported, whether unspecified settings are reset or preserved, what side effects occur, or what the response looks like. This is a significant gap for a mutation tool.

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?

The description is a single, efficient sentence that front-loads the action and resource and lists the most relevant settings. There is no wasted wording or redundant repetition.

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

Completeness2/5

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

For a tool with 7 parameters, no annotations, and no output schema, this description is too thin. It does not explain the required testfile parameter, partial-update semantics, scheduler behavior, or call outcome. An agent would still need to infer important operational details.

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 the schema already documents each parameter. The description names a few settings (threads, ramp-up, loops, duration) but adds no new meaning beyond the schema; it also omits delay, scheduler, and testfile from its list.

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?

The description clearly states the action ('update') and resource ('thread group settings') and lists the key configurable fields. It is distinct from sibling tools like create_test_plan or add_http_sampler, though it does not explicitly differentiate itself from all potential update-like tools.

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

Usage Guidelines3/5

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

The description implies use for modifying an existing thread group's load profile, but it does not specify when to use this tool versus alternatives, nor does it mention prerequisites such as an existing test plan or that the testfile must reference a valid .jmx file.

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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