LatencyPlugin

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

Configuration example

{
  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/rc.schema.json",
  "plugins": [
    {
      "name": "LatencyPlugin",
      "enabled": true,
      "pluginPath": "~appFolder/plugins/DevProxy.Plugins.dll",
      "configSection": "latencyPlugin"
    }
  ],
  "latencyPlugin": {
    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/latencyplugin.schema.json",
    "minMs": 200,
    "maxMs": 10000
  }
}

Configuration properties

Command line options

None

Remarks

Dev Proxy validates the plugin's configuration when it starts. If minMs is greater than maxMs, Dev Proxy doesn't start and shows an error, for example:

LatencyPlugin: minMs (500) must be less than or equal to maxMs (100).

To add a fixed delay, set minMs and maxMs to the same value.

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

{
  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/rc.schema.json",
  "plugins": [
    {
      "name": "LatencyPlugin",
      "enabled": true,
      "pluginPath": "~appFolder/plugins/DevProxy.Plugins.dll",
      "configSection": "latencyPlugin"
    },
    {
      "name": "MockStdioResponsePlugin",
      "enabled": true,
      "pluginPath": "~appFolder/plugins/DevProxy.Plugins.dll",
      "configSection": "mockStdioResponsePlugin"
    }
  ],
  "latencyPlugin": {
    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/latencyplugin.schema.json",
    "minMs": 100,
    "maxMs": 500
  },
  "mockStdioResponsePlugin": {
    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/mockstdioresponseplugin.schema.json",
    "mocksFile": "stdio-mocks.json"
  }
}

Then run:

devproxy stdio npx -y @modelcontextprotocol/server-filesystem

Next step