LatencyPlugin

Delays responses by a random number of milliseconds from the configured range. Supports both HTTP requests and STDIO communication.

Configuration example

{
  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v2.0.0/rc.schema.json",
  "plugins": [
    {
      "name": "LatencyPlugin",
      "enabled": true,
      "pluginPath": "~appFolder/plugins/DevProxy.Plugins.dll",
      "configSection": "latencyPlugin"
    }
  ],
  "latencyPlugin": {
    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v2.0.0/latencyplugin.schema.json",
    "minMs": 200,
    "maxMs": 10000
  }
}

Configuration properties

Property	Description	Default
minMs	The minimum amount of delay added to a request in milliseconds.	0
maxMs	The maximum amount of delay added to a request in milliseconds.	5000

Command line options

None

STDIO support

When you use the LatencyPlugin with the STDIO command, the plugin adds artificial latency to stdout responses. Simulating latency is useful for testing how your application handles slow Model Context Protocol (MCP) server responses or other STDIO-based tools.

Configuration example for STDIO

{
  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v2.1.0/rc.schema.json",
  "plugins": [
    {
      "name": "LatencyPlugin",
      "enabled": true,
      "pluginPath": "~appFolder/plugins/DevProxy.Plugins.dll",
      "configSection": "latencyPlugin"
    },
    {
      "name": "MockSTDIOResponsePlugin",
      "enabled": true,
      "pluginPath": "~appFolder/plugins/DevProxy.Plugins.dll",
      "configSection": "mockSTDIOResponsePlugin"
    }
  ],
  "latencyPlugin": {
    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v2.1.0/latencyplugin.schema.json",
    "minMs": 100,
    "maxMs": 500
  },
  "mockSTDIOResponsePlugin": {
    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v2.1.0/mockSTDIOresponseplugin.schema.json",
    "mocksFile": "STDIO-mocks.json"
  }
}

Then run:

devproxy STDIO npx -y @modelcontextprotocol/server-filesystem

Next step

Simulate slow API responses