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A practical CLI tool for tracking JSON file changes over time. Instead of keeping multiple copies of JSON files, this creates compact delta-based archives that preserve the complete history.

This tool solves a simple problem: you have a JSON file that changes regularly, and you want to track its history without storing dozens of full copies.

json-archive creates a .json.archive file next to your original JSON file. Each time you run the tool, it calculates only what changed and appends those deltas to the archive. You get complete history with minimal storage overhead.

The archive format is human-readable JSONL (not binary), making it easy to inspect, debug, and pipe into other scripts or web visualizations.

# Create initial archive from data.json (infers output: data.json.archive) json-archive data.json # Later, append changes to existing archive json-archive data.json.archive data.json # Or let it infer again (won't overwrite without --force) json-archive data.json # Safe: won't overwrite existing data.json.archive

Perfect for tracking YouTube video metadata over time:

# Download video info with yt-dlp yt-dlp --write-info-json -o "%(id)s.%(ext)s" "https://youtube.com/watch?v=..." # Create initial archive (creates videoID.info.json.archive) json-archive videoID.info.json # Later, append new observations to existing archive json-archive videoID.info.json.archive videoID.info.json # Or safely re-run (won't overwrite existing archive) json-archive videoID.info.json # Run daily in a cron job to capture changes # The archive preserves your title/description experiments and view count history

Hackable over efficient: The file format prioritizes human readability and scriptability over binary compactness. You can:

Open archives in any text editor
Grep through them for specific changes
Parse them in JavaScript without special libraries
Pipe them through standard Unix tools

Minimal workflow changes: Archive files sit next to your original JSON files with a .archive extension. Your existing scripts need minimal modification.

Compression support (as a concession)

While the core design keeps things simple and readable, the tool does work with compressed archives as a practical concession for those who need it. You can read from and write to gzip, brotli, and zlib compressed files without special flags.

Important caveat: Compressed archives may require rewriting the entire file during updates (depending on the compression format). If your temporary filesystem is full or too small, updates can fail. In that case, manually specify an output destination with -o to write the new archive elsewhere.

This works fine for the happy path with archive files up to a few hundred megabytes, but contradicts the "keep it simple" design philosophy - it's included because it's practically useful.

The format is JSONL with delta-based changes using JSON Pointer paths. For complete technical details about the file format, see the file format specification.

{"version": 1, "created": "2025-01-15T10:00:00Z", "initial": {"views": 100, "title": "My Video"}} # First observation ["observe", "obs-001", "2025-01-15T10:05:00Z", 2] ["change", "/views", 100, 150, "obs-001"] ["change", "/title", "My Video", "My Awesome Video", "obs-001"] # Second observation ["observe", "obs-002", "2025-01-15T11:00:00Z", 1] ["change", "/views", 150, 200, "obs-002"]

Each observation records:

What changed (using JSON Pointer paths like /views)
The old and new values
When it happened
A unique observation ID

The tool infers behavior from filenames:

Info command - View archive metadata and observation timeline
State command - Retrieve JSON state at specific observations
File format specification - Technical details about the archive format

# Create archive from JSON files (output inferred from first filename) json-archive file1.json file2.json file3.json # Creates: file1.json.archive # Won't overwrite existing archives (safe to re-run) json-archive data.json # Won't overwrite data.json.archive if it exists # Force overwrite existing archive json-archive --force data.json # Specify custom output location json-archive -o custom.archive data.json

# First file is archive, rest are appended json-archive existing.json.archive new1.json new2.json # Works with any mix of files json-archive data.json.archive updated-data.json

# Add snapshots after 10 observations instead of default of 100 for faster append operations json-archive -s 50 data.json # Add source metadata json-archive --source "youtube-metadata" data.json

cargo install json-archive

Or build from source:

git clone <repo> cd json-archive cargo build --release

Archives use the .json.archive extension by default:

data.json -> data.json.archive
video.info.json -> video.info.json.archive
config.json -> config.json.archive

This makes it immediately clear which files are archives and which are source files.

The tool uses descriptive diagnostics instead of cryptic error codes:

error: I couldn't find the input file: missing.json | = help: Make sure the file path is correct and the file exists. Check for typos in the filename.

Diagnostics are categorized as Fatal, Warning, or Info, and the tool exits with non-zero status only for fatal errors.

Performance characteristics

Memory usage: Bounded by largest single JSON file, not archive size
Append speed: Fast - only computes deltas, doesn't re-read entire archive
Read speed: Linear scan, but snapshots allow seeking to recent state
File size: Typically 10-30% the size of storing all JSON copies

For very large archives, consider using snapshots (-s flag) to enable faster seeking.

Archives can be loaded directly in web applications:

// Parse archive in browser fetch('data.json.archive') .then(response => response.text()) .then(text => { const lines = text.split('\n'); const header = JSON.parse(lines[0]); const events = lines.slice(1) .filter(line => line && !line.startsWith('#')) .map(line => JSON.parse(line)); // Replay history, build visualizations, etc. });

The format uses only standard JSON. No special parsing required.

This is a practical tool built for real workflow needs. Contributions welcome, especially: