Introduction
DEFLATE is the compression algorithm specified in RFC 1951 and powers gzip (RFC 1952), zlib (RFC 1950), and PNG image encoding. Every web browser supports it natively via Content-Encoding: gzip. If you need to compress data before transmission or decompress a DEFLATE stream you received, this tool handles both directions in your browser. It uses the pako library, which is the most widely used JavaScript implementation of DEFLATE. No data is sent to any server.
What this tool does
- Compresses text into DEFLATE streams (RFC 1951 raw format)
- Decompresses DEFLATE streams back to the original text
- Outputs compressed data in both hex and base64 formats
- Accepts hex or base64 input when decompressing (auto-detected)
- Uses the pako library, a JavaScript port of zlib
How this tool works
The tool uses pako, which implements DEFLATE in pure JavaScript. In compress mode, it encodes the input text as UTF-8 bytes using TextEncoder, passes them to pako.deflate(), and outputs the result as both a hex string and a base64 string. In decompress mode, it auto-detects whether the input is hex (only hex characters) or base64, converts it to a Uint8Array, passes it to pako.inflate(), and decodes the result as UTF-8. The tool updates output on every keystroke. There is no size limit imposed by the tool itself, but very large inputs may cause the browser to become temporarily unresponsive since DEFLATE is a synchronous operation.
How DEFLATE compression works
DEFLATE combines two algorithms: LZ77 compression and Huffman coding. LZ77, published by Abraham Lempel and Jacob Ziv in 1977, replaces repeated byte sequences with references to earlier occurrences (distance/length pairs). Huffman coding, developed by David Huffman in 1952, replaces fixed-size byte representations with variable-length codes where frequent symbols get shorter codes. DEFLATE uses a sliding window of 32 KB for LZ77 and dynamic Huffman tables that are optimized per block. The format supports three block types: stored (no compression), fixed Huffman (predefined code tables), and dynamic Huffman (custom tables encoded in the block). Most compressors use dynamic Huffman for best ratio. The pako library implements all three block types and achieves compression ratios comparable to native zlib.
How to use this tool
- Select mode: Deflate (compress) or Inflate (decompress).
- For compression: type or paste text in the input box. Output appears as hex and base64.
- For decompression: paste hex or base64 encoded DEFLATE data. The tool auto-detects the format.
- Use the Swap button to switch between compression and decompression modes.
- Copy the output using the Copy result button.
Real-world examples
Compressing API response data
A JSON API response of 2 KB can be compressed to roughly 400 bytes with DEFLATE, a 5x reduction. This is useful for storing compressed payloads in localStorage or transmitting over WebSocket. Compress the JSON string and store the base64 output, then decompress when reading it back.
Decompressing a gzip payload
If you receive a raw DEFLATE stream (not wrapped in gzip headers), paste the hex or base64 data and switch to Inflate mode. The tool returns the original text. Note: gzip-wrapped data uses pako.gunzip() or pako.ungzip() rather than raw inflate.
Inspecting PNG compressed chunks
PNG files store image data in IDAT chunks compressed with DEFLATE. If you extract the compressed data from an IDAT chunk (after the 2-byte zlib header), you can decompress it here to inspect the raw scanline data. This is useful for debugging PNG encoding issues.
Comparison with similar methods
| Method | Complexity | Typical use |
|---|---|---|
| DEFLATE (RFC 1951) | LZ77 + Huffman | gzip, zlib, PNG |
| Brotli (RFC 7932) | LZ77 + 2nd order context | HTTP Content-Encoding |
| Zstandard | LZ77 + FSE + entropy | High-speed compression |
| LZMA | LZ77 + range coding | 7z, xz archives |
Limitations or considerations
DEFLATE is a lossless compression algorithm, but it does not compress all data effectively. Already-compressed data (JPEG, MP4, ZIP files) will not shrink and may even grow slightly. The tool processes data synchronously, so very large inputs (over 50 MB) may freeze the browser tab. For production use, consider Web Workers to avoid blocking the UI thread.
Frequently asked questions
What is the difference between DEFLATE, gzip, and zlib?
DEFLATE (RFC 1951) is the raw compression algorithm. zlib (RFC 1950) wraps DEFLATE with a header and checksum. gzip (RFC 1952) wraps DEFLATE with a different header, filename, and CRC32 checksum. This tool uses raw DEFLATE via pako.deflate()/inflate().
Why does my compressed output look longer than the input?
Short inputs (under 100 bytes) often produce longer output because the Huffman table overhead exceeds the compression savings. DEFLATE is designed for larger inputs where repeated patterns can be exploited.
Is pako compatible with Python's zlib?
Yes. pako.deflate() produces the same format as Python's zlib.compress(). You can decompress data compressed by Python and vice versa, as long as you use the same wrapper format (raw, zlib, or gzip).
Can I use this to compress files?
The tool accepts text input. For binary files, you would need to read the file as an ArrayBuffer and pass it to pako directly. This tool is designed for text compression and decompression.
Conclusion
DEFLATE remains the most widely supported compression algorithm on the web. This tool provides instant compression and decompression using the pako library, with output in hex and base64. Use it for debugging compressed payloads, inspecting PNG data, or reducing text size for storage and transmission.