fast-cli

A blazingly fast CLI tool for testing internet speed uses fast.com v2 api. Written in Zig for maximum performance.

⚡ 1.2 MB binary • 🚀 Zero runtime deps • 📊 Adaptive stability-based stopping

Demo

Why fast-cli?

• Tiny binary: Just 1.2 MB, no runtime dependencies
• Blazing fast: Concurrent connections with adaptive chunk sizing
• Cross-platform: Single binary for Linux, macOS
• Smart stopping: Uses a ramp + steady stability strategy and stops on stable speed or max duration

Supported Platforms

• Linux: x86_64, aarch64 (ARM64)
• macOS: x86_64 (Intel), aarch64 (aka Apple Silicon)
• Windows: x86_64 (release binary zip)

Installation

Quick Install

curl -sSL https://raw.githubusercontent.com/mikkelam/fast-cli/main/install.sh | bash

install.sh currently supports Linux and macOS only (not Windows yet).

Pre-built Binaries

For example, on an Apple Silicon Mac:

curl -L https://github.com/mikkelam/fast-cli/releases/latest/download/fast-cli-aarch64-macos.tar.gz -o fast-cli.tar.gz
tar -xzf fast-cli.tar.gz
chmod +x fast-cli && sudo mv fast-cli /usr/local/bin/
fast-cli --help

Build from Source

git clone https://github.com/mikkelam/fast-cli.git
cd fast-cli
zig build -Doptimize=ReleaseSafe

Usage

fast-cli - Estimate connection speed using fast.com

USAGE:
    fast-cli [OPTIONS]

OPTIONS:
    -h, --help                        Display this help and exit.
        --https                       Use HTTPS when connecting to fast.com (default)
        --no-https                    Use HTTP instead of HTTPS
    -u, --upload                      Check upload speed as well
    -j, --json                        Output results in JSON format
    -d, --duration <usize>            Maximum test duration in seconds (effective range: 7-30, default: 30)

Example Output

$ fast-cli --upload
🏓 25ms | ⬇️ Download: 114 Mbps | ⬆️ Upload: 62 Mbps

$ fast-cli -d 15  # Quick test with 15s max duration
🏓 22ms | ⬇️ Download: 105 Mbps

$ fast-cli -j     # JSON output
{"download_mbps": 131, "ping_ms": 20.8, "upload_mbps": null, "error": null}

Stability Strategy

The speed test uses a two-phase strategy:

1. Ramp phase: increase active workers based on observed throughput.
2. Steady phase: lock worker count and estimate authoritative speed.

The test stops when either:

• speed is stable within a configured delta threshold over recent steady samples, or
• max duration is reached.

Development

Optional: use mise to install and run the project toolchain.

mise install
mise exec -- zig build test

# Debug build
zig build

# Run tests
zig build test

# Release build
# Consider removing -Dcpu if you do not need a portable build
zig build -Doptimize=ReleaseFast -Dcpu=baseline

License

MIT License - see LICENSE for details.

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Not affiliated with Netflix or Fast.com