The engine room

How Shadowin actually works

Shadowin is built on one simple loop: you hear a native-quality sentence, you say it back out loud, and a real speech engine grades how close you got — word by word, in color. No vague stars, no black box. This page opens the hood and shows you exactly what every part of the system is doing, so you can practice with intent and squeeze the most out of every minute.

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Core mechanics

The four-step shadowing loop

Every attempt runs the same path. It takes a couple of seconds, and the same engine powers your very first onboarding baseline and every lesson after it.

01
Listen
Hear the line at native pace, as many times as you like. Shadowing is about matching rhythm, not just words.
02
Record
Say it back. Your audio is captured in the browser and sent securely to the scoring service — never stored beyond the moment it is graded.
03
Transcribe & align
OpenAI Whisper turns your audio into exact text, then our diffing engine aligns it against the target, word for word.
04
See it in color
Each word lights up green, amber, or red, with a single accuracy score from 0–100. You know instantly what to fix.

Reading your results

What the colors mean

The diffing engine grades every word into one of three states, plus a fourth marker for anything extra you said. This is the heart of the feedback — learn to read it and you will improve twice as fast.

Green — spot on

The word matched the target. Clean pronunciation, right word, right place. Example: The future is

Amber — so close

A near-miss: the right word but a slipped ending or a tiny sound difference. It counts as half-credit, not a full miss — the engine knows walks is a near-hit for walk, not a totally wrong word.

Red — missed

A target word that didn’t come through — wrong word, dropped, or unintelligible. These are the words worth looping a few times before you retry.

Red +word — extra

Something you said that wasn’t in the script, shown with a leading +. Stray ums and filler get flagged here so you can see them — but they don’t drag down your core score.

Under the hood

The grading engine, demystified

A pronunciation grader is only as good as how honestly it listens. We made deliberate engineering choices so your score reflects how you really spoke — never inflated, never unfairly harsh.

It transcribes you literally

Whisper is locked to English and runs at zero temperature, which turns off its habit of “creatively guessing” clean words out of mush. We deliberately never feed it the lesson text, so it can’t silently “fix” a dropped ending — if you said walk instead of walks, you’ll see it.

Mumbling can't game it

Whisper reports how confident it was for each stretch of audio. If the recording is too muddy to be sure, a confidence gate caps the result so a mumbled take can’t sneak a perfect score. Speak clearly and you get full marks; mumble and the ceiling drops.

Mistakes weigh more than wins

The score isn’t a flat percentage of correct words. A sharpness curve makes errors bite a little harder, so an almost-perfect read and a sloppy one feel genuinely different — and the jump from 85 to 95 is something you earn.

Near-misses get half credit

When a word is close — the right word with a small slip — it’s scored amber at half the penalty of a full miss, instead of being thrown out as wrong. Real progress shows up as words turning amber before they turn green.

Things we refuse to penalize you for

Before comparing, both texts pass through smart normalization, so harmless variations always count as a perfect match.

Contractions

“do not” = “don’t”. Say it either way.

Numbers

“30” = “thirty” (up to ninety-nine).

Currency

“$30” reads as “thirty dollars”.

Compounds & hyphens

“lifecycles” = “life cycles” = “life-cycles”; “setup” = “set up”.

Smart quotes

Curly and straight apostrophes are treated the same.

Name variants

Common spellings of the same name are clustered together.

Lesson tiers

Three tiers, drawn by word count

Every lesson is sorted into one of three tiers — and the tier is decided by a hard rule: the number of words in the sentence. The badge you see always matches the filter you picked, with zero AI guesswork.

A1–B1

Standard

5–10 words

Single, natural sentences in everyday conversational English. Concrete and practical — the things real people say out loud every day. The place to build clean fundamentals.

B2–C1

Advanced

11–18 words

Richer, multi-clause lines in a confident professional and social register. Natural idioms and real, specific points — never stiff or academic. Where fluency starts to feel effortless.

C1–C2

Executive Masterclass

19–35 words

Long, idea-dense sentences at native pace, written in the cadence of a sharp boardroom or a long-form intellectual podcast. No robotic textbook phrasing — just elite spoken English.

Why word count, not vibes? The tier badge and the library filter are bound to the same measurement at the moment a lesson is created. That means an “Advanced” lesson can never quietly show up under the “Standard” filter — what you filter for is exactly what you get.

Grading modes

Set the bar: Light, Medium, Hard, Hell

The same lesson, four levels of strictness. Your chosen mode sets the accuracy you must hit before an attempt earns XP and counts toward progress. Push the bar up as you grow.

Light

Forgiving and beginner-friendly. Great for warming up or drilling a tough new line without pressure.

Medium

The default. A solid, honest standard for steady daily practice.

Hard

Strict. The bar climbs, and a single mismatched word denies XP — perfect word alignment required.

Hell

Premium. The highest bar plus the same zero-mistake gate. Flawless reads only — the true mastery test.

The zero-mistake gate. In Hard and Hell, a high overall score isn’t enough. Even one red word — a single botched suffix on an otherwise great sentence — blocks the XP for that attempt. It’s the difference between “mostly right” and “native-clean.”

Beyond the number

Your four mastery dimensions

One score tells you how close you were. The mastery breakdown tells you why — four angles on the same attempt, each computed from your word-level alignment so two reads with the same score can still look completely different.

Cadence

Rewards long, unbroken runs of correct words — your rhythm and flow.

Accent

Drops when misses are scattered across the line (drift) rather than clustered in one spot.

Phrasing

Penalizes your single longest stumble — one tripped phrase reads differently from a few stray slips.

Dynamic range

A composite of flow and consistency that rewards expressive, confident delivery.

The AI Coach nudge

After each attempt, Shadowin finds your weakest of the four dimensions and hands you one specific, actionable cue — slow down and exaggerate your vowels, loop a rough patch in your head before retrying, vary your intensity. Small, targeted, and different depending on what tripped you up.

Prefer a calmer screen? Minimalist Mode in Settings hides this breakdown and shows just your score and word colors.

Personalization

How your daily practice is built

Shadowin doesn’t hand everyone the same feed. The lessons you see are shaped by what you choose, what you struggle with, and what you’re due to review — combined by a queue that always has a reason for every pick.

You choose your priority topics

In Settings and on your Dashboard you pick the domains you care about — Business, Tech & AI, Philosophy, Finance, Longevity, and more. Those choices float matching lessons to the top of your library stream and feed straight into your daily focus.

Today's Focus picks up to five

Each day a short, intentional set is assembled in priority order — so the most valuable practice always comes first.

The order Today’s Focus fills its slots

1
Due for review
Lessons your spaced-repetition schedule says are ripe today — caught right before you’d forget them.
2
Your weak words
Fresh lines that target the exact words you’ve missed most often, so practice attacks your real gaps.
3
Your priority topics
Lessons in the domains you said matter to you.
4
Something new
Freshly generated material to keep the feed moving and your ear challenged.

Spaced repetition: your score sets the calendar

The better you do, the longer until you see a line again. Nail it perfectly and it graduates for good.

Below 55

Again today

55–84

In 3 days

85–99

In 10 days

100

Mastered — retired

Behind the scenes, the recommender weights what to surface next: due reviews rank highest, then lessons you’re struggling with (under 70%), then brand-new material — picked with a touch of randomness so you never get the same line twice in a row.

Staying in the game

XP, levels, streaks & your daily window

The systems that keep momentum honest — generous enough to reward real practice, structured enough that progress means something.

XP & levels

Clear your mode’s bar and bank XP. Levels follow a rising curve — the early ones come fast, then each one asks a little more, so a high level genuinely reflects the work behind it. Premium earns XP 1.5× faster.

Streaks

Practice on consecutive days and your streak climbs. Miss a day and it resets to one — counted in UTC so it’s consistent across every device you use.

Free daily window

Free accounts get 10 minutes of regular practice per day, enforced on the server. Premium removes the cap entirely for unlimited daily reps.

Focus Sessions

Result-based sessions built around your weak words — and exempt from the 10-minute window, so you can always get a targeted rep in.

Your voice, your data

What happens to your recordings

Your audio is sent to OpenAI only to produce a transcription, and raw voice recordings aren’t kept on our servers beyond the moment they’re scored. Under OpenAI’s API terms, your inputs are not used to train their models. We store only the non-identifying results that power your progress — your scores, your most-missed words, your streak. Full details live in our Privacy Policy.

Now you know the machine. Go feed it your voice.

Every word you read out loud sharpens the same engine that grades you. Pick a topic, hit record, and watch the colors turn green.

Open the library

Want something specific? Ask for it.

Missing a topic, a word you keep tripping on, or an idiom you want to nail? Tell us and we’ll add real practice material for it.

Want Andrii to personally add your favorite topics, words, or phrases? Sign in to submit a request!

Listen

Record

Transcribe & align

See it in color