Draft:PortCast


PortCast is an open protocol for moving a podcast listener's data between applications. It defines a JSON-based document format and an optional HTTPS synchronization API that share a single data model, intended to carry a user's podcast subscriptions, listening history, playback position, queue, bookmarks, and per-feed preferences so that changing apps does not mean starting over. The protocol was created by a developer using the handle Trimplayer and is published as a free, openly licensed specification that anyone may implement. As of the 0.2.0 working draft, the specification is being prepared for submission to the RFC Editor under the Independent Submission stream as an Informational document.

Overview

PortCast is described by its editors as a listener-owned, federated format that requires no central server, directory, or account. The protocol builds on identifiers already present in RSS (the item GUID and feed URL) and the Podcast Namespace (podcast:guid) rather than introducing a new identity scheme, and adds a platform-reference identifier of last resort for shows that have no RSS feed, such as platform-exclusive content. The data model covers several categories of listener data:

  • Subscriptions — followed feeds together with tags, identifiers, and follow dates.
  • Episode state — a status for each episode (such as unplayed, in progress, completed, or archived) along with playback position, play count, ratings, and an optional log of playback events.
  • Queue — an ordered "up next" list that persists across applications.
  • Bookmarks and clips — time-stamped notes within an episode, which can be extended into clips with an end timestamp.
  • Preferences — global and per-feed settings such as playback speed, intro and outro skipping, silence trimming, and automatic download policy.
  • Extensions — namespaced data outside the defined model, which consuming applications must preserve on round-trip.

Design goals

The project positions itself as an alternative to existing partial solutions. Its documentation notes that the OPML format transfers subscriptions but little else, while per-application exports from services such as Apple, Spotify, and Pocket Casts use differing and largely private formats. Stated design principles include listener ownership, interoperable identity based on open identifiers, losslessness within the model, support for partial and incremental data, human readability, and explicit versioning. The project is federated by design: each application exposes its own endpoint on its own domain, and the editors state that they will not operate a central service.

Data model and identity

A PortCast document is a single UTF-8 JSON object that declares its protocol version as a SemVer string. Podcasts are matched primarily by podcast:guid, falling back to a feed URL, while episodes are matched by their RSS item GUID, falling back to an enclosure URL; platform-reference URIs are used only when neither open identifier is available. The 0.2.0 draft also defines a "completeness" field and accompanying merge rules, which allow a consumer to combine documents assembled from several upstream sources over time, such as a real-time export and a slower historical export.

Sync API

In addition to the file format, version 0.2.0 specifies an optional API mode in which the same entities are exposed over HTTPS for incremental synchronization. Servers may publish a discovery document, authenticate using OAuth 2.0 or bearer tokens, and support features such as delta sync, pagination, optimistic concurrency, and webhooks. File mode is described as the interoperability floor that every conforming implementation can fall back to.

Specification and tools

The protocol is defined in a specification document and validated by a JSON Schema (draft 2020-12). The specification is published under the Creative Commons Attribution 4.0 license, and the accompanying reference code is released under the MIT License. A reference implementation written in Python provides data models, a schema-driven validator, a bridge between OPML and PortCast, and a command-line interface. A reference exporter for Spotify is also provided as a worked example; according to the project, it does not store user data, and the Spotify access token is held only in a short-lived signed cookie and discarded after the export completes.

History

PortCast was first published as a version 0.1.0 draft on 26 May 2026, defining the file format. Version 0.2.0, dated 29 May 2026, added platform references for shows and episodes without an RSS feed, provenance fields, the completeness field and merge semantics, and a unified version number shared by the file format and the new API mode. The specification and reference code are hosted on GitHub.

See also

Category:Open formats Category:Podcasting Category:JSON

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