Allows decompiling .NET assemblies into C# source code, listing types, decompiling specific types or entire assemblies, and searching across decompiled code using ILSpy.
Click on "Install Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type @ followed by the MCP server name and your instructions, e.g., "@mcp-dotnet list types in MyAssembly.dll"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
Русская версия ниже / Russian version below
A small Model Context Protocol (MCP) server that lets an LLM read .NET
assemblies as C#. It is a thin wrapper around the official ILSpy CLI
(ilspycmd), exposed over stdio so any MCP-capable client can list types,
decompile a single class, decompile the whole assembly into a project tree,
or grep across the decompiled source.
LLMs are good at reading source code, not raw IL bytecode. ILSpy already
turns CIL into faithful C#, but invoking it from a chat agent is awkward —
you end up shelling out to ilspycmd by hand and pasting the output back
into the conversation. This server formalizes that loop:
list-types first, so the model knows which type to look at without
dumping a megabyte of decompilation into context.
decompile-type for targeted reads — one fully-qualified class at a time.
decompile-assembly when the model genuinely wants the whole project
tree, e.g. before running a project-wide grep.
search-source decompiles once, caches the output, and greps across all
the resulting .cs files. Subsequent searches reuse the cached tree.
The target assembly is never executed. Everything is static.
It also handles the common modern case of .NET 6/7/8 single-file
deployments — point path at the published .exe and ILSpy 10+ resolves
the embedded core assembly automatically.
Related MCP server: dotnet-sherlock-mcp
Tool | What it does |
| List declared types in an assembly. Optional |
| Decompile one fully-qualified type to C#. Optional IL appended via |
| Decompile to a folder of |
| Decompile (once, cached) and grep the C# tree for a regex; returns file/line/snippet. |
# 1. ILSpy CLI (one-time, requires .NET SDK 6+)
dotnet tool install --global ilspycmd
# 2. This server
git clone https://github.com/beekamai/mcp-dotnet.git
cd mcp-dotnet
npm install
npm run buildIf ilspycmd is not on PATH, set the ILSPYCMD environment variable to its
absolute path. The server also auto-detects the default
%USERPROFILE%\.dotnet\tools\ilspycmd.exe location on Windows and
~/.dotnet/tools/ilspycmd on POSIX.
Wire it into any MCP-capable client over stdio:
your-mcp-client mcp add dotnet --scope user -- node /absolute/path/to/mcp-dotnet/dist/index.jsAll tools take absolute paths. Working directory differences between the MCP client and this server are common, so the server refuses to guess.
decompile-assembly and the first search-source on a fresh assembly can
take tens of seconds to several minutes depending on size — the timeout is
10 minutes.
search-source caches the decompiled tree under
<assemblyDir>/.mcp-dotnet-<assemblyName>/ by default. Pass an explicit
outDir to control placement, or delete the cache to force re-decompilation.
The server runs ilspycmd as a child process and never exposes its stdin.
No code from the target assembly is executed at any point.
MIT.
Небольшой MCP-сервер, который даёт языковой модели возможность читать
.NET-сборки как C#-исходники. Это тонкая обёртка над официальной
консольной утилитой ILSpy (ilspycmd) поверх stdio: модель может получить
список типов, декомпилировать один класс, развернуть всю сборку в дерево
.cs-файлов или прогнать regex по исходнику.
LLM хорошо читают исходный код и плохо — IL. ILSpy и так умеет превращать
CIL в адекватный C#, но дёргать ilspycmd руками из чата неудобно — каждый
раз shell-out и копипаст в контекст. Этот сервер формализует цикл:
Сначала list-types, чтобы модель не тащила мегабайты декомпила в
контекст ради того, чтобы выяснить какой класс ей нужен.
decompile-type — точечно один полностью-квалифицированный тип.
decompile-assembly — когда нужен весь проектный tree (например, чтобы
потом сделать project-wide grep).
search-source — декомпилирует один раз, кэширует результат и ищет regex
по всем .cs. Повторные поиски используют кэш.
Целевую сборку никто не запускает. Всё статично.
Сервер также корректно работает с single-file deployment .NET 6/7/8 —
указываешь path на опубликованный .exe, ILSpy 10+ сам находит
встроенный основной assembly.
Тул | Что делает |
| Список типов сборки. Опциональный фильтр |
| Декомпиляция одного типа в C#. С опциональным IL через |
| Развёртывает сборку в папку |
| Один раз декомпилирует (с кэшем), потом regex-grep по |
# 1. ILSpy CLI (один раз, нужен .NET SDK 6+)
dotnet tool install --global ilspycmd
# 2. Сам сервер
git clone https://github.com/beekamai/mcp-dotnet.git
cd mcp-dotnet
npm install
npm run buildЕсли ilspycmd не попал в PATH — выставь переменную окружения ILSPYCMD
с абсолютным путём. Сервер также автоматически находит дефолтные пути:
%USERPROFILE%\.dotnet\tools\ilspycmd.exe на Windows и
~/.dotnet/tools/ilspycmd на POSIX.
Подключение к MCP-клиенту через stdio:
your-mcp-client mcp add dotnet --scope user -- node /абсолютный/путь/к/mcp-dotnet/dist/index.jsВсе тулы принимают абсолютные пути. Рабочая директория MCP-клиента и сервера часто различаются, поэтому сервер ничего не угадывает.
decompile-assembly и первый search-source на свежей сборке могут
занимать от десятков секунд до нескольких минут — таймаут 10 минут.
search-source кэширует декомпилированное дерево в
<dir-сборки>/.mcp-dotnet-<имя-сборки>/. Если хочется в другое место —
передай outDir явно. Удаление каталога заставит декомпилировать заново.
ilspycmd запускается дочерним процессом, его stdin не пробрасывается.
Код целевой сборки нигде не исполняется.
MIT.
Decompile the entire assembly into a folder of .cs files (a compilable project). Use this when you want to grep across the whole codebase. Returns the output directory and a flat list of generated files. Heavy - prefer list-types + decompile-type for targeted lookups.
| Name | Required | Description | Default |
|---|---|---|---|
| path | Yes | Absolute path to the assembly. | |
| outDir | Yes | Absolute path where the decompiled project tree should be written. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description discloses that the tool is 'Heavy' (resource-intensive) and returns an output directory and flat list of files. It implies writing to disk but does not specify overwrite behavior or permissions needed.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Three sentences, all essential: purpose, use case, return info, and caveat. Front-loaded and concise with no redundancy.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a tool with two simple parameters and no output schema, the description covers the return format ('output directory and flat list of generated files') and hints at the output being a compilable project, making it complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, so baseline is 3. The description does not add meaning beyond the schema's parameter descriptions, which are already clear.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'decompile' and the resource 'entire assembly into .cs files', and differentiates from sibling tools by specifying that it is for grepping across the whole codebase and that alternatives are better for targeted lookups.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly states when to use ('when you want to grep across the whole codebase') and when not ('prefer list-types + decompile-type for targeted lookups'), providing clear guidance for tool selection.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Decompile a single fully-qualified type into C# source. Pass the fully qualified name as printed by list-types (e.g. 'Acme.Bot.LicenseManager').
| Name | Required | Description | Default |
|---|---|---|---|
| path | Yes | Absolute path to the assembly. | |
| type | Yes | Fully-qualified type name to decompile. | |
| languageVersion | No | C# language version. Default: Latest. Useful values: CSharp7_3, CSharp10_0, Latest. | |
| includeIl | No | Append IL alongside the C# (ilspycmd -il). Default: false. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided, so description must carry the full burden. It only states the basic action and parameter format, but omits information about output, errors, permissions, or side effects.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, no redundancy, action-first structure provides maximum information with minimal text.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Adequately describes the tool's core function and input requirements, but lacks details about output format, error handling, and usage context relative to siblings.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema descriptions cover all parameters (100% coverage), and the description adds value by specifying that the type name should come from list-types, which clarifies the expected format beyond the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states 'Decompile a single fully-qualified type into C# source', which is a specific verb-resource combination. Distinguishes from sibling 'decompile-assembly' by targeting a single type rather than a whole assembly.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Provides a hint to use the output of list-types for the type name, but does not explicitly say when to use this tool vs alternatives or when not to use it.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
List declared types in a .NET assembly (classes, interfaces, structs, delegates, enums). Use this first to find candidates before calling decompile-type. Works on .dll, .exe, and .NET 6+ single-file deployments (the embedded core assembly is decompiled directly).
| Name | Required | Description | Default |
|---|---|---|---|
| path | Yes | Absolute path to the assembly. | |
| kinds | No | Comma-separated subset of: c (class), i (interface), s (struct), d (delegate), e (enum). Default: 'c,i,s,d,e'. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Without annotations, the description discloses supported file types and special handling for single-file deployments. It implies read-only operation but does not explicitly state safety or side effects.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, no wasted words. Purpose and usage are front-loaded. Highly concise.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Completely covers the tool's purpose and relationship to sibling. Lacks output format details, but for a list tool with no output schema, this is acceptable.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, so baseline is 3. The description adds mapping from letters to full type names but does not provide significant additional meaning beyond the schema descriptions.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states it lists declared types in a .NET assembly, specifying categories (classes, interfaces, structs, delegates, enums). It distinguishes from sibling 'decompile-type' by advising to use this first.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly says 'Use this first to find candidates before calling decompile-type', providing clear context. Also notes compatibility with .dll, .exe, and .NET 6+ single-file deployments, but does not mention exclusions or alternatives for other siblings.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Decompile the assembly to a temporary directory then grep its C# source for a pattern. Returns the matching files with line snippets. The decompiled tree is preserved on disk for follow-up queries (path returned in 'outDir').
| Name | Required | Description | Default |
|---|---|---|---|
| path | Yes | Absolute path to the assembly. | |
| outDir | No | Optional output directory to reuse; otherwise a temp dir under the assembly's directory is created. | |
| pattern | Yes | JavaScript regex pattern. Case-insensitive flag is implied. | |
| maxMatches | No |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries full burden. It discloses that decompilation writes to a temporary directory, preserves the tree on disk for follow-up, and returns the outDir path. It does not mention safety or permissions, but the main behaviors are transparent.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Three sentences, all informative and front-loaded. The first sentence captures the core action, the second explains output, and the third adds key behavioral detail. No extraneous words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Despite no output schema, the description explains both return values and disk persistence. It covers the necessary context for an agent to invoke the tool correctly, given the sibling tool set.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is high (75%), but the description adds value by explaining the purpose of outDir (optional reuse, returned path) and the pattern's case-insensitive nature. This provides context beyond the schema definitions.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool decompiles an assembly and then greps its C# source for a pattern, distinguishing it from sibling tools like decompile-assembly (decompilation only) and decompile-type (specific type decompilation). It specifies the output (matching files with line snippets) and the preserved disk state.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage for searching decompiled code but does not explicitly compare with siblings or state when not to use. It lacks guidance on alternatives or prerequisites.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Each tool has a clearly distinct purpose: list-types for browsing, decompile-type for a single type, decompile-assembly for full project, and search-source for pattern matching. No functional overlap.
All tool names follow a consistent lowercase hyphenated verb_noun pattern (e.g., list-types, decompile-assembly), ensuring predictability.
With 4 tools, the server is well-scoped for its domain—covering browsing, targeted decompilation, full decompilation, and source search without unnecessary redundancy.
The set covers core decompilation workflows (list, decompile single, decompile all, search). A minor gap exists for decompiling specific members without the full type, but the overall surface is sufficient for typical use.
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