Volantic Systems
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Specimen 05 of 09

mcp-debugger

AI agents can write code. Until they can debug it, they cannot fix it. This fork closes that gap for the .NET ecosystem, including the legacy .NET Framework codebases that pay a lot of bills.

Overview

The upstream project is an MCP server that exposes Debug Adapter Protocol operations as structured tool calls, so an AI agent can step through code, set breakpoints, inspect variables, and walk the stack the same way a developer does in VSCode. Out of the box it covers Python, JavaScript/Node, Rust, and Go.

It did not cover .NET. That is a strange gap, because .NET is where a lot of the production code that needs debugging actually lives, particularly in the kind of long-running enterprise estates AI agents are starting to be pointed at. So I added it. The .NET adapter ships in this fork and pairs with a netcoredbg fork (same org) that I extended to debug legacy .NET Framework runtimes, not just modern CoreCLR. Together they give an AI agent the same step-through capability on a 20-year-old .NET Framework service as it gets on a fresh Python script. Six commits in this repo, four in the netcoredbg one, all original.

Technical

Six commits ahead of upstream as of writing, all on the .NET integration:

  • feat: add .NET/C# debug adapter using netcoredbg: the new adapter, implementing the project’s adapter pattern interface and bridging mcp-debugger’s tool-call surface to netcoredbg’s DAP implementation.
  • fix: add DotnetAdapterPolicy to proxy worker selectAdapterPolicy chain: wiring the adapter into the worker process selection logic so .NET sessions get routed correctly.
  • test: add comprehensive DotnetAdapterPolicy test coverage: unit coverage for the policy logic.
  • fix: ensure attached processes survive debugger shutdown: when the AI agent disconnects, the program under test should not die with the debugger. This was a real bug for attach scenarios.
  • feat: .NET adapter improvements, process utils, and test coverage: process management helpers and broader test coverage.
  • test: add disconnect/detach safety tests and fix stale test expectations: regression tests around disconnect behaviour.

The work sits on top of mcp-debugger’s existing structure: TypeScript, npm-published bundles via tsup (@debugmcp/mcp-debugger), Docker images, STDIO and SSE transport modes, structured JSON tool responses sized for AI consumption. The integration story is straightforward but the surface area is not, because each of these pieces (DAP, MCP, the adapter pattern, the proxy worker, the test harness) has its own conventions you have to respect.

Why You Should Care

Most of the interesting integration work in 2026 lives at the boundary of AI tooling and traditional developer tooling. Model Context Protocol is two years old. Debug Adapter Protocol is a decade old. Bridging them with the right semantics on both sides is the kind of work that determines whether AI agents can be trusted with actual codebases or whether they stay stuck on toy examples.

The way to add a new language to mcp-debugger is to implement its adapter interface. The wrong way is to special-case .NET inside the core. These patches do the right way, with the test coverage that follows: unit coverage for the adapter policy, integration tests for the proxy worker chain, regression tests around disconnect and detach behaviour. The disconnect/detach safety fix is the part you only write if you have actually used attach-mode debuggers in anger. Get it wrong and the process under test dies when the agent disconnects, which is the kind of footgun that does not show up until production.

Together with the netcoredbg fork, this is end-to-end systems work across two ecosystems: from CLR runtime internals up through the MCP tool surface AI agents call. Different languages, different abstraction layers, one capability that did not exist before.

Status

Active fork. Six commits ahead of debugmcp/mcp-debugger. .NET adapter ships from this fork. Pairs with the netcoredbg fork below.

Repo: https://github.com/VolanticSystems/mcp-debugger Upstream: https://github.com/debugmcp/mcp-debugger

mcp-debugger