Speedscope — Interactive Flame Chart Viewer for Performance Profiles

Introduction

Speedscope is a web-based performance profile viewer that renders interactive flame charts. It supports profiles from dozens of tools across many languages, making it a universal viewer for CPU and memory profiling data. It runs entirely in the browser with no server-side processing.

What Speedscope Does

• Renders flame charts, left-heavy (aggregated) views, and sandwich views
• Imports profiles from pprof, perf, Chrome DevTools, Instruments, and many more
• Provides smooth zooming and panning through large profile datasets
• Highlights individual functions across all call stacks (sandwich view)
• Runs entirely client-side with no data uploaded to any server

Architecture Overview

Speedscope is built with TypeScript and WebGL for high-performance rendering. Profile data is parsed client-side from various formats into a normalized internal model. The flame chart renderer uses WebGL to draw thousands of rectangles efficiently, enabling smooth interaction even with millions of samples. All processing happens in the browser.

Self-Hosting & Configuration

• Use the hosted version at speedscope.app (no install needed)
• Install the CLI globally with npm install -g speedscope
• Run speedscope profile.json to open a profile in your default browser
• Self-host by serving the static build output from any web server
• Pipe profiler output directly: py-spy record -o profile.json && speedscope profile.json

Key Features

• Supports 20+ profile formats across Python, Ruby, Go, Node.js, Java, and native code
• WebGL-based rendering handles profiles with millions of samples smoothly
• Three complementary views: time-ordered flame chart, left-heavy, and sandwich
• No data leaves your machine; all processing is client-side
• Keyboard shortcuts for quick navigation and function search

Comparison with Similar Tools

• Chrome DevTools — Built into Chrome but limited to Chrome profiles; Speedscope supports many formats
• Perfetto UI — Powerful trace viewer; Speedscope is lighter and focused on flame charts
• FlameGraph (Brendan Gregg) — Generates static SVGs; Speedscope provides interactive exploration
• pprof web UI — Go-specific; Speedscope supports profiles from any language

FAQ

Q: Is my profile data uploaded anywhere? A: No. All processing happens in the browser. Your data never leaves your machine.

Q: What profile formats are supported? A: pprof, Chrome DevTools, Instruments, perf, collapsed stacks, Pyinstrument, VizTracer, and many more.

Q: Can I use it offline? A: Yes. Install via npm and run locally, or download the static build for fully offline use.

Q: How does the sandwich view work? A: It shows a selected function in the center, with callers above and callees below, aggregated across all occurrences.

Sources

• https://github.com/jlfwong/speedscope
• https://www.speedscope.app/