Listen (TTS)

Readest can read any book out loud. TTS works on every platform, with an option to choose between on-device voices and higher-quality cloud voices. Playback continues in the background with lock-screen controls.

Start TTS

In the reader, tap the headphones icon in the bottom toolbar (tap the middle of the page first if the toolbars are hidden). With a hardware keyboard, the T key toggles it too. Playback starts from the current paragraph and continues through the chapter.

A mini player appears at the bottom of the page with play / pause, previous / next sentence, and stop. Tap the cover or title in the mini player to open the full Read Aloud player, which is where you change the voice, speed, and sleep timer.

Playback controls:

Action	Shortcut
Play / Pause	`Space`
Next sentence	`Ctrl+]` / `Cmd+]`
Previous sentence	`Ctrl+[` / `Cmd+[`
Next paragraph	`Ctrl+Shift+}` / `Cmd+Shift+}`
Previous paragraph	`Ctrl+Shift+{` / `Cmd+Shift+{`

You can also read aloud a selection only — select text in the reader and press Ctrl+R / Cmd+R. Readest reads the selection and stops.

Lock-screen controls and system media keys work on iOS, Android, macOS, and Windows — pause and skip without opening the app.

TTS engines

Readest ships four engines, and you can add your own custom TTS services.

Native (system) TTS — uses the operating system's built-in voices. Fully offline, instant response, on Android and iOS (iOS uses Apple's on-device speech engine). Desktop native voices aren't wired up yet — on macOS, Windows, and Linux, use Edge TTS or the Web Speech voices in the web app.
Web Speech API — browser-based TTS when running in the web app. Depends on what the browser exposes.
Edge TTS — cloud-synthesized neural voices from Microsoft Edge's TTS. High quality, natural-sounding, many languages. Requires a network connection and sends the current sentence to Microsoft's servers for synthesis.
Readest Voice — premium neural voices synthesized in the cloud by Readest, for Plus and Pro subscribers. See Readest Voice.

Edge TTS is the default whenever the device is online — on iOS and Android too. Readest Voice and custom services are never picked automatically; they read only after you choose one of their voices. Readest doesn't switch to the system voices on its own either: pick one from the System TTS group in the voice picker, and Readest remembers that choice per language from then on.

If you'd rather keep everything on-device, pick a voice from the System TTS group.

Voices & languages

Choose a voice. While TTS is playing, open the full Read Aloud player (tap the cover or title in the mini player) and tap Voice. Voices are grouped by engine — your custom TTS services, Readest Voice, Edge TTS cloud voices and, on iOS and Android, System TTS on-device voices — and filtered by the language of the current book. Only one group is open at a time, starting with the group of the voice in use. Picking a voice also switches to its engine, and the choice is remembered per language. Voice and engine selection live here; Settings → TTS covers custom services, highlighting, media info, and the audio cache.

Readest automatically switches voices when a book contains multiple languages, so a bilingual edition uses the right voice for each passage.

To add more voices:

Android — system TTS settings, installed engines (Google TTS, Samsung TTS, etc.).
iOS / iPadOS — the System TTS group lists Apple's on-device voices; download more under iOS Settings → Accessibility → Spoken Content → Voices. Readest picks its own default from that list rather than the voice chosen in iOS settings, so select the one you want once in the voice picker.
macOS / Windows / Linux — no native voices yet; use Edge TTS (cloud) or, in the web app, the browser's Web Speech voices.

Newly installed voices show up in Readest the next time you open the voice picker.

Speed & controls

Speed — 0.5× to 3×, in fine increments. The default is 1×.
Sleep timer — stop at the end of the current chapter or after a duration from 1 minute to 8 hours.
Pause After Each Sentence — the button left of the playback controls in the full Read Aloud player. Once a sentence is read, playback stops on the next one; press play to hear it. Useful for shadowing or dictation practice.
A-B repeat — the button right of the playback controls. Tap it once to mark the sentence being read as the start (A), again to mark the end (B), and a third time to clear. Readest loops the span between them, tinted in the book. Mark the same sentence twice to repeat just that sentence.

Both study modes are hidden while a paired audiobook is playing. Turned on mid-paragraph, they take effect at the next sentence.

Speed changes take effect immediately — mid-sentence if needed.

Readest Voice

Readest Voice is a set of premium read-aloud voices that Readest synthesizes on its own servers. It comes with a subscription only: the one-time Full Customization purchase doesn't include it. Plus unlocks the voices badged Plus, and Pro unlocks both the Plus and Pro voices.

Readest Voice appears in the voice picker for everyone, but voices your plan doesn't include are greyed out. Tap one to open the plans page, or the sign-in page if you aren't signed in.

If Readest Voice has no voice for the book's language, the default engine reads that book instead, and your Readest Voice pick is kept for books it can read.

Custom TTS services

Use your own OpenAI-compatible speech service, such as OpenAI's speech API or a local server like Kokoro. Open Settings → TTS → Custom TTS Services and tap Add TTS Service. This needs Plus, Pro, or the one-time Full Customization unlock; otherwise the row carries a Premium badge and opens the plans page.

For each service, fill in:

Name — the label of its group in the voice picker.
Base URL — Readest sends speech requests to {Base URL}/audio/speech.
API Key — optional for local servers.
Model — the model name the service expects.
Instructions — optional, for models that accept a speaking style.

Tap Test to hear a sample and see how many voices the service offers. Readest reads the voice list from {Base URL}/audio/voices; a service without one gets the standard OpenAI voices. Voices that name a language (Kokoro's af_… or zf_… voices, for example) are offered only for books in that language; the others read any language.

Each enabled service shows up as its own group in the voice picker. Custom voices work with offline audio, and highlight by sentence rather than by word. Services sync to your other devices with the API key encrypted.

Sentence highlighting

While TTS plays, the text being read is highlighted in the book. Settings under TTS → Highlighting let you tune:

Granularity — highlight the whole Sentence, or just the single Word as it's spoken (the default). Word-by-word read-along needs an engine that reports word timings — Edge TTS and the Web Speech voices do; the on-device Native voices highlight by sentence. CJK text also highlights by sentence.
Style — highlight, underline, strikethrough, squiggly or outline.
Color — the highlight color.

Want to keep a line you just heard? Press Shift+M to save the sentence TTS is currently reading as a permanent highlight (using your default highlight style and color) — no need to select it by hand.

In paginated mode, Readest auto-advances the page when the reader crosses the edge of the visible content. In scrolled mode, the view scrolls smoothly to keep the currently-spoken sentence in view.

When the active engine can align audio to text, the expanded Read Aloud player shows a lyric-style transcript centered on the current sentence. Scroll to another sentence and press play to continue from there.

For pronunciation fixes (e.g., making TTS read "LLM" correctly), see Proofread rules — rules can be scoped to TTS-only so they don't touch the visible book text.

Offline audio

With Plus, Pro, or the one-time Full Customization unlock, and a download-capable TTS voice, open the expanded Read Aloud player and choose Offline Audio. Download one chapter or Download all; each row shows whether it is waiting, downloading, partial, failed, or ready offline.

The queue is saved per book, so you can close and reopen the player without losing it. Tap a queued chapter to cancel it, retry a partial or failed chapter, or use Clear all to remove the downloaded speech and reclaim its displayed storage size.

Pair an audiobook

Readest can use a human-narrated audiobook as an ebook's read-along audio:

Open the ebook, then choose Book Menu → Pair Audiobook. Pairing works with EPUB books, including EPUBs synced from Audiobookshelf; PDF, MOBI, and AZW3 books don't offer it.
Select one .m4b file or a set of .mp3 / .m4a tracks in playback order. If you've connected Audiobookshelf, you can choose a title from that server instead and stream it without downloading.
Match one known ebook chapter to its audio chapter or track. Readest maps the remaining chapters sequentially.
Review the mapping, preview any chapter, and leave mismatches unpaired or adjust them manually.

After pairing, the normal Read Aloud player follows the narration with a timeline, 15-second back / 30-second forward controls, and audiobook chapter skips. Return to Book Menu → Manage Audiobook to edit the mapping, replace the audio, or remove the pairing.