What is the ATOM file format?
An .atom file is an Atom Syndication Feed, an open-standard XML document format for publishing frequently updated web content such as blog posts, news articles, and podcasts. The format is defined by IETF RFC 4287, published in December 2005.
An .atom file is plain XML rooted at <feed xmlns="http://www.w3.org/2005/Atom">. The document contains feed-level metadata (id, title, updated, author, link) followed by <entry> elements. Each entry carries its own id, title, published, updated, author, optional <summary> (abstract), and optional <content> (full body). All date/time fields use RFC 3339 format (a subset of ISO 8601). The registered MIME type is application/atom+xml.
Atom was designed as a technically cleaner alternative to RSS, resolving long-standing ambiguities around content types, date formats, and character encoding. Key distinctions: every Atom entry requires a globally unique <id> URI, and Atom clearly separates <summary> from <content>, whereas RSS conflates both in <description>. Despite these advantages, RSS 2.0 remains more widely deployed in practice; all modern feed readers support both formats.
Platforms that expose Atom endpoints include GitHub (repository and release activity), YouTube (channel uploads), Blogger, and GitLab. The .atom extension is less common than .xml for on-disk feed files; most Atom feeds are served directly as HTTP responses. The Atom Publishing Protocol (AtomPub, RFC 5023, 2007) extended Atom for HTTP-based content creation but has largely been superseded by REST APIs.
Security & safety
RISK: LOWAn Atom file is a passive XML document - it cannot execute code. Entry content may contain HTML markup (type="html" or type="xhtml") that could carry XSS payloads if rendered unescaped by a vulnerable reader. Well-maintained feed readers sanitize HTML. External <link> and <content src="..."> elements point to URLs that carry their own risks. Never auto-execute enclosures from untrusted feeds.
Format details
in a nutshell- Atom text editor project file - GitHub's Atom text editor (discontinued December 2022) used .atom files for package configuration (CoffeeScript/JSON-based, unrelated to the syndication format).
Programs that open ATOM files
Windows4 apps
Mozilla Thunderbird
Open-source File > Subscribe to this Feed, paste the Atom feed URL. Thunderbird reads RSS and Atom natively. 
Feedly (web app)
Freemium Add a new feed by pasting the .atom feed URL into the Feedly 'Add Content' search bar.
Notepad++ (XML/text view)
Open-source Open .atom file to inspect or edit raw XML; use Plugins > XML Tools for pretty-print. 
macOS3 apps
Safari
Built-in Safari can display Atom feeds as a formatted list but removed built-in feed subscription in macOS Ventura (2022). Now shows raw XML or a basic list view. 
NetNewsWire
Open-source File > New Feed, paste the Atom feed URL. Open-source, free, actively maintained. 
Linux2 apps
Android2 apps
Technical details
deep spec| Encoding | Text, UTF-8 (default per RFC 4287; other encodings declared in XML prolog) |
| Container | Plain XML |
| MIME type | application/atom+xml |
| Root element | <feed xmlns="http://www.w3.org/2005/Atom"> |
| Date format | RFC 3339 (ISO 8601 subset) - required for all date/time fields |
| Required entry fields | id (unique IRI), title, updated |
| Entry identifier | <id> must be a globally unique IRI per entry (distinguishes Atom from RSS) |
| Content elements | <summary> (abstract) and <content> (full body) are separate elements |
| Typical file size | 5 KB - 300 KB |
| Compression | None on disk; commonly served gzip-compressed over HTTP |
| Older draft | Atom 0.3 (pre-RFC, used <feed version='0.3'>) - now obsolete |
| Related protocol | Atom Publishing Protocol (AtomPub), RFC 5023 (2007) |
| Released | December 2005 (RFC 4287 published) |
| Latest version | Atom 1.0 (RFC 4287, December 2005) - no subsequent revision |
| Open standard | Yes · royalty-free |
| Specification | www.rfc-editor.org |
ATOM conversions
Community Q&A
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