What is roslyn-mcp-decompile?

Assembly-resolution and decompilation rules for .NET projects. They describe how to find the exact DLL, or compiled library, using project dependency files, the NuGet cache, or the .NET runtime before opening it with ILSpy.

Use them when inspecting C# assemblies, resolving project or package references, checking Azure DevOps or other .NET APIs, or working on assembly-resolution tests.

They reduce the risk of analysing the wrong library or inventing an API that is not present. They also set a safer path for handling large types and testing the resolver.

roslyn-mcp-decompile — Cursor rule for Cursor by VuDZ/RoslynMcpServer

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Clone the repo

git clone --depth 1 https://github.com/VuDZ/RoslynMcpServer

Made for: Cursor.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/rules/vudz/roslynmcpserver/roslyn-mcp-decompile/github.svg)](https://agentmods.dev/rules/vudz/roslynmcpserver/roslyn-mcp-decompile)

Your own site

<a href="https://agentmods.dev/rules/vudz/roslynmcpserver/roslyn-mcp-decompile"><img src="https://agentmods.dev/badge/rules/vudz/roslynmcpserver/roslyn-mcp-decompile/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/rules/vudz/roslynmcpserver/roslyn-mcp-decompile"><img src="https://agentmods.dev/badge/rules/vudz/roslynmcpserver/roslyn-mcp-decompile.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 0 Nothing until a file matches its globs; then the whole rule loads.

When invoked 287 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00000	$0.00287
Opus 5	$0.00000	$0.00143
Sonnet 5	$0.00000	$0.00057
Haiku 4.5	$0.00000	$0.00029

Measured 2d ago against content hash 8fabcd9816f5, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-16, from the pricing page.

Security

Grade A, and why

roslyn-mcp-decompile scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/rules/roslyn-mcp-decompile.mdc · 31 lines

What it actually says

Decompile & assembly resolve

Exact resolve (v1.0.13+)

AssemblyReferenceResolver / DepsJsonAssemblyPathResolver / NuGetFallbackAssemblyResolver:

Prefer exact {assemblyName}.dll — no fuzzy Contains matching (wrong DLL / BadImage).
Resolve via project deps.json, then NuGet cache, then BCL / runtime pack maps (BclAssemblyPackageMap).
Tools accept assemblyName (after load_workspace) or assemblyPath.

DecompilerHost

ILSpy-backed; circuit breakers (e.g. decompile_type max ~500 lines). Large types → skeleton first.

API assumptions

Do not invent NuGet APIs from memory — decompile first. Especially Azure DevOps / TFS:

Decompile Microsoft.VisualStudio.Services.WebApi (or graph-named assembly).
Do not assume cloud VssConnection.CreateAsync(organization) for on-prem — collection URI + Windows/PAT.

Tests

AssemblyReferenceResolverTests, DepsJsonAssemblyPathResolverTests, NuGetFallbackAssemblyResolverTests.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago First seen · 31 lines · 0 tokens per session scan A 8fabcd9816f5

Subscribe to this mod's changes

roslyn-mcp-decompile is a cursor rule published in the GitHub repository VuDZ/RoslynMcpServer (7 stars, last pushed yesterday), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 287 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-14.

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