Intro
OPML (Outline Processor Markup Language) is a lightweight XML format that aggregates lists of feeds or outlines for newsreaders and productivity tools. It lets users import, export, and sync subscription feeds in a single text file.
This guide breaks down OPML’s structure, practical uses, common pitfalls, and how it compares to other feed‑management standards so you can decide if it fits your workflow today.
Key Takeaways
- OPML is an XML‑based outline format, not a feed itself, and it works with most RSS/Atom readers.
- A single OPML file can contain dozens or hundreds of feed references, making bulk management simple.
- Because OPML is plain text, you can edit it in any text editor or generate it programmatically.
- Security risks arise from maliciously crafted OPML files that can trigger parser vulnerabilities.
- OPML vs JSON Feed: OPML is XML‑centric and widely supported; JSON Feed is newer, lighter, and JSON‑based.
What is OPML?
OPML stands for Outline Processor Markup Language. It was created by Dave Winer in 2000 as a way to share outlines of RSS feeds between applications. According to Wikipedia, the format uses nested XML elements called <outline> to represent each feed or category.
An OPML file always starts with an <?xml?> declaration and contains two main sections: a <head> for metadata (title, dateCreated) and a <body> that holds the actual feed outlines. This hierarchical structure allows you to group feeds into folders, each represented by a parent <outline> with child outlines for individual URLs.
Because it is plain text, OPML works across platforms and can be version‑controlled like source code, a feature many developers appreciate.
Why OPML Matters
In a world flooded with content, OPML provides a universal way to manage subscription lists without vendor lock‑in. W3C’s OPML note highlights that the format reduces the friction of moving feeds between different services.
For teams, OPML acts as a single source of truth for curated news streams, enabling quick onboarding of new members to a shared feed library. It also simplifies backup: you can store a single OPML file containing all your sources.
Furthermore, OPML supports the xmlUrl and htmlUrl attributes, letting readers display both the raw feed link and the associated website, improving user experience.
How OPML Works
OPML operates as a tree of XML nodes. The top‑level <opml> element contains a single <head> and one <body>. Each <outline> can have attributes such as text, type, xmlUrl, htmlUrl, and title.
Here is a minimal OPML skeleton:
<?xml version="1.0" encoding="UTF-8"?>
<opml version="2.0">
<head>
<title>My Feed List</title>
<dateCreated>2025-10-01T12:00:00Z</dateCreated>
</head>
<body>
<outline text="Tech News" title="Tech News">
<outline text="Wired" type="rss" xmlUrl="https://www.wired.com/feed/rss" htmlUrl="https://www.wired.com"/>
<outline text="The Verge" type="rss" xmlUrl="https://www.theverge.com/rss/index.xml" htmlUrl="https://www.theverge.com"/>
</outline>
</body>
</opml>
When a reader parses this file, it builds a data structure like:
- Root: OPML (version 2.0)
- Head → metadata
- Body → list of outline nodes
- Each outline node may contain child outlines, forming a folder hierarchy.
Readers then fetch the xmlUrl resources, merging them into a unified stream for the user.
Used in Practice
Many RSS readers, such as Feedly, Inoreader, and NewsBlur, let you import an OPML file to populate your subscription list in seconds. Export functions produce an OPML file that you can share with colleagues or import into another service.
In content‑curation pipelines, developers generate OPML dynamically from databases of topics, then serve it as a static file that feed‑aggregator bots consume nightly.
Podcast directories sometimes use OPML as a bulk‑upload format for series feeds, allowing creators to submit multiple shows at once.
Risks / Limitations
Because OPML files are XML, they can embed external entities that may cause parser vulnerabilities. Investopedia warns that malicious OPML can exploit XXE (XML External Entity) attacks if a reader does not disable external entity processing.
Another limitation is that OPML only stores references to feeds, not the feed content itself. If a feed URL changes or disappears, the OPML link becomes stale.
Versioning is also an issue: OPML 1.0 and 2.0 differ slightly in attribute handling, which can lead to compatibility problems between older and newer readers.
OPML vs JSON Feed
While OPML is XML‑based and focuses on outlining feed lists, JSON Feed is a JSON‑based format that describes a single feed’s items directly. JSON Feed aims for a simpler, more modern data structure, whereas OPML remains a meta‑format for managing multiple feeds.
In practice, OPML excels at bulk feed management; JSON Feed excels at delivering feed content with less parsing overhead. Some platforms support both: you may export OPML for subscription lists and use JSON Feed for delivering feed items.
What to Watch
As feed standards evolve, watch for emerging specifications like Atom and newer syndication formats that may influence OPML’s future role.
Security updates in popular RSS readers will determine whether OPML remains safe for bulk imports. Always validate OPML files against a schema and disable external entity expansion.
Finally, monitor community adoption: if major platforms deprecate OPML support, you may need to migrate to alternative formats like OPFS (Outline Processing File Standard) or JSON Feed.
FAQ
1. Can I edit an OPML file manually?
Yes. Because OPML is plain XML, you can open it in any text editor, add or remove <outline> elements, and save the file.
2. How do I import an OPML file into Feedly?
Log into Feedly, click the gear icon, choose “OPML Import,” upload your file, and Feedly will add all listed feeds to your board.
3. Is OPML limited to RSS feeds?
No. OPML can outline any type of link, including podcasts, Atom feeds, and even static web pages, as long as you set the appropriate type attribute.
4. What does the type="rss" attribute do?
The type attribute tells the reader which protocol to expect. Common values are rss, atom, and link for generic URLs.
5. Are there size limits for an OPML file?
Most readers can handle files with thousands of outlines, but performance may degrade beyond a few megabytes. For large sets, split the OPML into multiple files.
6. How can I protect my OPML from malicious attacks?
Use a reader that disables external entity processing, validate the file against an XML schema, and avoid opening OPML files from untrusted sources.
7. Can I convert my OPML to JSON Feed?
Yes. Several online converters map the xmlUrl to JSON Feed’s feed_url field, though you’ll still need a separate JSON Feed for each source.
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