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jmeter-mcp-server

by juliodelimas
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add_thread_group

Add a thread group to a JMeter test plan to define concurrent virtual users and set ramp-up time for load testing.

Instructions

Add a Thread Group (virtual users) under the given parent node (usually the TestPlan root).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
nameYes
loopsNoNumber of loop iterations per thread, -1 for infinite
planIdYes
parentIdYesId of the node to attach this thread group under
numThreadsYesNumber of concurrent virtual users
delaySecondsNoStartup delay: seconds to wait before this thread group starts (enables the scheduler). Use it to stage thread groups, e.g. a second group that begins 5s after the first.
durationSecondsNoIf set, run on a scheduler for this many seconds instead of a fixed loop count
rampTimeSecondsYesSeconds to reach full thread count

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.4.5
    • addedInput schema / properties / delaySeconds
      Added value: +{
+  "description": "Startup delay: seconds to wait before this thread group starts (enables the scheduler). Use it to stage thread groups, e.g. a second group that begins 5s after the first.",
+  "exclusiveMinimum": 0,
+  "type": "number"
+}
  2. First observedv0.1.2

TDQS

C2.9/5.0
Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. The verb 'Add' implies a mutation, but the description does not state side effects, whether the operation is reversible, required permissions, or what the return value looks like. It adds no behavioral context beyond the obvious action.

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?

The description is a single, front-loaded sentence with no wasted words. It efficiently conveys the core purpose and a key detail about the parent node. However, it is so terse that it lacks depth, but conciseness is a strength here.

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 8 parameters and no output schema, this description is inadequate. It does not explain the role of a Thread Group in a test plan, typical usage patterns, or how this tool relates to its setup/teardown siblings. The agent is left to infer too much, relying solely on the schema for semantics.

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 75%, so most parameters are already documented. The description itself adds no parameter meaning beyond what the schema provides, e.g., it does not elaborate on how numThreads or rampTimeSeconds interact. Given the moderate coverage, a baseline of 3 is appropriate.

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 ('Add a Thread Group') and the resource ('virtual users') and specifies the attachment point ('under the given parent node'). However, it does not distinguish this from the sibling tools add_setup_thread_group and add_teardown_thread_group, so an agent might not know which one to pick without further investigation.

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 provides no guidance on when to use this tool versus alternatives. It only hints that the parent node is usually the TestPlan root, which is context about the parameter, not about selection criteria. No exclusions or alternative suggestions are given.

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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