fnx — SKU-aware Azure Functions Local Emulator

Run Azure Functions locally with the exact host version your target SKU uses in production. No more "works locally, breaks in Azure."

Install

npm install -g @vrdmr/fnx-test

Or run without installing:

npx @vrdmr/fnx-test start --sku flex --app-path ./my-app

Quick Start

# List available SKUs
fnx start --sku list

# Run your function app with the Flex Consumption host
fnx start --sku flex --app-path ./my-function-app

# Run with Windows Consumption host
fnx start --sku windows-consumption --app-path ./my-function-app

What It Does

fnx downloads and caches the self-contained host binary for your target SKU, then launches your function app against it. Each SKU maps to a specific host version, extension bundle version, and runtime configuration — matching what runs in Azure.

fnx start --sku flex
  ├── Resolves SKU profile (host v4.1047.100, bundle v4.30.0)
  ├── Downloads host binary (cached at ~/.fnx/hosts/)
  ├── Downloads extension bundle (cached at ~/.fnx/bundles/)
  ├── Auto-starts Azurite if needed (storage triggers)
  └── Launches host → your functions are live

Available SKUs

| SKU | Description | |-----|-------------| | flex | Flex Consumption (latest host, latest bundle) | | linux-premium | Linux Premium (EP1/EP2/EP3) | | linux-consumption | Linux Consumption | | windows-consumption | Windows Consumption | | windows-dedicated | Windows Dedicated (App Service Plan) |

Commands

fnx start --sku <sku> --app-path <path>   # Run function app
fnx start --sku list                         # List available SKUs
fnx warmup [--sku <sku>] [--all]            # Pre-download host + bundle
fnx sync [host|extensions] [--sku <sku>]    # Reconcile cache with latest catalog / rollback
fnx templates-mcp                            # Start MCP server for AI agents
fnx pack --app-path <path>                # Package function app as deployment zip

Upgrades, Rollbacks, and Cache Retention

• On fnx start, fnx warmup, and fnx sync, fnx attempts to refresh the SKU catalog from CDN first.
• If catalog host version is newer than your local cache, fnx highlights that and recommends fnx sync (or fnx sync host).
• If catalog host version is lower than a locally cached version (service rollback), fnx warns and recommends syncing back to the supported host.
• fnx sync defaults to keeping only the latest 2 host and bundle versions to avoid cache bloat (--keep <n> to override).
• fnx also checks npm for newer fnx CLI releases and prints an upgrade tip when available.
• Version comparisons use numeric dot-segment precedence (e.g. 4.1047.100 > 4.1046.999) with support for v prefixes and pre-release suffixes.

MCP Server (for AI Agents)

fnx includes an MCP server that exposes Azure Functions templates to AI coding assistants:

// .vscode/mcp.json
{
  "servers": {
    "azure-functions-templates": {
      "type": "stdio",
      "command": "npx",
      "args": ["@vrdmr/fnx-test", "templates-mcp"]
    }
  }
}

Or use the direct entrypoint for faster cold starts:

{
  "servers": {
    "azure-functions-templates": {
      "type": "stdio",
      "command": "npx",
      "args": ["fnx-template-mcp"]
    }
  }
}

Features

• SKU-aware — match the exact host version your target Azure environment runs
• Zero dependencies — pure Node.js 18+, no native modules
• Offline-capable — bundled profiles + cached hosts work without network
• Auto Azurite — storage emulator starts automatically for blob/queue/timer triggers
• .NET isolated only — blocks in-process .NET projects with migration guidance
• MCP integration — AI agents can discover templates and SKU profiles

Requirements

• Node.js 18+
• ~200MB disk per host version (cached at ~/.fnx/)

License

MIT