Kotlin · Android language work

Kotlin App Development Company

Mobulous is a mobile app development company that builds Android apps in Kotlin and extends existing Java codebases without a forced rewrite. We do not sell Kotlin Multiplatform, Jetpack Compose showcases or server-side Kotlin as shipped product lines on this page. 700+ apps delivered, 12+ years, ISO 27001 certified.

700+
Apps delivered
12+
Years · founded 2013
4.7★
Clutch · 103 reviews
Book a discovery call → See the Java migration decision →
500+ clients · 30+ countries
100+ experts
ISO 9001:2015 · ISO/IEC 27001:2022 · CMMI Level 3
4.7/5 Clutch · 103 reviews
What we build in Kotlin

Android work where Kotlin is the language of record

This page is about language-level Android delivery: new modules in Kotlin, mixed Java/Kotlin repositories, and Play Store submission. Platform depth for Android as a whole sits on our Android app development page. Dual Swift and Kotlin product builds sit on native mobile app development.

New Android apps in Kotlin

Greenfield Android clients where new code starts in Kotlin against the Android SDK and the libraries your product needs.

Java codebases extended in Kotlin

New features and modules written in Kotlin beside existing Java. Interop is the rule, not a temporary workaround.

Incremental Java-to-Kotlin conversion

File-by-file conversion where tests and active feature work make it safe. Not a billed full rewrite by default.

Kotlin Android modules inside larger products

Android clients that share APIs with web or iOS surfaces. Stack rows in apps.csv often list Kotlin beside React JS or Node for that reason.

Play Store packaging and release support

Signing, store listing support and release coordination for Android builds after scope is agreed.

Maintenance on mixed Java/Kotlin apps

Ongoing work on repositories that will stay mixed for years. Half-migrated is a normal steady state.

Migration decision

You already have a Java app. How much of it should become Kotlin?

Most Kotlin work is not greenfield. It is an existing Java Android app, and the real question is how much to convert and when. Broader Android platform choices, including Compose depth, stay on Android app development.

Kotlin and Java run side by side in the same project

Nothing forces a full rewrite, and that is the most important fact in this decision.

The cheapest path is new code in Kotlin, existing code untouched

Ship features in Kotlin while Java modules keep working. Interop is what most real engagements need.

Converting a file is not the same as making it idiomatic

An automated conversion compiles and still reads like Java. Idiomatic Kotlin is a separate pass with reviews and tests.

Null safety only helps where the boundary is annotated

Java code calling Kotlin can still pass null into something that does not expect it. Platform types remain a risk until annotations and wrappers catch up.

Converting a class with heavy test coverage is low risk

Converting one without tests is a rewrite pretending to be a migration.

Libraries written in Java work unchanged

There is no dependency forcing function that requires Kotlin everywhere before you ship.

A half-migrated codebase is a normal steady state, not a failure

Many production apps stay mixed for years while feature work drives conversion.

When wholesale conversion is worth doing

A small codebase, a team already fluent in Kotlin, or a rewrite already planned for other reasons.

When wholesale conversion is not worth doing

A large legacy app with thin tests, no Kotlin experience on the team, and no feature work driving the change.

The honest answer for most teams is incremental conversion, driven by whichever files they are already touching. An agency that proposes a full conversion as a project should be asked what it buys beyond a language label.
What Kotlin changes in delivery

Language features that change how Android work ships

New Android projects default to Kotlin because Google standardised on it and the tooling assumes it. That does not make Kotlin cross-platform, and it does not repair a weak architecture.

Null safety and the crash class it removes

Kotlin’s type system pushes null handling into the compiler for Kotlin-authored code. It reduces a common class of NullPointerException inside Kotlin modules. It does not remove nulls arriving from Java, reflection or unannotated platform APIs until those boundaries are handled deliberately.

Coroutines against callback nests

Structured concurrency makes asynchronous Android work easier to read and cancel than deep callback chains. It improves maintainability when the team uses it consistently. It is not a performance guarantee on its own.

Java interoperability

This is what most commercial engagements need: call Java from Kotlin and Kotlin from Java in one Gradle project. Teams keep legacy modules while new work ships in Kotlin.

Gradle and the Kotlin DSL

Build scripts can use the Kotlin DSL. That is a tooling choice for the repository, not a product feature for end users. Version alignment between the Kotlin compiler and libraries remains a maintenance concern on every upgrade.

Jetpack Compose, briefly

Compose is Google’s modern UI toolkit for Android. This page does not claim Compose as a delivered product line in apps.csv. Deep Compose versus XML guidance belongs on Android app development.

Where Kotlin does not help

Kotlin is not a cross-platform product on its own. Kotlin Multiplatform, Ktor and server-side Kotlin are not evidenced as delivered lines in apps.csv. Bad module boundaries stay bad after a language change.

Existing Android codebases

Working with an Android app that already ships

Discovery starts with the repository you have: module map, test coverage, Gradle versions and which packages still change every release. Free functional and technical discovery calls come first. Mutual NDA before detailed discussion.

We write new work in Kotlin where it is safe, leave stable Java alone when conversion buys nothing, and only convert hot paths when tests and active feature work justify it. If you need two store-native codebases, Swift plus Kotlin, that decision lives on native mobile app development.

Source code and IP transfer to the client on delivery. Four months free post-launch support is standard in every contract.

Kotlin projects

Kotlin App Development Projects

Five Android products where apps.csv records Kotlin. The first three list Kotlin first in the stack. UDEL is included because it is the Kotlin row not already used on rebuilt Flutter, React Native, cross-platform, native or Android portfolios. No install counts or store ratings are attached here. More shipped work is in our development portfolio and app and software development case studies.

Kotlin first Android

Taxeasy

Client: Taxeasy Solutions Pvt Ltd · Finance · Android

Digital billing and filings on Android: customisable bills and tax invoices, multiple businesses, estimations, quotations, debit and credit notes, delivery challans, low-stock alerts, debtors and creditors, and tax filing surfaces. Stack in apps.csv: Kotlin, React Js, Node JS.

Google Play ↗
Kotlin first Android

Syrocare

Client: Syrotech · Technical Support Platform · Android

Support app for Syrotech OLT and ONT users: register a device by QR or by entering MAC, model and serial, then reach real-time technical support and guided troubleshooting. Framed here as a Kotlin-first Android client for device support, not as an IoT lab story. Stack: Kotlin, Swift, Node Js, React JS, MongoDB.

App Store ↗ Google Play ↗
Kotlin first Android + Web

easy Health

Client: Easy Health Solutions · Healthcare · Android, Web

Healthcare access in India on a Kotlin-led Android client with a web layer: doctor appointments, health records, home healthcare and hospital management. Described here as Kotlin Android delivery for clinical workflows, not as a wearable companion. Stack: Kotlin, Swift, PHP, React JS.

App Store ↗ Google Play ↗
Kotlin in stack Android + Web

UDEL

Client: University of Delaware · Education · Android, Web

University of Delaware Connect: academic and research hub, campus life, athletics, study abroad, multi-campus navigation and admissions resources. Kotlin appears in a multi-surface stack with React JS, Node.js, HTML5 and Swift. Included because this Kotlin row is not already claimed on the rebuilt Flutter, React Native, cross-platform, native or Android portfolios.

App Store ↗ Google Play ↗
Kotlin in stack Android + Web

Homies4U

Client: Homies4U · Real Estate · India · Android, Web

Student accommodation across India: search and filter hostels and PGs, verified listings, landlord portal, booking and availability, community resources and safety features. Kotlin sits mid-stack with React JS, Node.js, HTML5 and Swift. Framed here as the Android Kotlin client inside that product, not as a native dual-codebase case study.

App Store ↗ Google Play ↗
Services

Kotlin app development services

These are language-scoped Android services. They sit beside our mobile app development services when you need the wider mobile programme, not only Kotlin.

Custom Kotlin Android development

New Android applications and modules written in Kotlin against agreed scope.

Java to Kotlin migration support

Incremental conversion plans driven by tests and active feature files, not a forced rewrite.

Mixed Java/Kotlin codebase maintenance

Ongoing delivery on repositories that will remain mixed while product work continues.

Kotlin Android consulting

Architecture and migration advice for teams deciding how much Java to leave alone.

Play Store release support

Store submission support for Android builds after QA on the devices your users run.

Post-launch Kotlin Android support

Four months free post-launch support, standard in every contract, then ongoing maintenance if you choose it.

Process

How a Kotlin engagement runs

No week counts and no published prices on this page. Scope sets both after free discovery.

Stage 1

Free functional and technical discovery calls, mutual NDA first

Functional discovery covers the product and users. Technical discovery covers the repository, Gradle versions, test coverage and release constraints. Mutual NDA before detailed discussion.

Stage 2

Codebase assessment when a Java app already exists

Module map, mixed-language hotspots and conversion candidates are written down before UI promises. Greenfield Kotlin work skips this gate.

Stage 3

Scope document, then proposal and agreement

Discovery becomes a scope document you keep. Proposal and agreement follow that artifact.

Stage 4

Design and build

Kotlin modules, interop with remaining Java, and Android UI work against the agreed backlog.

Stage 5

Testing on the Android versions and devices your users run

QA follows the device and OS matrix written in scope, not a single lab phone.

Stage 6

Play Store submission

Store packaging and submission support after release criteria are met.

Stage 7

Post-launch support, four months free, standard in every contract

Source code and IP transfer on delivery. Four months free post-launch support is standard, then optional ongoing maintenance.

Why Mobulous

Why teams hire us for Kotlin Android work

Evidence before language slogans

Eight apps.csv rows list Kotlin. We describe primary versus mid-stack honestly and do not invent Multiplatform or Ktor delivery.

Migration without theatre

Incremental Kotlin beside Java is the default. Full conversion is recommended only when the codebase and team justify it.

Clear boundary with Android and native pages

This page owns Kotlin-by-name search. Platform Android and dual-codebase native stay on their own URLs.

Verified delivery footprint

700+ apps delivered, 500+ clients, 12+ years since 2013, 30+ countries, 100+ experts.

Reviewed delivery

4.7/5 on Clutch (103 reviews), 4.8/5 on GoodFirms (65+ reviews), 5.0/5 on G2 (5 reviews), 4.3/5 on Google Reviews.

Contract basics that stay the same

ISO 9001:2015, ISO/IEC 27001:2022, CMMI Level 3. Source code and IP transfer on delivery. Four months free post-launch support, standard in every contract.

Client reviews

Verified on Clutch and GoodFirms

"Their friendly nature and open communication set them apart from competitors."

Alexander Bauer
CEO · Kitchen Stories · Berlin, Germany · Verified Clutch review
Verified on Clutch →

"Overall it was a great experience working with Mobulous. They are very professional and stick to their commitments done on the pre-sales stage. The team is well organised and work on the recommendations and feedbacks."

Ankit Ghanghas
E-commerce Development · Verified GoodFirms review
Verified on GoodFirms →

"Mobulous is excellent at interpreting and bringing client ideas to life. The Mobulous team is very responsive and quick to execute client requirements."

Eugene Nyabundi
East African Breweries Ltd · Verified GoodFirms review
Verified on GoodFirms →

Mobulous rates 4.7/5 on Clutch (103 reviews), 4.8/5 on GoodFirms (65+ reviews), 5.0/5 on G2 (5 reviews), and 4.3/5 on Google Reviews. Clutch → · G2 → · GoodFirms →

FAQ

FAQs about Kotlin app development

What is the best Kotlin app development company?

There is no single best vendor for every backlog. Prefer a partner that writes new Android work in Kotlin, leaves stable Java alone when conversion buys nothing, transfers source code and IP on delivery, and states post-launch support in the contract. Ratings such as 4.7/5 on Clutch (103 reviews) are context, not a substitute for those terms.

Which company provides Kotlin app development services?

Mobulous provides Kotlin Android development, Java-to-Kotlin migration support and mixed-codebase maintenance. Apps.csv lists eight projects with Kotlin in the stack. Platform Android depth is on our Android page; dual Swift and Kotlin product builds are on our native page.

Who are the best Kotlin app developers?

Look for engineers who treat interop as the default, can explain what null safety does and does not remove at Java boundaries, and will not sell a full rewrite when incremental conversion is enough. Ask what their last mixed Java/Kotlin repository still looks like in production.

How much does Kotlin app development cost?

Scope determines cost. Free discovery produces a scope document before any proposal. This page does not publish price bands or hourly rates.

Does Google use Kotlin?

Yes. Google made Kotlin a first-class language for Android and recommends it for new Android development. That is why new Mobulous Android modules default to Kotlin. It does not mean every legacy Java line must be rewritten.

Is Kotlin used outside of Android?

Kotlin can target more than Android, including multiplatform and server options in the wider ecosystem. This page does not claim Kotlin Multiplatform, Ktor or server-side Kotlin as delivered Mobulous product lines, because apps.csv does not record them.

How do you develop an Android app using Kotlin?

Agree scope, assess any existing Java repository, build in Kotlin with Java interop where needed, test on the Android versions your users run, then submit to Play Store. Mutual NDA and free discovery come first.

From the blog

Read before you fund a Kotlin migration

Next step

Start with a free discovery call

Bring the Android repository you have, or the product you want to start in Kotlin. 700+ apps delivered, 500+ clients, 12+ years, 4.7/5 on Clutch (103 reviews). Mutual NDA before detailed discussion. Source code and IP transfer on delivery. Four months free post-launch support, standard in every contract.

Related: Android app development · our development portfolio · app and software development case studies · estimate your project.

  • Discovery calls are free
  • Source code and IP transfer on delivery
  • ISO 9001:2015 · ISO/IEC 27001:2022 · CMMI Level 3
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Related: Android app development, our development portfolio, app and software development case studies, estimate your project.