Binlog Failure Analysis Agent Skill

Analyze MSBuild binary logs to diagnose build failures. USE FOR: build errors that are unclear from console output, diagnosing cascading failures across multi-project builds, tracing MSBuild target execution order, and generally any MSBuild build issues. Requires an existing .binlog file. DO NOT USE FOR: generating binlogs (use binlog-generation), non-MSBuild build systems.

732 tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

1034

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/microsoft/testfx --skill binlog-failure-analysis

The instruction itself

6 sections, as written by the author

Analyzing MSBuild Failures with Binary Logs

This skill diagnoses MSBuild build failures from a .binlog file. The preferred

path uses the binlog MCP server (Microsoft.AITools.BinlogMcp, exposed under the

binlog MCP namespace) which is bundled with this plugin. If the MCP server is

not available, fall back to the binlog replay workflow at the bottom.

Primary workflow — binlog MCP

The MCP server exposes structured tools for inspecting a .binlog without

parsing text logs. Call them directly instead of replaying the binlog to a text

file. Call tools/list for the MCP first if you are unsure which tools are available.

Important constraints:

The .binlog file is a binary format — do NOT try to cat, head, strings, or read it directly. Use only the MCP tools to query it.
The original source/project files might or might NOT be available on disk. Project files (.csproj, .props, .targets, App.config, etc.) - if you cannot locate them on disk, they can only be read from within the binlog via MCP tools (e.g., embedded/source file retrieval).
Synthesize findings as you go. Do not spend all available time investigating — once you have enough evidence, present your conclusions. A partial answer with clear reasoning is better than timing out mid-investigation.

Use the available MCP server tools to query the binary log for:

Build errors and warnings
MSBuild properties and their values
MSBuild items (PackageReference, ProjectReference, etc.)
Project evaluation data
Target execution details
File contents embedded in the binlog

Fallback workflow — text-log replay (when MCP is unavailable)

Use this only when the MCP server cannot be started (for example, on an older

SDK or in an offline environment without access to the dotnet-tools NuGet feed).

Replay the binlog to text logs

dotnet msbuild build.binlog -noconlog \
  -fl  -flp:v=diag;logfile=full.log;performancesummary \
  -fl1 -flp1:errorsonly;logfile=errors.log \
  -fl2 -flp2:warningsonly;logfile=warnings.log

> PowerShell note: Use -flp:"v=diag;logfile=full.log;performancesummary"

> (quoted semicolons).

Search the text logs

cat errors.log
grep -n -B2 -A2 "CS0246" full.log
grep -i "CoreCompile.*FAILED\|Build FAILED\|error MSB" full.log
grep 'Target "CoreCompile"' full.log | grep -oP 'project "[^"]*"'

Generating a binlog (only if none exists)

dotnet build /bl:build.binlog

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How to use it

Copy the folder

Take microsoft/binlog-failure-analysis from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

Check the name does not clash

The agent identifies a skill by the name field in its header. Two skills with the same name cannot sit side by side — one of them will be ignored.