# Speedscope — Interactive Flame Chart Viewer for Performance Profiles

> A fast, web-based viewer for performance profiles that renders flame charts, left-heavy views, and sandwich views from many profiler formats.

## Install

Save in your project root:

# Speedscope — Interactive Flame Chart Viewer for Performance Profiles

## Quick Use
```bash
npm install -g speedscope
speedscope profile.json
# or open https://www.speedscope.app in a browser and drag-drop a profile
```

## 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/

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Source: https://tokrepo.com/en/workflows/asset-75a7642f
Author: AI Open Source