The short answer

Hindi splits consonants four ways where English splits them two, along aspiration and along whether the tongue curls back. English speakers hear one sound where Hindi hears four, and produce one where four are needed. Every one of those errors transcribes as the word you meant, so a text-based app finds out nothing. A tutor that receives your audio directly can hear them. Five tutors, from Delhi to Varanasi, and an authored CEFR syllabus behind it.

Hindi is spoken by an enormous number of people and taught, to English speakers, surprisingly badly. Most courses front-load the script and the vocabulary, and leave the thing that actually determines whether you are understood almost untouched.

Four sounds where English has one

The Hindi stop system splits along two axes at once: aspirated against unaspirated, and retroflex against dental. So where English has roughly a t and a d, Hindi has त थ द ध and ट ठ ड ढ, and the differences between them are lexical.

An English speaker hears these as variants of the same sound, which means the first task is not production but perception. You cannot reliably make a distinction you cannot hear.

Why the tutor hearing you is the whole point

Every one of those errors survives transcription. Say the dental त where the retroflex ट belongs and speech recognition, which is built to return the word you probably meant, will usually hand the tutor the correct word anyway. Miss the aspiration on फल and you get फल back.

So an app that transcribes you and passes the text to a model receives a perfectly formed sentence. It will tell you your grammar is good. It has no way of knowing you have been saying a different word this whole time.

Here the audio goes to the model directly and it replies in audio. Nothing transcribes you first, so the tutor can hear what you actually produced, and can say the word back to you properly inside its own reply.

About the script

Hindi is written in Devanagari, and it is worth learning. It is a genuinely well-designed system, more regular than the Latin alphabet, and it takes a couple of weeks.

It is also worth knowing that a great deal of real-world Hindi is written in Latin transliteration, in messages, on social media, in film titles. Romanized Hindi is not a learner’s crutch, it is a normal register of the language, and your Hindi will be perfectly usable if you meet it that way.

The app shows a Latin reading beneath native script by default, and it can be switched off in a moment. If you have decided you want to read Devanagari, turn it off early, because the reading is easier to lean on than to abandon.

What a session is

Unscripted conversation with something you can interrupt, backed by an authored CEFR syllabus of 281 items from A1.1 to C1, of which 102 are capabilities: concrete things you can do rather than grammar points. The pronunciation patterns above are five of twenty authored for Hindi specifically.

The five tutors span the country deliberately. Delhi and Mumbai are the most standard starting points. Lucknow gives you the more formal, courteous register. Varanasi brings eastern colour that will stretch your ear.

Travel

Travel Mode changes the app for the length of a trip: rehearsal before you go, one real-world mission a day while you are there set in the city you are in, and a debrief with your tutor afterwards about how it actually went with a real person.

The five Hindi tutors

Every language has five, each from a different place and each sounding like it. You can switch whenever you like, and the app remembers where you are regardless of who you talk to.

AaravDelhi
Clear, standard Khari Boli Hindi with the urban, slightly clipped delivery of the capital.
PriyaMumbai
Modern urban Hindi spoken with the bright, fast rhythm of the city.
RohanLucknow
Refined, even-paced Hindi with the soft elegance and politeness associated with Awadhi tehzeeb.
MeeraJaipur
Rajasthani-tinged Hindi with a rounded, courtly warmth and an unhurried, melodic lilt.
AnjaliVaranasi
Bhojpuri-tinged eastern Hindi with an earthy, sing-song rhythm and a relaxed, riverside ease.

What English speakers usually find hard

These are drawn from the pronunciation patterns the tutor listens for in Hindi. Because it hears your voice rather than a transcript of it, they are things it can actually notice and work on with you.

Aspiration is meaningful, and English does it by accident: क and ख, प and फ, त and थ differ only in a puff of air, and the difference changes the word: पल is a moment and फल is fruit. English aspirates its initial stops unpredictably and never contrastively, so speakers produce the wrong one about half the time without hearing it.
Retroflex and dental are two whole series: ट ठ ड ढ have the tongue curled back against the roof of the mouth, giving a hard, hollow sound. त थ द ध have the tongue tip against the back of the teeth, softer than an English t or d. English sits between the two and collapses them. टाल and ताल are different words.
Breathy voiced consonants, which English simply lacks: भ घ ध झ are voiced stops released with a murmur. भारत, घर, धन्यवाद. The breathiness happens during the voiced release, so भ is one sound rather than a b followed by an h, which is what most learners produce.
The written vowel that is not said: Every consonant carries an inherent a, and spoken Hindi deletes it in predictable positions, especially at the end of a word. नमक is namak, not namaka. समझ is samajh. Written Hindi has more vowels in it than spoken Hindi does, which is disorienting when you are reading aloud.
Vowel length changes the word: दिन is a day and दीन is quite different. सुख and सूख likewise. English vowel length is not contrastive in this way, so learners tend to produce a middling length that lands on neither.