Subtrace tracks all requests by default, but you can exclude certain requests with a simple YAML-based config file. Here’s an example: 
rules:
  - if: response.status >= 400
    then: include
  - if: request.url == "/health"
    then: exclude
  - if: request.method == "HEAD"
    then: exclude
To use a config file, set the --config command line flag when starting Subtrace: 
subtrace run --config=/path/to/subtrace.yaml -- node app.js
You can also pass this as an environment variable: 
export SUBTRACE_CONFIG=/path/to/subtrace.yaml
At request time, Subtrace will evaluate all rules in order until a matching rule is found. Using the first matching rule’s then field, Subtrace decides whether the request should be included or excluded. If no matching rule is found, the request is included by default.

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Syntax

The if condition is written using CEL, a simple language with a syntax similar to JavaScript. Here’s a list of commonly used syntax as reference examples:
  • request.method == "POST"
  • request.url != "/robots.txt"
  • request.url.contains("dashboard")
  • request.url.startsWith("/api/")
  • request.url.endsWith(".jpg") || request.url.endsWith(".png")
  • response.status >= 400 && response.status <= 499
You can find the complete CEL language definition here.