feat: add Dev Proxy v2.1.0 release notes with configuration hot reload and stdio proxying features

Author: waldekmastykarz

public/blog/images/og-image-dev-proxy-v2-1-with-configuration-hot-reload-and-stdio-proxying.webp

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+---
+title: "Dev Proxy v2.1 with configuration hot reload and stdio proxying"
+description: "We're excited to announce the release of Dev Proxy v2.1.0! This release brings two major productivity features that developers have been asking for: automatic configuration hot reload and stdio traffic proxying."
+date: 2026-01-29
+author: "Waldek Mastykarz, Garry Trinder"
+tags: ["release"]
+image: "/blog/images/og-image-dev-proxy-v2-1-with-configuration-hot-reload-and-stdio-proxying.webp"
+---
+
+We're excited to announce the release of Dev Proxy v2.1.0! This release brings two major productivity features that developers have been asking for: automatic configuration hot reload and stdio traffic proxying – perfect for testing MCP servers and other stdio-based tools. In this version:
+
+- **Configuration hot reload** – Dev Proxy automatically restarts when you change the config file
+- **Stdio traffic proxying** – Intercept, inspect, and mock stdin/stdout/stderr traffic
+- **New `--api-port` command-line option**
+- **LatencyPlugin** now supports delays greater than 10 seconds
+- **CORS support** for the Dev Proxy web API
+- Multiple bug fixes and improvements
+
+## Configuration hot reload
+
+No more manual restarts when tweaking your proxy configuration. Dev Proxy now watches your configuration file and automatically restarts when you save changes.
+
+This was one of our oldest feature requests – dating back to April 2023. Whether you're adjusting failure rates, adding plugins, or changing URL patterns, your changes take effect immediately. Just save the file and keep working.
+
+### Why this matters
+
+When you're iterating on your proxy configuration – fine-tuning error rates, adjusting mock responses, or testing different plugin combinations – stopping and restarting the proxy breaks your flow. With hot reload, your development loop gets tighter and more productive.
+
+## Stdio traffic proxying
+
+Modern AI development increasingly relies on tools that communicate via stdin/stdout/stderr – particularly MCP (Model Context Protocol) servers. Now you can intercept and manipulate this traffic just like you do with HTTP.
+
+### How it works
+
+Wrap any executable with Dev Proxy: `devproxy stdio npx my-mcp-server`
+
+Dev Proxy proxies all stdin, stdout, and stderr traffic, letting you:
+
+- **Inspect messages** in Chrome DevTools Network tab (appear as `stdio://` URLs)
+- **Mock responses** using the new MockStdioResponsePlugin
+- **Simulate latency** with the existing LatencyPlugin
+- **Use placeholders** like `@stdin.body.id` in your mock responses
+
+This opens up Dev Proxy to an entirely new category of applications – anywhere you need to test, debug, or mock stdio-based communication.
+
+## New `--api-port` command-line option
+
+Running multiple Dev Proxy instances? Need the default port 8897 for something else? You can now configure the API port directly from the command line: `devproxy --api-port 9000`
+
+No need to create a separate config file just to change the port.
+
+## LatencyPlugin improvements
+
+Previously, the LatencyPlugin schema artificially limited `maxMs` to 10,000 milliseconds (10 seconds). This restriction never existed in the actual code – it was just a schema limitation.
+
+### What changed
+
+The schema now allows any value for `maxMs`, letting you simulate delays of any duration – useful for testing timeout handling and slow network conditions.
+
+## CORS support for Dev Proxy web API
+
+Building browser-based developer tools that interact with Dev Proxy? The API on port 8897 now supports cross-origin requests, so your web applications can call endpoints like `/proxy/jwtToken` without CORS errors.
+
+## Bug fixes
+
+- **`-e` flag now works correctly** – Starting Dev Proxy with environment variable presets no longer throws a `FormatException`
+- **AuthPlugin ApiKey validation fixed** – The plugin no longer incorrectly reports missing `ApiKey.Parameters` when they're properly configured
+- **GenericRandomErrorPlugin method matching** – Error responses without a specified HTTP method now correctly match all methods (GET, POST, PUT, DELETE, etc.) instead of only GET
+- **MockResponsePlugin Content-Type handling** – No more spurious JSON parsing warnings when using form data or other non-JSON content types
+- **CRUD API data file hot reload** – Data file changes now take effect immediately without restarting Dev Proxy
+
+## Dev Proxy Toolkit 1.12.0
+
+[Dev Proxy Toolkit](https://marketplace.visualstudio.com/items?itemName=garrytrinder.dev-proxy-toolkit) is an extension that makes it easier to work with Dev Proxy from within Visual Studio Code. This release focuses on configuration validation and developer experience improvements:
+
+- **Custom installation paths** — New `devProxyPath` setting for non-standard Dev Proxy locations
+- **Smarter config validation** — Config section properties are now validated against the Dev Proxy schema, catching invalid values, unknown properties, and schema version mismatches
+- **Enhanced diagnostics** — More precise highlighting, unique diagnostic codes with documentation links, and new warnings for empty `urlsToWatch` and optional plugin configurations
+- **More quick fixes** — Add optional or missing plugin config sections, update schema versions across files, and remove unknown properties
+- **Better plugin support** — `AuthPlugin` and `LanguageModelFailurePlugin` fixes, plus new snippets for `GraphConnectorGuidancePlugin` and `MockStdioResponsePlugin`
+
+Checkout out the [changelog](https://marketplace.visualstudio.com/items/garrytrinder.dev-proxy-toolkit/changelog) for more information on changes and bug fixes.
+
+## Why upgrade to v2.1.0?
+
+- **Faster iteration** – Configuration hot reload means no more manual restarts
+- **MCP server testing** – Inspect, mock, and debug stdio traffic with familiar workflows
+- **More flexibility** – Runtime port configuration and unlimited latency simulation
+- **Cleaner experience** – Multiple bug fixes reduce friction and noise
+
+## Try it now
+
+Download **Dev Proxy v2.1.0** today and build better API-connected applications with confidence!
+
+Thanks to [Nitesh Singhal](https://github.com/niteshsinghal85) for contributing to this release.
+
+Got feedback or ideas? [Join us](https://github.com/dotnet/dev-proxy/discussions) and be part of the conversation.