WARC

Definition

WARC, the Web ARChive format, is an ISO standard file format for storing web captures. Each record holds a raw HTTP request or response plus metadata such as the capture time and target address, so a page can be examined or replayed exactly as it was collected.

In plain terms

Libraries and web archives use WARC to preserve pages. A file is a sequence of records; each has a short header (what kind of record, which address, which moment) followed by the verbatim content, headers and body included. Files can be compressed.

For research the value is raw evidence kept before parsing. If the parser improves, you can read the original again instead of asking a source that may have changed or vanished, and you can show what was seen and when. Raw copies are large and may be restricted by a licence or retention limit (see Data License).

Example

The start of one record in a WARC file (abbreviated):

WARC/1.1
WARC-Type: response
WARC-Target-URI: https://example.org/list?page=1
WARC-Date: 2026-10-15T06:00:03Z
Content-Type: application/http; msgtype=response

Common misunderstandings

• “A screenshot is just as good.” It records pixels, not headers, structure or exact text, and it cannot be re-parsed.
• “Archived means I may keep and share it.” Keeping and redistributing are governed by rights and terms, not by the file format.
• “WARC is only for libraries.” Any project that wants replayable raw evidence can use it, or an equivalent that keeps the same facts.