ASP.NET Core Debugger — MCP Server for AI Agents

ASP.NET Core Debugging MCP Server

The cross-platform .NET debugging MCP — runs on Linux, macOS, and Windows.

An MIT-licensed [MCP](https://modelcontextprotocol.io/) server that lets an AI agent (Claude, etc.) debug your .NET / ASP.NET Core app — netcoredbg bundled for every platform, nothing extra to install.

Instead of *"I think the bug is around line 42, try this"*, the agent runs your code, pauses it, reads the actual runtime values, mutates state to test a fix, and answers grounded in what it actually saw.

Contents

• See it in action — 5 conversations showing the agent at work
• How it works — architecture diagram
• Use it in 3 steps — install + register with Claude
• Platforms — supported OS / architecture matrix
• Tools (27) — full tool surface grouped by purpose
• How this compares — vs. other .NET / DAP MCPs
• Docs — install, examples, tool reference, limits
• License

See it in action

Why is my EF Core query returning empty?

You

GET /users/active returns [], but I know there are active users in the DB. What's the

query actually doing?

Claude

I'll pause inside UserRepository.GetActiveAsync and read what EF Core actually sent.

`sql

SELECT u.*

FROM Users AS u

WHERE u.IsActive = 1 AND u.TenantId = @__tenantId_0

@__tenantId_0 = 0

`

The SQL is correct; the parameter is wrong. TenantId = 0, but your tenants start at 1.

ICurrentUser.TenantId is being read in the repository constructor — before the request

scope resolves it. Fix: read the tenant inside the query (or apply it via HasQueryFilter

with IHttpContextAccessor) instead of capturing it at construction.

Why is my JWT auth returning 401?

You

/admin/users is 401-ing for Anna, but her token looks valid to me. What does the auth

handler actually see?

Claude

I'll break inside JwtBearerHandler.HandleAuthenticateAsync after her request lands.

`

Token signature: ✓ valid

Claims built:

name : anna

role : User

iss : https://auth.staging.example

aud : app-api

exp : 2026-05-26T14:12:00Z (not expired)

`

The token validates fine — but the claim is role=User. Your endpoint is

[Authorize(Roles="Admin")]. So the 401 is correct: Anna isn't actually an admin yet

upstream. Either her IdP record needs updating, or this policy is wrong.

Test a fix without restarting

You

I think capping discount at 100 fixes the bug. Test that hypothesis without me touching

the code.

Claude

I'll pause inside ApplyDiscount on the next checkout and mutate discount in place.

`

Paused at PricingService.cs:47

discount = 250 ← bug: two promos stacked

Set discount = 100, resumed.

Result:

subtotal = $400

final = $300

refund-service complaints: 0

`

Capping at 100 unblocks the flow downstream. Hypothesis confirmed — time to make the edit

for real and decide where the cap belongs (ApplyDiscount itself, or upstream in

PromoEngine).

My app is hung — what's actually blocking?

You

/reports hangs forever in staging. Attach and tell me why.

Claude

Attached. Ran hang_analyze.

`

Thread 12 (HTTP request)

→ blockedOnTask at ReportService.cs:38 Task.Wait() on T#14

Thread 14 (worker)

→ blockedOnMonitor at SqlConnectionPool.cs:91

waiting for SqlConnection

(pool max=5, in-use=5)

`

Classic sync-over-async deadlock. Thread 12 calls .Wait() on a task that itself needs to

open another SqlConnection from a fully-held pool. The connection it's holding can't be

released until the task completes; the task can't proceed until a connection frees up. Fix:

await all the way down in ReportService, or don't hold a connection across the awaited

call.

Where is a slow request actually spending its time?

You

GET /order/42 takes 800ms. I don't want to set breakpoints all over — just show me where

the time is going.

Claude

I'll auto-instrument your order pipeline and fire the request. Each entry logs the

timestamp + arguments, then resumes — the code runs near-normal speed.

`

[+ 4ms] → OrderController.GetOrder() id=42

[+ 6ms] --→ OrderService.LookupOrder() id=42

[+ 9ms] ----→ OrderRepository.FetchById() id=42

[+ 14ms] ------→ SqlClient.ExecuteQuery() sql="SELECT * FROM orders WHERE id=42"

[+ 287ms] ----→ EnrichmentService.Enrich() raw="rows(...)"

[+ 781ms] ------→ HttpClient.PostAsync() url="https://crm.internal/enrich"

`

Time is in the CRM enrichment HTTP call — 500ms inside HttpClient.PostAsync. DB itself

was 5ms. Worth caching EnrichmentService.Enrich or moving it off the request path.

More examples →

How it works

Claude (MCP client)

│ MCP (stdio / JSON-RPC) ▼ aspnetcore-debugger-mcp ← this server │ DAP (Debug Adapter Protocol) ▼ netcoredbg ← Samsung's MIT-licensed .NET debugger, child process │ ICorDebug ▼ target .NET process

A protocol bridge with agent-friendly composites on top — exception_autopsy, stack_explore, hang_analyze, and the trace tools — that bundle multiple DAP requests into a single tool call.

Use it in 3 steps

1. Install the tool — needs the .NET 10 SDK.

   dotnet tool install -g AspNetCoreDebuggerMcp --prerelease

The package bundles prebuilt netcoredbg for linux-x64, linux-arm64, win-x64, osx-x64, and osx-arm64 — no separate install needed.

1. Register with Claude — either the quick CLI command:

   claude mcp add aspnetcore-debugger -- aspnetcore-debugger-mcp

…or edit .mcp.json (project-scoped) / ~/.claude.json (global) / claude_desktop_config.json (Claude Desktop) directly:

   {

"mcpServers": { "aspnetcore-debugger": { "command": "aspnetcore-debugger-mcp" } } }

3. **Just chat with Claude.** `/mcp` confirms it's connected. From there, describe what you want — *"why does this endpoint return null"* — and the agent picks the right tools.

Full install + troubleshooting →

Platforms

Bundled netcoredbg binary is selected at runtime — no per-platform install dance.

Requires the .NET 10 SDK on the host. The MCP server itself is a cross-platform .NET global tool — same install command everywhere.

Tools (27)

Full tool reference with parameters →

How this compares

Different sweet spots: this project is the MIT, cross-platform option, with ASP.NET-flavoured composites on top of a DAP. debug-mcp goes deeper into runtime internals via ICorDebug but is Linux-only and AGPL today.

Docs

• [Install & configure](docs/install.md) — 3 steps, both Claude Code & Desktop, troubleshooting
• [What you can do with it](docs/examples.md) — 7 things you can ask Claude to do for you
• [Full tool reference](docs/tools.md) — every parameter on every tool
• [Known limits](docs/limits.md) — when *not* to use this tool, adapter & tracing limits
• [macOS Apple Silicon — building netcoredbg](docs/macos-arm64.md)
• [Contributing](docs/contributing.md) — repo layout, tests, dev loop

License

MIT — see LICENSE. Built on netcoredbg (MIT) and the ModelContextProtocol SDK (MIT).