Comma — on-device punctuation and capitalisation for Kotlin Multiplatform

Why Comma

Readable text, without the cloud

No server, no API key, no per-request bill. A small Kotlin library that you can read, test and ship.

Made for Indian text

Hinglish and Tanglish chat, and Hindi, Bengali, Marathi, Gujarati, Punjabi, Tamil, Telugu, Kannada, Malayalam and Urdu in their own scripts, plus English and six European languages.

The right marks

A full stop is । in Hindi, Marathi, Bengali and Punjabi and ۔ in Urdu, where questions end in ؟. Capitals for sentence starts, names and acronyms like NASA.

No dependencies

Pure Kotlin inference. There is no ONNX Runtime, TFLite, ML Kit or native code, and it runs on Android (minSdk 21), iOS, macOS, JVM desktop, JavaScript and WebAssembly, from Kotlin or Java.

Private & offline

The model ships inside the library on every platform. It makes no network calls, needs no permissions and sends no telemetry, so what people dictate never leaves the phone.

~10ms

Per message

Android emulator, once warm

~8MB

On-device

model + tokenizer

Languages

plus Hinglish and Tanglish

Dependencies

no native code

On device

Type it plain, read it right

Real output from the sample app on an Android emulator. These are not mockups.

English

"Can you pick up the kids at 5? I am stuck in a meeting."

Hindi

"आप कैसे हैं? मैं ठीक हूँ।"

Hinglish

"Kal milte hain, OK, bye. Take care."

Same library on every platform

The Kotlin Multiplatform sample app, built from the published artifacts, gives the same result on Android, iOS, desktop and the web.

Android

Hi, Rahul. Are you free tomorrow? I need help with the report.

iOS

Hi, Rahul. Are you free tomorrow? I need help with the report.

Desktop (JVM)

Hi, Rahul. Are you free tomorrow? I need help with the report.

Web (Wasm)

Hi, Rahul. Are you free tomorrow? I need help with the report.

Install

Add it to your build

One line in your Gradle file, from Maven Central. Works in commonMain for Android, iOS, macOS, JVM desktop, JavaScript and WebAssembly. No API key, no account.

Maven Central live

// build.gradle.kts: commonMain, or any platform source set
dependencies {
    implementation("io.github.rajumark:comma:2.0.0")
}

// Gradle picks the right artifact per platform:
// comma-android · comma-jvm · comma-iosarm64 · comma-iossimulatorarm64
// comma-macosarm64 · comma-js · comma-wasm-js

Build with a prompt

Add Comma from rajumark to this Kotlin Multiplatform or Android project.

What it does: on-device punctuation and capitalisation. Given unpunctuated or voice-typed text, it adds commas, full stops, question marks, exclamation marks and capitals. English, Hinglish, Hindi and other Indian languages. ~8 MB, no dependencies, no network.

Install (Maven Central, no extra repository):
  build.gradle.kts (commonMain or any source set): implementation("io.github.rajumark:comma:2.0.0")
  Platforms: Android, iOS, macOS, JVM desktop, JavaScript, WebAssembly

Usage:
  val comma = Comma()            // off the main thread, keep one instance
  val text = comma.restore(transcript)  // "Can you pick up the kids at 5? I am stuck in a meeting."

Repo: https://github.com/rajumark/comma#readme
Add the dependency, then follow the README for the exact API and current version.

Usage

One call per message

Load once and reuse the instance. restore() is thread-safe.

Kotlin

val comma = Comma()

comma.restore("where are you we are all waiting outside")
// "Where are you? We are all waiting outside."

comma.restore("آپ کیسے ہیں میں ٹھیک ہوں")
// "آپ کیسے ہیں؟ میں ٹھیک ہوں۔"

comma.close()

Java

try (Comma comma = new Comma()) {
    String text = comma.restore(
        "can you pick up the kids at 5 i am stuck in a meeting");
}

Use cases

Where Comma fits

Anywhere text arrives without punctuation.

Voice typing & dictation

Clean up speech-to-text output before it goes into a message, note or form.

"where are you we are all waiting outside" → Where are you? We are all waiting outside.

Voice notes & transcripts

Turn a long transcript into readable sentences; long text is handled in overlapping windows.

a 2-minute voice note → paragraphs with full stops

Chat & captions

Tidy fast-typed messages or live captions for display, search or reading aloud.

"आप कैसे हैं मैं ठीक हूँ" → आप कैसे हैं? मैं ठीक हूँ।

Before other text models

Sentence boundaries and capitals help translation, summarisation and text-to-speech downstream.

split into sentences → speak each one

App ideas

20 apps you could build with Comma

Real problems Comma solves today. Pick one and ship it.

Voice typing keyboard · Punctuate dictated text before it lands in the text box.

Voice notes app · Turn a long rambling voice note into readable sentences.

Live captions · Add full stops and capitals to live captions so they are easy to follow.

Dictate emails · Speak an email and send it properly punctuated, no manual fixing.

Meeting minutes · Clean meeting transcripts into sentences before summarising them.

Doctor dictation · Clinical notes dictated in Hinglish, punctuated privately on the phone.

Voice journal · Speak your diary every night and read it back as clean paragraphs.

Lecture recorder · Students get readable lecture transcripts, even offline in class.

Better translation · Split text into sentences first so translation stops mangling run-on speech.

Natural text-to-speech · Real commas and full stops give TTS voices proper pauses.

Clean input for LLMs · Punctuate speech-to-text before sending it to a summariser or chatbot.

Subtitle generator · Break speech-to-text output into proper subtitle sentences.

Call transcripts · Make support-call transcripts readable for review and QA.

Driving mode messages · Dictate a message hands-free and send it with correct punctuation.

Voice-first accessibility · People who can't type send messages that read like typed ones.

Field data collection · Field workers dictate reports in Hindi or Telugu and get clean text.

Complaint & FIR apps · Citizens dictate complaints in their own language, saved as clean sentences.

Chat "tidy up" button · Fix fast lowercase messages with one tap before sending.

Podcast show notes · Turn raw episode transcripts into readable notes and quotes.

Search indexing · Split transcripts into sentences so search can show exact matching lines.

Quality

Honest numbers

Word-level F1 for the four marks (punctuation) and for capitalised words (capitals), on held-out test sets never used for training and on 70 hand-written messages in 15 languages.

	Comma	XLM-R punctuation + true-case (47 languages)	XLM-R base, punctuation only
Hinglish chat, punctuation / capitals	0.83 / 0.92	0.49 / 0.70	0.41 / —
English chat, punctuation / capitals	0.86 / 0.96	0.72 / 0.91	0.75 / —
Hand-written messages, punctuation / capitals	0.74 / 0.89	0.70 / 0.75	0.69 / —
Hand-written messages fully right	43%	26%	—
Formal text, 18 languages, punctuation / capitals	0.65 / 0.79	0.76 / 0.66	0.73 / —
Size	7.8 MB	1.1 GB	1.1 GB
Latency, one message, 1 CPU thread (laptop)	~0.3 ms	~39 ms	~22 ms

Comma is clearly better on chat and messages and capitalises better everywhere, at about 1/140 of the size. On long formal text (news, encyclopedia prose) the much larger XLM-R models place commas better. "!" vs "." is a judgement call it sometimes makes differently.

Reference

API at a glance

Member	Description
`Comma()`	Loads the bundled model. Implements `AutoCloseable`.
`restore(text)`	Returns the text with punctuation and capitals restored. Existing punctuation is replaced; blank text returns `""`.

Pricing & license

Free until you're big.

No API key, no sign-up, no license file. Add Comma to your project and ship. It stays free until your product passes 10,000 monthly active devices, and there's never a limit on how often each device runs it.

Start here

Community

Free

For indie developers, startups and growing apps, up to 10,000 monthly active devices.

Commercial use allowed
No API key, account or license file
Unlimited calls on every device
Runs fully on-device, with no tracking or phoning home

Get started

Commercial

Let's talk

For products above 10,000 monthly active devices on any platform.

One license per product, per model
Pricing that fits your scale
Direct support from the people who built it
Early access to model updates

Email WhatsApp Call

Custom models

Built for you

A small, fast on-device model trained for your language, domain or task.

Punctuation, moderation, classification, replies and more
Tuned on your use case and your users' languages
Shipped as a plain Kotlin library, like Comma
Private: your model runs on your users' devices

Email WhatsApp Call

How devices are counted

A monthly active device is a phone, tablet or other device that runs Comma at least once in a calendar month.

The 10,000 limit applies separately to each product, each platform (Android, iOS, web…) and each Hoverfly model. Crossed it? You have 30 days to get a commercial license.

What the license does not allow

Selling or redistributing Comma or its model on its own, or inside another SDK
Extracting, modifying or fine-tuning the model weights
Using the model or its outputs to train or distill another model
Reverse engineering the model or its file format
Offering it as a hosted API for others

Questions about licensing? Email raju348636@gmail.com or call / WhatsApp +91 63533 21951. Full terms: Hoverfly Community License.

FAQ

Questions

What is Comma?

A Kotlin Multiplatform library (Android, iOS, macOS, JVM desktop, JavaScript, WebAssembly) that adds punctuation and capitals to text that has none, like voice typing, speech-to-text output or fast-typed chat.

Which languages does it support?

English, Hinglish and Tanglish, Hindi, Bengali, Marathi, Gujarati, Punjabi, Tamil, Telugu, Kannada, Malayalam and Urdu, plus Spanish, French, German, Portuguese, Italian, Russian and Indonesian. Chinese, Japanese and Thai are not supported, because they don't put spaces between words. To detect the language first, use Beacon.

What if my text already has some punctuation?

Comma removes the marks it predicts (commas, full stops, question and exclamation marks) and adds its own, and re-cases the text. Other characters like apostrophes, numbers, emails and links are kept.

How long can the text be?

Any length. Long text is cut into overlapping windows, so every word is judged with context on both sides.

Does it run on device?

Yes. Inference runs entirely on the device in plain Kotlin. It makes no server calls, needs no network permission and sends no telemetry.

Is the Kotlin port exact?

Token ids, every word's label and the restored text match the reference implementation on all 94 test vectors, both on the JVM and on an Android device.

How much does Comma cost?

Nothing for products with up to 10,000 monthly active devices per platform, including commercial apps. There is no API key or account, and no limit on how often it runs. Above that, a commercial license is needed; see Pricing.

Can you build a model for my app?

Yes. Hoverfly trains custom on-device models for your language, domain or task and ships them as a small library like this one. Email raju348636@gmail.com or call / WhatsApp +91 63533 21951.

Voice-typed text,
ready to read.

Try the real model, right here

Readable text, without the cloud

Made for Indian text

The right marks

No dependencies

Private & offline

Type it plain, read it right

English

Hindi

Hinglish

Same library on every platform

Android

iOS

Desktop (JVM)

Web (Wasm)

Add it to your build

One call per message

Where Comma fits

Voice typing & dictation

Voice notes & transcripts

Chat & captions

Before other text models

20 apps you could build with Comma

Honest numbers

API at a glance

Free until you're big.

How devices are counted

What the license does not allow

Questions

What is Comma?

Which languages does it support?

What if my text already has some punctuation?

How long can the text be?

Does it run on device?

Is the Kotlin port exact?

How much does Comma cost?

Can you build a model for my app?

Comma is one of eight.