WARC is an archive file format which has been the predominant format for Web (HTTP) archives from 2009 to (as of 2019) the present; it is also used for archives of documents collected through other prococols (e.g. FTP), and could technically be used to store a collection of ordinary files. It is the successor to the ARC format. It was developed under the auspices of the International Internet Preservation Consortium, and standardized as ISO 28500, Information and documentation -- WARC file format. WARC was developed as an extension to ARC in part to provide better capabilities for managing Web archives for the long term, allowing for capture of more metadata about the circumstances of archiving. There are currently (2019) two versions of WARC: 1.0 and 1.1, formally ISO 28500:2007 and ISO 28500:2017, respectively.
Version 1.0 formally specified that URLs in the
WARC-Target-URI field should be surrounded in angle brackets, but erroneously did not show this in examples. Implementations largely followed the examples, with the notable exception of Wget, a popular WARC-producing program, which, since February 2016, has used the angle brackets, with the result of breaking much of the software that reads its output. The angle brackets were eliminated altogether in WARC 1.1. For more details, see , , 
WARC files are often compressed using gzip, resulting in a .warc.gz extension. In cases where the warc.gz file needs to randomly accessed (namely, as part of web archives accessible page-by-page), this will consist of one gzip stream for each WARC record, concatenated together (which makes for a valid gzip file). This allows any single record to be accessed by an offset, and (when the entire file is decompressed) also preserves the original WARC.
There is also a specification for a Web Archive Metadata File. Another (more widely-used) metadata format used with WARC files is CDX.
- The WARC Format v. 1.0
- The WARC Format v. 1.1
- Draft of ISO-DIS 28500 As circulated for ISO ballot and approval.
- WARC, Web ARChive file format, from Library of Congress resource on Sustainability of Digital Formats
- Working drafts for WARC specification
- WARC Specifications
- Test WARC Files warc.gz file from Internet Archive.
- WARC Tools (in Python)
- Some history on the Python tools is available on here on the COPTR wiki.
- warcat: Tool and library for handling Web ARChive (WARC) files.
- Warcreate (for Google Chrome)
- warcbase platform
- WARC Input and Output Formats for Hadoop
Other links and references
- The WARC File Format (ISO 28500) - Information, Maintenance, Drafts
- Slide show on WARC
- The WARC Ecosystem (Archive Team)
- Web Archive Analysis Workshop
- Warcbase Wiki
- Discussion of version 1.1, while it was under development
- Merging & Deduping WARC files
- Harvesting the Twitter Streaming API to WARC files
- The great WARC adventure: Using SIPS, AIPS, and DIPS to document SLAAPs
- WARC Work
- WARC MIME Media Type (as of now unregistered, but a suggested value exists)