WARC File Format (.warc)
A WARC file is a sequence of records that each capture one HTTP request and response, or another web-harvesting transaction, exactly as it crossed the wire, headers included, so a crawl can be replayed rather than merely read.
WARC at a glance#
| Full name | Web ARChive |
|---|---|
| File extension | .warc |
| Category | Archives |
| Developer | Internet Archive and the International Internet Preservation Consortium |
| First released | 2009 |
| MIME types | application/warc |
| Compression | Varies from file to file |
| Specification | ISO 28500 (WARC 1.1) |
| FileFlip support | FileFlip reads this format but does not write it |
What a .warc file can hold#
These are the things a WARC file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Embedded metadata | Yes |
|---|---|
| Streaming | Yes |
Strengths and limitations of WARC#
What WARC does well
- Records the full HTTP exchange, request and response headers included, so a crawl can be replayed exactly as the server sent it rather than just viewed as saved files
- Appends new records without touching old ones, which is why crawlers write directly to a WARC file while a crawl is still running
- ISO-standardized as ISO 28500, which is why every major web archiving tool, including the Internet Archive's, converged on it
Where WARC falls short
- Files grow large fast, since every request and response is stored in full rather than deduplicated by default
- Reading one meaningfully requires archive-aware software; a text editor shows raw HTTP traffic, not a browsable page
- Captures what a crawler received, not what a browser would render, so heavily scripted pages can archive incompletely
Use WARC when a crawl or website capture needs to preserve exactly what was sent and received, not just the resulting files.
Convert a WARC's contents to plain files when only the captured pages or media are needed and the HTTP-level record of the crawl itself does not matter.
How to open a .warc file#
A .warc file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts WARC into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Windows | Webrecorder ReplayWeb.page, warcio (command line) |
| macOS | Webrecorder ReplayWeb.page, warcio (command line) |
| Linux | Webrecorder ReplayWeb.page, warcio (command line) |
| Web | FileFlip, ReplayWeb.page |
WARC questions people ask#
What does a WARC file actually store?
A WARC file stores a sequence of records, each one a full HTTP request or response exactly as it crossed the wire, headers and all, along with metadata like the crawl timestamp. That is different from saving a webpage's files directly, because a WARC also preserves how the server responded, including redirects, status codes and content negotiation.
How do I open a WARC file?
A WARC file needs archive-replay software rather than a browser, since it is a log of HTTP traffic rather than a folder of pages. Webrecorder's ReplayWeb.page opens one in a browser tab and replays the captured site as if it were live, and the warcio command-line tool can inspect or extract individual records.
Why does the Internet Archive use WARC instead of just saving web pages?
WARC preserves the complete HTTP exchange the Internet Archive's crawlers captured, not just the final rendered page, which is what lets the Wayback Machine show accurate status codes, redirects and content-type headers years later. Saving files alone would lose that protocol-level context.
Is WARC an official standard?
Yes. WARC was standardized by the International Organization for Standardization as ISO 28500, developed through the International Internet Preservation Consortium, and it is the format essentially every serious web crawler and archive now writes.
Converting WARC files#
Convert WARC to another format
FileFlip does not write .warc files, so nothing on the site converts into this format. It works as a source only.
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.