Build an RSS, Atom, or JSON Feed discovery link tag

This builder takes a supported feed type and an absolute feed URL, selects the matching media type, escapes characters that could break an HTML attribute, and returns a complete link rel alternate element ready for the document head. It supports RSS, Atom, and JSON Feed while rejecting unknown formats and invalid non-web URLs instead of producing misleading markup.

Choose the feed format that matches the published document

A discovery tag is useful only when its type attribute accurately describes the resource at the URL. Select rss for an RSS XML document, atom for an Atom XML document, or json-feed for a JSON Feed document. The builder maps those choices to application/rss+xml, application/atom+xml, and application/feed+json respectively. It does not inspect or download the destination, so the selected format must reflect what your server actually returns. Keeping this declaration accurate helps feed readers decide whether they understand the resource before fetching or parsing it. It also avoids a common copy-and-paste mistake: advertising an Atom endpoint with the RSS media type, or exposing a JSON Feed URL as generic JSON. Unknown names are rejected rather than guessed because a plausible but incorrect type can make discovery harder to debug. If a site offers several formats, run the builder once for each endpoint and place every resulting element in the page head. Each tag then represents one genuine alternate representation that a compatible client can choose.

Provide the canonical public feed URL

Enter an absolute HTTP or HTTPS URL that a visitor's feed reader can reach, such as https://example.com/feed.xml. Absolute URLs are preferable in discovery metadata because copied pages, cached documents, and clients with different base-URL behavior still resolve the same feed endpoint. The builder trims surrounding whitespace, verifies that the value can be parsed as a URL, and rejects schemes such as file, data, or javascript. It preserves the supplied web URL in the result rather than silently rewriting its path, query, fragment, escaping style, or letter case. Characters that have special meaning inside an HTML attribute are encoded in the generated markup, so a query string containing an ampersand becomes safe source without changing the returned URL field. Validation here confirms the shape and scheme, not ownership, availability, content type, redirects, or TLS configuration. Test the published endpoint separately and make sure it returns the intended feed with a successful response. When moving a feed, update both the server redirect and this discovery tag so new subscribers begin with the current canonical address instead of relying permanently on redirection.

Place and verify the generated element

Copy the returned tag into the head of the HTML page whose feed you want clients to discover. The result uses rel="alternate", the standard format-specific media type, and the escaped feed URL as href. It deliberately omits a title because the requested inputs contain only format and URL; adding invented descriptive text would be less useful than letting a publisher choose language and wording in their own template. If your site has multiple feeds, such as a main publication feed and separate topic feeds, create one element per URL and consider adding meaningful titles in your application code where users need to distinguish them. View the delivered page source after deployment, because a template engine or content-security layer may transform markup even when the generated value is correct. Then try discovery with at least one feed reader and inspect the response headers from the feed endpoint. The browser tool and API run the same deterministic function, so identical inputs produce identical fields and markup. Automated builds can call the API for $0.002 per request, while interactive use can run locally in the browser without sending the URL for processing elsewhere.