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Castella
Castella app icon

Turn what you read into a podcast.

What the app’s empty library says

Add text, a PDF, or an article link. Castella writes a conversation between hosts about it, creates the audio, and puts the episode in your library with a transcript and its sources.

Download on the App Store

iPhone and iPad · iOS 15 or later · Account and internet needed

  1. Castella Create a podcast, Text selected: a pasted paragraph about how stories help us remember ideas

    Add text, a link or a PDF

    Paste text, add up to 5 public article links, or choose a PDF with selectable text (up to 10 MB).

  2. Castella Length options 5 min (selected), 10 min, 20 min and Custom, and the Hosts row “Maya & Theo · Change hosts”

    Pick a length and the hosts

    5, 10 or 20 minutes, or Custom. Choose the hosts, and under Customize the language and the style.

  3. Castella episode “Why We Remember Stories” (Mira, Oscar · Oct 18, 2026 · English) with Offline, back 15, play, forward 15, 1x speed and a 0:00 to 6:00 scrubber

    Listen, and read along

    The episode has a player, the transcript and the sources it was made from.

Screens: Castella in the iPhone 16 simulator (iOS 26), captured 19 October 2026 from the current development build with sample episodes and text, in light and dark mode (this page shows the one that matches your device). Labels can differ slightly from the App Store version, 1.7.6.

Castella library “Your podcasts”: four episodes marked Ready (Why We Remember Stories 6:00, The Science of Better Sleep 7:05, What Makes a City Feel Like Home 8:10, A Short History of Everyday Ideas 9:15) and How Small Habits Last, still “Creating audio”

Castella writes the conversation, then makes the audio

Castella’s server writes a conversation between your hosts about the material you gave it. In the app: “We’re writing your episode. Audio comes next.”

The server turns the conversation into speech. In the app: “We’re creating the audio. Your episode will appear in Library when it’s ready.”

You can leave: “Follow progress in your library once creation starts.”

  • Audio downloads to the iPhone the first time you play it; after that, the episode plays offline.
  • Search the transcript, copy a part, or share the audio with the iOS share sheet (“Save or share audio”).

A transcript and the sources, with every episode

The episode screen has the player (“Back 15 seconds”, “Forward 15 seconds”, “Playback speed”), the Transcript, and the Sources it was made from.

The Sources tab lists the text, links and files behind the episode, with “Open original source” for links.

Castella Sources tab: Text 1 “Your content”, Links 1 https://example.com/story-notes with “Open original source”, and Files 1
Castella transcript: Mira asks why a good story stays with us; Oscar answers that a story gives an idea a place to live

What you need

  • An account. Sign in with Apple, or with email. You need one to create a podcast.
  • A connection. Nothing is generated on the iPhone: your text, links and PDFs go to Castella’s server and its voice providers to make the episode.
  • Credits. Each episode uses credits. The create screen shows your balance and the estimate before you start.

Limits

  • Castella can’t read scanned PDFs without selectable text, or password-protected PDFs.
  • Castella can’t open links that need sign-in, or take more than 5 links.
  • Castella can’t use YouTube, audio, video or image files as a source.
  • Castella can’t make episodes longer than 20 minutes without a plan, or 60 with one.

Which PDFs work

Questions

What does Castella make?
A podcast episode about the text, PDF or article links you add: a conversation between hosts, as audio, with a transcript and the sources it was made from.
Which PDFs work?
PDFs up to 10 MB each with selectable text: up to 3 per podcast, or 10 with an active plan. Scanned and password-protected PDFs don’t work; paste the text instead.
Can I listen offline?
Yes, once an episode is downloaded: the audio downloads the first time you play it. Creating an episode needs an internet connection and an account.
How long can an episode be?
Pick 5, 10 or 20 minutes, or a custom length: up to 20 minutes without a plan, up to 60 with Plus or Pro.
Which languages?
Episodes can be in English, Russian, Spanish, French, German, Japanese or Chinese.
Does my content stay on my iPhone?
No. Castella is online-first: text is sent to Castella’s server, PDFs are uploaded and links are fetched there, and voice providers make the audio. Your library and downloaded episodes are stored on the device.