ultra

Ultra

Ultra is an advanced profiler for .NET Applications available on Windows, Linux and macOS (Apple Silicon).

📽️ Check this video for a quick tour of ultra! 📽️

✨ Features

• Sampling profiler - ETW based on Windows (up to 8190 samples/second), kernel perf events on Linux (up to 8190 samples/second, launch or attach), in-process sampler over EventPipe on macOS ARM64 (up to 1000 samples/second)
• UI based on https://profiler.firefox.com/
  • Traces shareable online: Check this example: ✨ https://share.firefox.dev/3Cya7YW ✨
  • Timeline visualization
  • Flamegraph / Stack Chart visualization
  • Call Tree visualization
  • Marker Chart and Marker Table visualization
• Precise kernel, native and managed function call stacks
• Categorization of functions:
  • .NET, .NET JIT, .NET GC, .NET CLR, Native, Kernel
• .NET GC Memory track
• JIT Compile Time Event Markers
  • See which function is getting compiled
• GC Events Markers
  • GC Allocation Ticks: Details about allocations.
  • GCHeapStats: Statistics about the GC
  • GCSuspendEE, GCRestartEE, GC Start, GC Stop events
• Lightweight trace files - e.g. Generates only a few MB for 10s
• Built for AI agents and automation:
  • ultra mcp: an MCP server to capture profiles and analyze them (call trees, hotspots, callers, markers...)
  • ultra guide: the workflow for agents and scripts, ultra report: a text overview of a profile
  • --elevate (UAC prompt from a non-admin shell on Windows), --result-file (JSON summary), --stop-file
• Requires net8.0+ via dotnet global tool

Screenshot of a trace generated by ultra visualized with https://profiler.firefox.com. Check this trace online here!

🧑‍💻 Usage

You need to have installed a .NET 10.0+ SDK

$ dotnet tool install -g Ultra # The command ultra.exe will be available from your PATH

Windows

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🚨 The profiler requires to run from an elevated prompt with administrative rights 🚨

This is required to allow to collect full stack traces, including kernel and native functions.

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Example: open a terminal with administrative rights, to profile an executable called my_commands.exe:

$ ultra.exe profile -- my_command.exe arg0 arg1 arg2...

⚠️ Notice the -- separator to separate the arguments to ultra.exe from the arguments to the profiled application.

From a terminal without administrative rights, add --elevate: Windows asks for them with a UAC prompt, and the profiling runs in an elevated ultra relayed to your terminal (a launched program still runs as you, not elevated):

$ ultra.exe profile --elevate -- my_command.exe arg0 arg1 arg2...

Profiling a running application just requires the PID of the process to profile:

$ ultra.exe profile 15243 # PID of the process to profile
# Wait for a bit and press only one CTRL+C to stop the profiling

macOS (Apple Silicon)

On macOS, no elevated privileges are required. The profiler injects a small sampler library into the launched process to collect native and managed call stacks.

$ ultra profile -- my_command arg0 arg1 arg2...

Current limitations on macOS:

• Only ARM64 (Apple Silicon) is supported.
• Only launching a program is supported - attaching to a running process with a PID is not (the sampler library can only be injected at process startup).
• The maximum sampling frequency is 1000 samples/second (--sampling-interval minimum is 1ms).
• Kernel call stacks are not collected (user-space native and managed call stacks are).
• Symbols of system libraries living in the dyld shared cache (e.g. libsystem_pthread.dylib) are not resolved.

🤖 AI agents and automation

ultra guide prints the workflow for AI agents and scripts. In short:

$ ultra profile --elevate --duration 30 --result-file result.json --pid 1234   # capture, JSON summary with the profile files
$ ultra report ultra_my_app_..._pid_1234.json.gz                              # text overview: CPU per thread, top functions

ultra mcp is an MCP server (stdio) that lets your AI coding agent capture profiles (find_processes, start_profiling, get_job_status, stop_job...) and analyze them (get_profile_report, call_tree, call_tree_inverted, find_hotspots, focus_function, query_markers...). Configure your agent to start ultra mcp, e.g. claude mcp add ultra -- ultra mcp, or in .vscode/mcp.json:

{ "servers": { "ultra": { "type": "stdio", "command": "ultra", "args": ["mcp"] } } }

The analysis tools of ultra mcp come from UltraMcp by @KirillOsenkov (MIT license, see THIRD-PARTY-NOTICES.txt).

📖 User Guide

For more details on how to use Ultra, please visit the user guide.

🪪 License

This software is released under the BSD-2-Clause license.

🤗 Author

Alexandre Mutel aka xoofx.