CastReader

Read it aloud. Then have it explained like a teacher.

CastReader keeps you anchored to the original while it speaks, highlights, circles, and explains difficult passages. Choose Overview, Standard, or Deep for the amount of guidance you need.

Add to ChromeGet the iOS or Android app

Free to start · 9 supported languages · Web, PDF, DOCX, EPUB, image, and text workflows

elpais.com
Explaining
Español→English

El interés compuesto significa que los intereses que ganas también generan más intereses con el tiempo. Este efecto bola de nieve convierte pequeños ahorros en una gran fortuna.

Thecoreconceptonthispage:compoundinterest.

1/31.0×

A page in a language you barely read, explained in yours — with the key points marked right on the original. That is Quickread.

Cross-language8

Reading a page in another language? Quickread explains it in the language you know — same pen, same mark-up.

English中文日本語EspañolFrançaisPortuguês8 supported languages

Guided Read-and-Explain

An explanation layer that stays connected to the source

A detached summary tells you what an AI thinks matters. Guided Read-and-Explain walks through the source itself: spoken explanation, synchronized subtitles, and pen-style marks remain tied to the words on the page. That makes it useful when understanding matters as much as finishing.

Inputs
URL, PDF, DOCX, EPUB, image/OCR, and pasted text
Depths
Overview, Standard, and Deep
Guidance
Spoken explanation, synced subtitles, highlighting, circles, and underlines
Best fit
Dense long-form material where the original context must stay visible

Read aloud vs. Read & Explain

Plain TTS pronounces the words. Read & Explain helps you follow what they mean.

Plain read-aloud
What every TTS tool does
  • Reads the original text, word for word
  • Same language as the page
  • Paragraph-level highlight
  • You still have to make sense of it yourself
Read & ExplainCastReader's guided approach
 
  • Explains what the page means, in plain language
  • Your own language — even for foreign pages
  • A pen circles & underlines the exact key points
  • Like a teacher reading along beside you

One source, three levels of guidance

Choose how deeply CastReader should explain

Use Overview to orient yourself, Standard to understand the passage, or Deep to examine reasoning, assumptions, and connections. The original text remains the reference at every level.

Example source passage

Compound interest means your savings earn interest, and the accumulated interest can earn interest too. As the balance grows, each later period calculates returns from a larger base.

Illustrative output: Overview

Answer: What is this about, and what should I notice first?

The passage explains why compound interest can accelerate savings growth: returns are calculated not only on the original amount, but also on interest already added to the balance.

  • Main idea
  • Key conclusion
  • Important terms
  • Document structure

Best for: triage, previews, long reading queues, and deciding where to focus

This fixed example demonstrates the difference in explanation depth. Actual output depends on the source, selected passage, language, and available context.

Interactive Read & Explain Lab

See how the same depth changes across six kinds of reading

Choose a real-world scenario and an explanation depth. Each example shows what stays anchored to the source, what the explanation surfaces, and what still needs verification.

Choose the reading task

Source excerpt

Illustrative research result
In the preregistered trial, the intervention group improved by 8%, but the confidence interval included effects close to zero and the six-week follow-up had 18% attrition.

Choose the explanation depth

Guided explanation sample

Separate the effect estimate from the evidence quality

The 8% figure is the observed difference. The confidence interval says plausible effects also include values near zero, so the estimate may be unstable. Attrition means nearly one fifth of participants were unavailable at follow-up, which could bias the long-term comparison.

This workflow surfaces

  • Effect size
  • Confidence interval
  • Attrition bias
  • Short- vs long-term claim

Verify: Compare baseline balance, missing-data handling, and whether the primary outcome matches the registration.

Plan the right explanation for your passage

Paste up to 1,500 characters to choose a scenario and estimate the useful explanation depth. This local planner does not generate or upload an AI explanation.

Runs in this browser. Your passage is not uploaded or indexed.0/1500 characters

The full CastReader experience reads the source aloud, explains it, and points back to the relevant words. Use the app or extension to run the explanation.

Explain the full passage in ChromeGet CastReader for iPhone or Android

Three things at once — like a teacher pointing at the page

Explanation, pen marks, and subtitles, all synced to the audio.

Explains, not just reads

Instead of reading the original sentence by sentence, it summarizes and unpacks the meaning — so dense, technical, or foreign pages finally click.

Marks the key points

A pen moves across the original, circling, underlining, and highlighting exactly what matters. Your eyes follow the moving pen, so you never drift off.

Subtitles you can follow

Every explanation appears as a synced subtitle, word by word, so you read and listen at the same time — dual-channel focus that fights distraction.

Cross-language understanding

Translation replaces the source. CastReader keeps it visible.

Understand unfamiliar-language text in your own language without losing the words, structure, and evidence in front of you.

A literal translation answers what the sentence says. Explain in My Language stays beside the original and adds the context, relationships, and implied meaning you need to follow it. The examples below use short excerpts from public sources so you can compare the two jobs directly.

Choose a reviewed example

Original source

Botchan by Natsume Soseki

親譲りの無鉄砲で小供の時から損ばかりしている。

Explanation anchor: “親譲りの無鉄砲”

Open the public source

Aozora Bunko public-domain text. Short excerpt shown for study and attribution.

Literal translation

Answers: What do these words say?

Because of the recklessness inherited from my parents, I have done nothing but lose out since childhood.

Explain in my language

Answers: What does this mean here, and why?

The narrator opens by blaming an inherited, impulsive temperament for a lifetime of self-inflicted trouble. The line is comic and self-deprecating, but it also carries pride: he recognizes the consequences without presenting caution as the better way to live.

What the explanation adds

  • An inherited temperament frames the narrator
  • The voice is comic and self-deprecating
  • 損 means adverse consequences, not only financial loss
  • The tension between regret and pride matters

This is one reading of a literary opening, not a replacement for the novel or its ambiguity. Check surrounding passages and other translations when wording matters.

Use translation and explanation for different jobs

CastReader is a reading aid, not a certified translation service. Keep translation when exact wording is the deliverable; use source-anchored explanation when understanding is the obstacle.

English中文日本語EspañolFrançaisPortuguêsItalianoहिन्दी

Explanation language can follow your setting. Read-aloud voices and synchronization currently support the languages shown; availability and quality can vary by language, source, and extraction quality.

Your actual needBest workflow
Publish, quote, or submit exact wordingTranslation plus human review
Understand an argument, concept, or passageExplain in My Language
Learn from the source languageOriginal text, highlighting, and explanation together
Make a legal, medical, financial, or safety decisionQualified professional review

How to use Read & Explain

Three steps, no setup.

1

Install the extension

Add CastReader to Chrome or Edge, or use the mobile app for supported reading flows.

2

Open any page

An article, a research paper, a foreign-language site, even your Kindle book.

3

Click Explain

Tap the 🎧 button and choose Explain. Sit back and follow the moving pen.

Six explanation workflows

Different documents need different kinds of teaching

Each workflow keeps the source visible, supports all three explanation depths, and changes emphasis to match the reader's actual task.

Papers and academic reading

“Can you read this paper to me and explain the argument?”

Start with the research question and contribution, then stay anchored to the abstract, methods, results, and limitations while the explanation follows the paper's structure.

Read arXiv papers aloud

Common inputs

URLPDFDOCXImage/OCRText

Recommended depth

Overview for paper triage; Standard for a first full pass; Deep for methods, arguments, and limitations.

What CastReader can help surface

  • Research question and contribution
  • Methods in plain language
  • Claim-to-evidence links
  • Limitations and terms to verify

CastReader can support comprehension, but it does not validate the research or replace the paper, its data, or expert peer review.

Books and long-form reading

“What does this difficult chapter mean without losing the original page?”

Follow characters, concepts, arguments, and recurring themes while the book remains visible. Use a quick orientation or slow down for a difficult paragraph.

Listen to Kindle books on your phone

Common inputs

EPUBPDFURLImage/OCRText

Recommended depth

Overview before a chapter; Standard while reading; Deep for close reading, difficult prose, or conceptual nonfiction.

What CastReader can help surface

  • Chapter orientation
  • Character or concept context
  • Difficult-passage walkthrough
  • Connections to earlier ideas

Explanations may miss literary ambiguity or context outside the available passage. Keep the book as the primary source.

Reports and business documents

“What changed in this report, and which assumptions matter?”

Move from the executive summary into metrics, comparisons, risks, and dependencies without treating every paragraph as equally important.

Send reports and documents to CastReader

Common inputs

PDFDOCXURLImage/OCRText

Recommended depth

Overview for a briefing; Standard for operating context; Deep for assumptions, risk language, and cross-section relationships.

What CastReader can help surface

  • Executive takeaways
  • Metric and period comparisons
  • Risks and dependencies
  • Questions for follow-up

Explanations are not financial advice and do not verify the accuracy, completeness, or future performance described in a report.

Study and exam preparation

“Teach me this section instead of only reading it aloud.”

Turn notes, textbook pages, slides, and readings into a guided review that identifies definitions, processes, relationships, and likely points of confusion.

Text to speech for students

Common inputs

PDFDOCXEPUBImage/OCRURLText

Recommended depth

Overview for revision planning; Standard for learning; Deep for difficult mechanisms, derivations, and exam review.

What CastReader can help surface

  • Learning objectives
  • Concept breakdowns
  • Process and relationship maps
  • Review questions and weak spots

Use explanations as study support. Check formulas, quotations, citations, and course-specific requirements against the assigned material.

Manuals and technical documentation

“Explain this procedure step by step and point to the source.”

Follow prerequisites, terminology, sequences, warnings, and cross-references while preserving the procedure's original order and wording.

Read technical text in VS Code

Common inputs

URLPDFDOCXImage/OCRText

Recommended depth

Standard for routine procedures; Deep for architecture, troubleshooting, safety notes, and interconnected steps.

What CastReader can help surface

  • Prerequisites and terminology
  • Step dependencies
  • Warnings and exceptions
  • Cross-referenced sections

For safety-critical work, follow the official manual and qualified instructions. An AI explanation must not override warnings or procedures.

Designed to support judgment, not replace it

The strongest use of Read & Explain is source-grounded comprehension: hear an explanation, see what it refers to, and verify important details in the original.

  • The original document remains the source of record.
  • AI explanations can be incomplete or mistaken and should be checked.
  • Legal, medical, financial, and safety-critical decisions need qualified review.
  • Output quality depends on extraction quality and the context available to CastReader.

Read & Explain — Questions

What's the difference between Read Aloud and Read & Explain?▾

Read Aloud reads the original text out loud, word for word. Read & Explain instead explains what the page means — in your own language — while a pen marks the key points on the original. One reads it to you; the other teaches it to you.

What language does it explain in?▾

The explanation language can follow your browser or your setting. Read-aloud voices and synchronization currently support English, Chinese, Japanese, Spanish, French, Portuguese, Italian, and Hindi; availability and quality can vary by language and source.

Can it explain a page written in a language I don't read?▾

Yes. For supported language workflows, CastReader can keep the foreign-language source visible while explaining the passage in the language you choose and marking the relevant words. Availability and quality vary by language, source, and text extraction.

Is Explain in My Language the same as translation?▾

No. Translation tries to reproduce the source wording in another language. Explain in My Language keeps the source visible and adds context, relationships, and plain-language meaning. Use reviewed translation when exact wording is the deliverable; use explanation when understanding is the obstacle.

How is this different from an AI summary tool?▾

A summary hands you a block of text. Read & Explain is a guided, spoken walkthrough: it talks you through the page while a pen circles and underlines the exact spots on the original, so you stay anchored to the source instead of trusting a detached summary.

Does it work on Kindle, WeRead, or PDFs?▾

Yes. It works on ordinary web pages and on rendered readers like Kindle Cloud Reader and WeRead — it reads what's on screen, then explains it. On paginated readers it explains the page you're currently on.

Will the pen marks cover the text?▾

No. The pen uses light highlights, underlines, and circles that sit over the original without hiding it — just like marking up a printed page with a highlighter.

Is it free?▾

CastReader is free to start with a daily allowance for read aloud and AI explanations. Pro is available for longer listening, premium voices, faster playback, and more explanations. Current limits are shown on the pricing page.

Which browsers are supported?▾

The browser extension supports Chrome, Edge, and other compatible Chromium-based browsers. CastReader also has iPhone and Android apps; current official download options are listed on the download page.

What are Overview, Standard, and Deep explanation?▾

Overview identifies the main idea, structure, and conclusions. Standard walks through the passage in plain language with definitions and relationships. Deep examines reasoning, assumptions, limitations, and connections that may need verification.

What types of content can CastReader explain?▾

Read & Explain is designed for books, papers, reports, contracts, study materials, manuals, webpages, and AI answers. Supported workflows include URLs, PDFs, DOCX files, EPUBs, images or screenshots through OCR, and pasted text.

Try guided Read & Explain on your next difficult passage

Start with the free daily allowance, then choose Pro when you need longer listening and more explanations.

Add to ChromeAdd to EdgeGet the iOS or Android app

More ways to listen

Listen to Kindle

Turn your Kindle library into audiobooks

Listen to AI chats

A listen button on every ChatGPT & Claude reply

Free TTS online

Paste text, pick a voice, listen instantly

PDF to audiobook

Convert any PDF into natural audio

Reading voice library

Compare real voice samples for papers, books, and long documents

Read & Explain in Your Language, With the Source Visible | CastReader