roslyn-mcp-overview

RoslynMcpServer overview

MCP server (stdio) for C# analysis: Roslyn workspaces + ILSpy decompile. TFM net10.0, version in RoslynMcpServer.csproj (currently 1.5.15). Package id RoslynMcpServer. Self-contained publish for win/osx/linux RIDs.

Layout

• Program.cs — MSBuild bootstrap, optional ROSLYN_MCP_WORKSPACE → cwd, Serilog to logs/mcp-*.log under AppContext.BaseDirectory (each line prefixed with a harness session id)
• Hosting/ — DI (AddRoslynMcpServerTools), McpToolRegistry
• Tools/ — MCP tool classes (Workspace, CodeAnalysis, Skeleton, Build, Run, Test, NuGet, Utility, …)
• Services/ — Workspace (SolutionManager), Analyzers, Build, Editing, Navigation, Resolve, Testing; helpers that do not belong to one of those stay at the root
• Diagnostics/ — parsers (build, VSTest, NuGet audit), SDK mismatch, MSBuild locator
• RoslynMcpServer.Tests/ — xUnit; InternalsVisibleTo
• Docs: README.md (EN+RU), AGENTS.md.sample (copy to app repos as AGENTS.md)

DI / tools

Tools are singletons registered in RoslynMcpServiceCollectionExtensions. Inject SolutionManager — do not new workspaces/HTTP. Heavy services via constructor.

Related consumer

Real-world validation often uses BrqMover (c:\Devel\BrqMover) — app repo with its own AGENTS.md; do not hardcode that path into this repo’s docs/rules.

Version history (agent-relevant)

• 1.5.7 — Linux SDK fallback also searches /usr/lib/dotnet and ~/.dotnet. Missing-SDK messages name DOTNET_ROOT/PATH off Windows. get_mcp_server_info publishes with the current process RID. Analyzer path keys are case-sensitive off Windows
• 1.5.6 — a watcher event during the additional-file or .editorconfig content read no longer drops that save for the rest of the flush. The flush reads the path again a few times and publishes only after the bytes are accepted. An unstable, unreadable, missing, or still-open own write stays deferred
• 1.5.4 — saved additional-file and analyzer-config text is applied on the published snapshot (WithAdditionalDocumentText / WithAnalyzerConfigDocumentText) during the same flush as .cs. Not TryApplyChanges. XAML, resx, Razor, evaluation-input paths, and new or deleted files stay out. Coverage-unknown does not block a document already in the graph and is not cleared by the replace
• 1.5.3 — DLL tests share one solution-target buildPolicy (auto / always / never) on run_dotnet_test, run_specific_test, and run_test_by_filter when binariesPath is set
• 1.5.2 — disk watcher follows the loaded graph: recursive project directories, non-recursive watches for linked files and walk-up props outside them. One user .cs text updates every document of that path. Non-C# inputs are recorded by role and are not text-synced. Own writes match saved bytes, including BOM. Semantic flush does not clear input revisions. search_code roots are unchanged
• 1.5.1 — WPF {ProjectName}_{random}_wpftmp.csproj create/delete does not mark the project graph stale unless that path is a loaded project. A real project-file change during the build still does
• 1.5.0 — MCP C# SDK 2.2.0. Group enablement batches tools/list_changed with the SDK DeferChangedEvents scope. 2025-11-25 sessions receive that notification directly; 2026-07-28 sessions receive it after subscriptions/listen (toolsListChanged). Plugin projects reference ModelContextProtocol 2.2 (Major.Minor must match the host assembly)
• 1.4.19 — disk watcher error and directory-rename callbacks still request a full re-read when the logger throws (Logger.Log rethrows a provider failure such as Windows Event Log ObjectDisposedException); the callback no longer kills the process
• 1.4.18 — plugins: IRoslynMcpPlugin assemblies load before Build from plugins/<id>/, the plugins key of RoslynMcp.jsonc, or ROSLYN_MCP_PLUGINS (dev directory shadow-copied); a plugin that cannot be loaded is skipped with [RoslynMcp] plugin skipped (<id or path>): <reason> on stderr and in logs/mcp-*.log while the host still starts; get_mcp_server_info lists loaded plugins and skips, get_tool_help reports Kind/Group plugin from the start report; plugin tools are in tools/list and Registered MCP tools, not in McpToolCatalog or list_tool_groups, and lite/full do not filter them
• 1.4.17 — get_changed_files reads git stdout and stderr together, closes stdin, and stops the process after 180s plus up to 3s of cleanup (Kill(entireProcessTree) on Windows, Linux, and macOS)
• 1.4.16 — shared logs/mcp-*.log lines include a harness session id ([cursor-k7m2], [opencode-4mht]): parent exe name, or node command-line package/directory; 4-char suffix; unknown parent is cli; command line is not logged
• 1.4.15 — writes preserve the file's BOM state (no BOM added to BOM-free files, none stripped from BOM files); SourceTextEncoding resolves existing document → candidate → on-disk BOM
• 1.3.32 — DotNetCliRunner timeout kills the process then drains pipes (no hang on canceled ReadToEndAsync); lifecycle host build honors TimeoutMs
• 1.3.31 — update_file_content / apply_patch do not recreate missing-on-disk .cs; disk-sync does not WithDocumentText a deleted known document
• 1.3.30 — disk-sync updates texts of known documents only (no AddDocument/RemoveDocument); new/deleted .cs → composition-stale + reload, not <Compile Include> / NETSDK1022
• 1.3.29 — single TestAttributeMatcher (base-chain walk) shared by get_test_list and run_specific_test; custom FactAttribute-derived attributes ([AnalyzerLifecycleFact], [WpfFact]) discovered and filterable; DataRowAttribute no longer a test marker; get_test_list adds totalTestMethodsFound (before filters) and only blames filters when the workspace did find tests
• 1.3.28 — get_test_list discovered 0 tests on every real workspace: GetSymbolInfo(AttributeSyntax).Symbol is the attribute constructor (.ctor), and names were compared without the Attribute suffix (Fact vs FactAttribute); now resolves ContainingType + strips suffix/qualifier, syntactic fallback only when unbound; TestDiscoveryHelperTests fixtures now reference corelib + System.Runtime + xunit.core so attributes actually bind (they were false-green)
• 1.3.27 — run_dotnet_test / run_specific_test / run_test_by_filter / run_dotnet_run emit the same MCP progress heartbeats as build (dotnet build / dotnet test / dotnet run; 5 s; no stdout); RunSeparatedAsync takes optional CliProgressWatch
• 1.3.26 — progress elapsed = current step only (boundary = starting); numeric Progress = strictly increasing whole seconds, no Total (not a percentage); adapter detects SDK no-op progress so a token-less call starts no timer
• 1.3.25 — run_dotnet_build emits MCP notifications/progress heartbeats (step label, elapsed, previous exit; no stdout) via a reusable DotNetCliRunner/DotNetBuildProbe seam; no schema change, no host-timeout fix
• 1.3.24 — test tools include VSTest Standard Output/Error (ConversationId, ITestOutputHelper) with per-stream budgets; includeFullOutput / maxOutputChars
• 1.3.23 — run_specific_test matches xUnit method-only / FQN(args) display names (dot-bounded suffix); slow durations [3 m 8 s] valid
• 1.3.22 — test failure text keeps multiline Error Message:; MSBuild Build FAILED / 0 Error(s) footer after failed tests is not compile/silent failure
• 1.3.21 — U-ARB-01: inaccessible original analyzer path is skip (no rewrite, not missing)
• 1.3.20 — preserve DependencyUnsupported / main-only through a full publication ban (v3 S8)
• 1.3.19 — mixed analyzer prepare: per-reference applied/excluded/banned publication (v3 S5), no HasAnyApplied
• 1.3.18 — withhold opt-in semantics when provenance capture unsuitable (V3-R3); cached true does not repair
• 1.3.17 — persistent fail-closed publication after a failed opt-in (V3-R2)
• 1.3.16 — reject stale write bases before any disk/workspace mutation (V3-R1 / A4-09)
• 1.3.15 — no implicit semantic workspace load (FindDocumentAsync; U-ARB-04-IMPL-1)
• 1.3.14 — atomic analyzer load/prepare boundary (U-ARB-04)
• 1.3.13 — shadowCopyInSolutionAnalyzers activation is session-sticky (U-ARB-05); disable via reset_workspace
• 1.3.12 — analyzer provenance acceptance (E5-S4)
• 1.3.11 — analyzer provenance diagnostics: stable internal reason codes (E5-S3)
• 1.3.10 — analyzer provenance rollout: exact load-session F-09 join only (E5-S2)
• 1.3.9 — analyzer provenance capture via design-time binlog replay (F-09)
• 1.3.8 — workspace write boundary (epoch 4): preflight → exact inverse → persist → apply/reconciliation
• 1.3.7 — overlay loader contract: restart-required, main-only (epoch 3)
• 1.3.6 — immutable content-hashed analyzer generation mapping (epoch 2); zero analyzer I/O on edit
• 1.3.5 — overlay fix: shadow rewrite stays in-memory, never TryApplyChanges (v1.3.4 corrupted real .csproj)
• 1.3.4 — load_workspace shadowCopyInSolutionAnalyzers (superseded by 1.3.5)
• 1.3.3 — load_workspace logProjectOutputDiagnostics
• 1.3.2 — binariesPath on run_specific_test / run_dotnet_test; run_test_by_filter honors noBuild
• 1.3.1 — get_test_list projectName / nameContains filters
• 1.3.0 — run_test_by_filter (raw VSTest --filter)
• 1.2.3 — run_dotnet_build projectName (sln -t virtual path); -p:Configuration in probes
• 1.2.2 — load_workspace briefOutput
• 1.2.1 — load_workspace buildArgs (session-cached; build only)
• 1.2.0 — tool profiles full / lite, ROSLYN_MCP_TOOL_GROUPS, list_tool_groups / get_tool_help / enable_tool_group
• 1.1.1 — decompile assemblyName: dotted simple names (Spectre.Console) no longer truncated
• 1.1.0 — disk watcher: saved .cs (IDE/git) sync into MSBuildWorkspace before symbol search; no keystroke/unsaved buffers; .csproj changes skip load cache, not OpenSolutionAsync from the watcher
• 1.0.35 — Roslyn 5.9.0; dedicated VS 2026 / MSBuild 18 BuildHost (XMakeElements) load/symbol failure (not SDK mismatch)
• 1.0.34 — load_workspace: wrapped design-time MSBuild warnings (ASPDEPR007 / IncludeOpenAPIAnalyzers, MSB3270, analyzer metadata refs) are warnings, not hard Failure
• 1.0.33 — load_workspace optional targetFramework (inner TFM for CrossTargeting / TargetFrameworks); dedicated missing-Compile load report
• 1.0.32 — run_specific_test: VSTest Passed/Failed lines accept [1 s] / [1 m 28 s] durations (not only ms)
• 1.0.31 — run_dotnet_test / run_specific_test: separate incremental dotnet build then dotnet test --no-build (parser sees test output only)
• 1.0.30 — apply_patch replaceAll: advance past inserted text (hang when newString contains oldString)
• 1.0.29 — load_workspace optional Configuration/Platform (cached for build/test); empty-TFM ResolvePackageAssets dedicated fail
• 1.0.28 — run_dotnet_test: infer Passed when .slnx VSTest omits the Passed: line
• 1.0.27 — load_workspace: NU1701 / TFM-compat restore warnings soft (not fatal); Msbuild failed wrapper word failed is not blocking by itself
• 1.0.26 — agent diagnostics: client-abort load_workspace, empty get_test_list, run_specific_test path/filter mismatch hints
• 1.0.25 — run_dotnet_build: default --no-incremental; effective exit = last build step (restore cannot mask)
• 1.0.22 — run_specific_test: VSTest-safe method filters (~, no (), no bogus leading . on dotted FQNs)
• 1.0.21 — load_workspace: NuGet prune / unused PackageReference advisories soft (warnings), not hard Failure
• 1.0.20 — optional configuration (-c) on run_dotnet_build / run_dotnet_test / run_specific_test
• 1.0.19 — .slnx accepted by load_workspace / build / test / discovery (prefer solution files for multi-config)
• 1.0.18 — tool [Description] accuracy pass (build probe, decompile resolve, NuGet timeouts, AST params)
• 1.0.17 — run_dotnet_test / run_specific_test optional noBuild / noRestore
• 1.0.15 — search_code caseSensitive; no-workspace candidate paths; rename_project; branding recipe in AGENTS
• 1.0.14 — run_dotnet_run, run_nuget_audit, get_changed_files, workspace health on load_workspace
• 1.0.13 — exact assembly resolve (deps.json + NuGet), no fuzzy Contains
• 1.0.10+ — SDK pin from global.json, build probe, VSTest parser, MCP_MSBUILD_SDK_MISMATCH