Binlog Analysis

Binlog Analysis (via the binlog-mcp MCP server)

Boil a failed build down to root causes. This skill does two small things and delegates the heavy lifting to an MCP server:

1. Fetch the build's *.binlog — from your local build, or from a failed fsharp-ci Azure DevOps PR build (downloads the published artifact).
2. Hand the path to the binlog-mcp MCP server (Microsoft.AITools.BinlogMcp), which queries the binlog live (≈38 tools): structured errors, categorized root causes, and an MSBuild X-ray (target/task/analyzer timings, incrementality, double-writes, …).

Because the analysis lives in the MCP server, this skill stays tiny — and gets better automatically as that server gains features.

When to use

• A local build (with -bl) or a failed fsharp-ci PR build broke and you need to know why — compile / restore / analyzer / WarnAsError errors, or build perf.

When NOT to use

• Test failures or CheckCodeFormatting. The build binlog has no errors in that case: binlog_overview will show the build succeeded / 0 errors — stop and use pr-build-status / flaky-test-detector instead.

Step 1 — get the binlog path

# Local: newest *.binlog under <repo>/artifacts/log (build first, e.g. ./build.sh --binaryLog)
pwsh .github/skills/binlog-analysis/scripts/Get-Binlog.ps1

# Local: a specific file, directory, or glob
pwsh .github/skills/binlog-analysis/scripts/Get-Binlog.ps1 -BinlogPath artifacts/log/Debug/Build.binlog

# Azure DevOps: latest FAILED fsharp-ci build for a PR (downloads + keeps the binlog)
pwsh .github/skills/binlog-analysis/scripts/Get-Binlog.ps1 -PrNumber 19941

# Azure DevOps: explicit build id; -AllLegs for every leg; -Json for a path list
pwsh .github/skills/binlog-analysis/scripts/Get-Binlog.ps1 -BuildId 1462217 -Json

It prints the resolved *.binlog path(s) (Azure DevOps artifacts are downloaded to a temp folder and kept so the MCP can read them).

Step 2 — analyze via the binlog-mcp MCP tools

With each path, call the MCP server (the argument is binlog_file):

• binlog_overview — build status + error/warning counts. Call this first to decide whether there's anything to analyze.
• binlog_diagnose — categorized root causes + next-step hints.
• binlog_errors / binlog_warnings — structured diagnostics (code / file / line / column / project).
• binlog_search — free-form drill-down.
• Perf: binlog_expensive_targets / binlog_expensive_tasks / binlog_expensive_analyzers, binlog_incremental_analysis, binlog_double_writes, binlog_target_graph.

Multi-targeting note. Today binlog_errors returns one row per target framework, so a single source error in a multi-TFM project (e.g. FSharp.Compiler.Service → net10.0;netstandard2.0) appears once per TFM. A lossless dedup (code,file,line → set of TFMs) is proposed upstream in dotnet-microsoft/ai-tools; when it lands, this skill gets the deduped view for free — no change here.

Prerequisites

• The binlog-mcp MCP server registered with your agent. The tool is pinned in the repo's .config/dotnet-tools.json (Microsoft.AITools.BinlogMcp); run dotnet tool restore once, then register it as an MCP server. For example, Copilot CLI (~/.copilot/mcp-config.json):

  { "mcpServers": { "binlog-mcp": {
      "command": "dotnet", "args": ["tool", "run", "binlog-mcp"],
      "tools": ["*"], "deferTools": "auto" } } }
  

  (gh-aw: a mcp-servers: block; VS Code: .vscode/mcp.json. Telemetry is on by default — opt out with DOTNET_CLI_TELEMETRY_OPTOUT=1 if desired.)
• PowerShell 7+ (pwsh) and a .NET 10 SDK (already required by the repo).
• Azure DevOps modes need network access to dev.azure.com.