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Castella
Castella app icon

Turn what you read into a podcast.

Add text, a PDF or an article link. Castella writes a conversation between hosts about it and turns it into audio. The episode shows up in your library with a transcript and its sources.

Download on the App Store

iPhone and iPad · iOS 15 or later · Needs an account and an internet connection

  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 some text, add up to 5 public article links, or pick a PDF with text you can select, 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”

    Choose a length and your hosts

    Pick 5, 10 or 20 minutes, or a custom length. Choose your hosts, then set the language and style under Customize.

  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

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

Screens from Castella’s current development build on an iPhone 16 simulator (iOS 26), 19 October 2026, with sample episodes and text. You see the light or dark version to match your device. Labels may differ slightly in 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”

How an episode gets made

First, Castella’s server writes a conversation between your hosts about what you added.

Then it turns that conversation into speech. The episode appears in your library when it’s ready.

You don’t have to wait on that screen. You can follow its progress in your library.

  • The audio downloads to your device the first time you play it. After that, you can play that episode again without a connection.
  • Search the transcript, copy a part of it, or share the audio from the share sheet.

Read along, and see where it came from

The episode screen has the player, with 15-second skips and playback speed. Below it are the Transcript and the Sources.

Sources lists the text, links and files the episode was made from. For a link, tap “Open original source” to go back to the page.

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 make a podcast.
  • An internet connection. Episodes aren’t made on your device. Your text, links and PDFs go to Castella’s server and its voice providers.
  • Credits. Each episode uses credits. Before you start, the create screen shows your balance and about how many it will use.

What Castella can’t do

  • It can’t read scanned PDFs or PDFs locked with a password.
  • It can’t open pages that need a sign-in, and it takes up to 5 links.
  • It can’t use YouTube, audio, video or image files.
  • Episodes can be up to 20 minutes without a plan, or 60 minutes with one.

Which PDFs work →

Questions

What does Castella make?
A podcast episode about the text, PDF or links you add. Your hosts talk it through, and you get the audio, a transcript and the sources.
Does Castella read my PDF word for word?
No. Castella writes a new script about it, and the host or hosts talk it through rather than reading it out. For a word-for-word reading, use a text-to-speech reader.
Is Castella free?
You need an account; episodes use credits.
Which PDFs work?
PDFs up to 10 MB each, with text you can select. You can add 3 per podcast, or 10 with an active plan. Scanned and password-protected PDFs don’t work, so paste the text instead.
Do I need an internet connection?
Yes, to make an episode, and you need an account too. The audio downloads the first time you play an episode. After that, you can play it again without a connection.
How long can an episode be?
Pick 5, 10 or 20 minutes, or a custom length. Without a plan, episodes can be up to 20 minutes. With Plus or Pro, up to 60.
Which languages can episodes be in?
English, Russian, Spanish, French, German, Japanese or Chinese.
Does my content stay on my iPhone?
No. Castella works online. Your text goes to Castella’s server, PDFs are uploaded there and links are read there, and voice providers make the audio. Your library and downloaded episodes are kept on your device.
Does Castella work on iPad?
Yes. Castella works on iPhone and iPad with iOS 15 or later.
How do credits work?
Making an episode uses credits. Before you start, the create screen shows your balance and about how many credits the episode will use. Plans and one-time top-ups add more.

Guides: How to Turn a PDF into a Podcast on iPhone · all guides