binlog-generation

Generate Binary Logs

Scope and routing

Generate MSBuild binary logs (binlogs) for build diagnostics and analysis. USE FOR: adding /bl:{} to any dotnet build, test, pack, publish, or restore command to capture a full build execution trace, prerequisite for binlog-failure-analysis and build-perf-diagnostics skills, enabling post-build investigation of errors or performance. Requires MSBuild 17.8+ / .NET 8 SDK+ for {} placeholder; PowerShell must quote the complete switch as '-bl:{}'. DO NOT USE FOR: non-MSBuild build systems (npm, Maven, CMake), analyzing an existing binlog (use binlog-failure-analysis instead).

Pass the /bl switch when running any MSBuild-based command. This is a non-negotiable requirement for all .NET builds.

Commands That Require /bl

You MUST add the /bl:{} flag to:

• dotnet build
• dotnet test
• dotnet pack
• dotnet publish
• dotnet restore
• msbuild or msbuild.exe
• Any other command that invokes MSBuild

Preferred: Use {} for Automatic Unique Names

Note: The {} placeholder requires MSBuild 17.8+ / .NET 8 SDK or later.

The {} placeholder in the binlog filename is replaced by MSBuild with a unique identifier, guaranteeing no two builds ever overwrite each other — without needing to track or check existing files.

# Every invocation produces a distinct file automatically
dotnet build /bl:{}
dotnet test /bl:{}
dotnet build --configuration Release /bl:{}

PowerShell requires quoting the complete switch:

# Keep the literal {} placeholder in one argument
dotnet build '-bl:{}'
dotnet test '-bl:{}'

Why This Matters

1. Unique names prevent overwrites - You can always go back and analyze previous builds
2. Failure analysis - When a build fails, the binlog is already there for immediate analysis
3. Comparison - You can compare builds before and after changes
4. No re-running builds - You never need to re-run a failed build just to generate a binlog

Examples

# ✅ CORRECT - {} generates a unique name automatically (bash/cmd)
dotnet build /bl:{}
dotnet test /bl:{}

# ✅ CORRECT - quote the complete PowerShell argument
dotnet build '-bl:{}'
dotnet test '-bl:{}'

# ❌ WRONG - Missing /bl flag entirely
dotnet build
dotnet test

# ❌ WRONG - No filename (overwrites the same msbuild.binlog every time)
dotnet build /bl
dotnet build /bl

One build = one binlog

Add /bl:{} to every MSBuild invocation separately — never reuse a name and never rely on bare /bl:

• Building several configurations, projects, or retrying a failed build? Each command still gets its own /bl:{} so the logs never overwrite each other.

dotnet build -c Debug   /bl:{}   # unique file
dotnet build -c Release /bl:{}   # another unique file

Verify the binlog exists

After the build, confirm a .binlog was actually produced before moving on to analysis — a build that fails before MSBuild starts (e.g. a bad argument) writes no binlog:

ls -1 *.binlog       # bash
dir /b *.binlog      # Windows cmd

Get-ChildItem *.binlog   # PowerShell

Note the resulting path so binlog-failure-analysis or build-perf-diagnostics can consume it.

When a Specific Filename Is Required

If the binlog filename needs to be known upfront (e.g., for CI artifact upload), or if {} is not available in the installed MSBuild version, pick a name that won't collide with existing files:

1. Check for existing *.binlog files in the directory
2. Choose a name not already taken (e.g., by incrementing a counter from the highest existing number)

# Example: directory contains 3.binlog — use 4.binlog
dotnet build /bl:4.binlog

Cleaning the Repository

When cleaning the repository with git clean, always exclude binlog files to preserve your build history:

# ✅ CORRECT - Exclude binlog files from cleaning
git clean -fdx -e "*.binlog"

# ❌ WRONG - This deletes binlog files (they're usually in .gitignore)
git clean -fdx

This is especially important when iterating on build fixes - you need the binlogs to analyze what changed between builds.