Config Files

Store your load test configuration in a YAML file so it can be version-controlled alongside your code.

Why use a config file?

• Reproducible runs — same config, same test every time
• Version control — track changes to your performance requirements
• CI integration — check in lmn.yaml next to your service and run it on every PR

Basic structure

run:
  host: https://api.example.com
  method: post
  headers:
    Authorization: "Bearer ${API_TOKEN}"
    Content-Type: application/json

execution:
  request_count: 1000
  concurrency: 50

thresholds:
  - metric: latency_p99
    operator: lt
    value: 500.0
  - metric: error_rate
    operator: lt
    value: 0.01

Run it:

lmn run -f lmn.yaml

CLI flags override config

Any flag passed on the command line takes precedence over the config file. This lets you use a base config and override specific values:

# Override host for local testing
lmn run -f lmn.yaml -H http://localhost:8080

Using a template

Point to a request body template file:

run:
  host: https://api.example.com
  method: post
  request_template: ./templates/order.json

Or use a saved alias (see Template Aliases):

run:
  host: https://api.example.com
  method: post
  alias: my-order

Curve mode

Replace request_count/concurrency with stages for time-based execution:

execution:
  stages:
    - duration: 30s
      target_vus: 10
    - duration: 2m
      target_vus: 50
      ramp: linear
    - duration: 30s
      target_vus: 0
      ramp: linear

Scenarios

Define multi-step user flows instead of a single endpoint. When scenarios is present, run.host and run.method are not used — each step defines its own target.

run:
  headers:
    Authorization: "Bearer ${API_TOKEN}"    # global headers apply to all steps

scenarios:
  - name: checkout
    weight: 3                               # 75% of VUs run this scenario
    on_step_failure: abort_iteration        # skip remaining steps on failure
    steps:
      - name: login
        host: https://api.example.com/auth
        method: post
      - name: pay
        host: https://api.example.com/checkout
        method: post
  - name: browse
    weight: 1                               # 25% of VUs
    steps:
      - name: list
        host: https://api.example.com/products

execution:
  request_count: 1000                       # 1000 scenario iterations (not requests)
  concurrency: 20

Headers merge in three layers: global (run.headers + CLI) → scenario → step, with case-insensitive last-wins. Each step can also have its own request_template and response_template.

Scenarios work with both fixed and curve modes. See Config File Reference for the full schema.

Full reference

See Config File Reference for every field, type, default, and constraint.