WARC file format
.warc · .warc.gz · archive (web archive) · introduced 2009 by IIPC / ISO 28500
What is a WARC file?
WARC is the ISO standard for web archiving (ISO 28500). Every captured HTTP request and response, with full headers and body, becomes a record in the WARC stream. The Internet Archive and national libraries crawl billions of pages a day into WARC files, then serve them through replay engines like pywb and OpenWayback.
Most readers reach this page after double-clicking a .warc file and finding their operating system unsure what to do with it. The good news: WARC is a well-understood format with mature tooling on every major platform. It is supported in one click by mainstream archivers on Windows, macOS, and Linux.
How to extract a WARC file
Opening a .warc file is straightforward on every modern operating system. The exact steps depend on which platform you are on:
On Windows
- Locate the
.warcfile in File Explorer. - Right-click the file. If you have 7-Zip installed, choose 7-Zip → Extract Here. On Windows 11 the built-in extractor handles ZIP, 7z, RAR and several other formats directly through Extract All…
- If prompted, pick a destination folder and click Extract.
- The extracted files appear in a folder next to the original archive.
On macOS
- Find the
.warcfile in Finder. - Install The Unarchiver from the Mac App Store, or Keka for both creating and extracting.
- Right-click the file → Open With → The Unarchiver (or just double-click after Unarchiver is set as the default).
- The extracted folder appears next to the archive.
On Linux
- Use your file manager: right-click the archive → Extract Here (file-roller on GNOME, Ark on KDE).
- On the command line, run one of:
7z x archive.warc # works for almost any format
- The files appear in the current directory.
How to create a WARC file
To pack files into a .warc archive, you typically need an archiver that supports writing this format. Not every tool can create every format — for example, only WinRAR can create real RAR files. The sidebar lists the software known to read and write WARC.
On the command line, the canonical create command is:
# Use 7-Zip, PeaZip, or the format's reference tool to create .warc files.
If you regularly create archives at scale, a dedicated archive automation suite can wrap this command in scheduled jobs, integrity checks, and offsite replication.
Strengths
- ISO standardized
- Streamable
- Records full HTTP metadata
Weaknesses and limitations
- Huge files
- Indexing required for fast lookup
Typical use cases
- Internet Archive crawls
- National library web archiving
- Site-specific archival
Technical details
WARC uses the GZIP per record algorithm and is identified on disk by the magic byte sequence 57 41 52 43 2F. The standard MIME type is application/warc. The format is an open specification and is free for any use.
Frequently asked questions
Is WARC safe to open?
Archive files are containers — they are only as safe as what they contain. A .warc from a trusted source is fine; one received from a stranger can hold malicious executables, scripts, or files engineered to exploit bugs in your archiver. Always keep your archiver updated, and never run unknown executables that come out of an archive. A safe workflow is to extract into a sandbox and scan the contents before opening anything.
What is the maximum file size?
Modern implementations support archives in the multi-terabyte range. The practical limit is your filesystem (FAT32 caps at 4 GB; ext4, NTFS, APFS, and exFAT all comfortably handle multi-TB files).
Can I password-protect a WARC?
Some archivers can wrap WARC files in an encrypted container, but the format itself does not always include built-in encryption. Check your archiver's documentation.
How does WARC compare to other formats?
See our format comparison pages such as ZIP vs 7z, ZIP vs RAR, and tar.gz vs tar.xz for side-by-side feature tables.