# Callstack > Callstack builds and scales React and React Native products, and helps teams deliver with AI agents, custom workflows, and testing they control. React Native experts and React Foundation member helping enterprise teams ship faster with AI-native engineering, agentic infrastructure, and 10+ years of cross-platform expertise. Every page of https://www.callstack.com is also available as Markdown: request it with `Accept: text/markdown` or append `.md` to the path (`/index.md` for the home page). ## When to use Callstack - You need senior React or React Native engineers to build, extend or rescue a cross-platform product (iOS, Android, web, desktop, TV, VR) from one codebase. - You are moving a codebase to AI-native delivery: agentic workflows, custom coding agents, AI-driven QA and testing, self-hosted CI/CD for agents, or AI SDLC advisory. - You face a hard React Native problem: performance, the New Architecture migration, upgrades, brownfield integration into existing native apps, native modules or C++/Rust shared cores. - You need AI features in a product (generative AI, on-device models, custom or private models) shipped to production quality. - You want training for an engineering team on React Native, React or AI-assisted development. - You depend on Callstack open source (React Native Paper, Re.Pack, Rock, Reassure, React Native Testing Library, Agent Device, …) and need maintainers’ help or a feature. Callstack is probably not the right fit for: - Native-only (Swift/Kotlin without React Native), game-engine or backend-only projects with no React or React Native front end. - Off-the-shelf SaaS or app templates: Callstack is an engineering services company, not a product vendor. Contact: hello@callstack.com · https://www.callstack.com/contact ## Services - [Services](https://www.callstack.com/services): All engineering and agentic-delivery services. - [Agentic Delivery](https://www.callstack.com/agentic-delivery): AI-native delivery: agents, infrastructure, adoption and governance. - [AI-Native Engineering](https://www.callstack.com/ai-native-engineering): Expert React and React Native engineering. - [Technology](https://www.callstack.com/technology): How Callstack builds with agents. - [Brownfield](https://www.callstack.com/brownfield): Migrating existing native apps to React Native with AI. - [Case studies](https://www.callstack.com/case-studies): Client work and results. - [Contact](https://www.callstack.com/contact): Start a project or ask a question. ## Learn - [Blog](https://www.callstack.com/blog): Articles on React, React Native and AI engineering. - [Tutorials](https://www.callstack.com/tutorials): Video tutorials. - [Podcast](https://www.callstack.com/podcast): React Universe On Air episodes. - [Events](https://www.callstack.com/events): Conferences, talks and meetups. - [Webinars](https://www.callstack.com/webinars): Webinars and live streams. - [Ebooks](https://www.callstack.com/ebooks): Free guides, including The Ultimate Guide to React Native Optimization. - [Insights](https://www.callstack.com/insights): Topic hubs grouping articles, talks and guides. - [Newsletter](https://www.callstack.com/newsletter): React and React Native newsletter archive. ## Company - [About us](https://www.callstack.com/about-us): Who Callstack is. - [Team](https://www.callstack.com/team): Engineers and leadership. - [Careers](https://www.callstack.com/careers): Open roles. - [Media kit](https://www.callstack.com/media-kit): Logos, brand assets and press contacts. ## Capabilities - [AI SDLC Advisory](https://www.callstack.com/capabilities/ai-sdlc-advisory): Move from AI-assisted coding to agentic product delivery. - [AI-Driven QA & Testing](https://www.callstack.com/capabilities/ai-driven-qa-testing): Automate app testing with AI agents. - [Architecture & Performance](https://www.callstack.com/capabilities/architecture-performance): Solve your hardest engineering challenges. - [Custom & Private Models](https://www.callstack.com/capabilities/custom-private-models): Use the right AI model, locally or in the cloud. - [Custom Agents](https://www.callstack.com/capabilities/custom-agents): Put agents on recurring engineering work. - [End-to-End Product Development](https://www.callstack.com/capabilities/end-to-end-product-development): Ship every platform from one codebase. - [Enterprise Infrastructure](https://www.callstack.com/capabilities/self-hosted-ci-cd-infrastructure): Build a stronger platform for React Native delivery. - [Feature Development](https://www.callstack.com/capabilities/feature-development): Ship priority features with React and React Native experts. - [Migrations & Upgrades](https://www.callstack.com/capabilities/ai-assisted-migrations): Execute complex migrations fast and with confidence. - [Team Training](https://www.callstack.com/capabilities/team-training): Build stronger engineering teams. ## Service details - [AI Developer Training](https://www.callstack.com/services/ai-developer-training): Hands-on training that moves engineers from ad hoc AI experimentation to deliberate, effective daily use. - [AI Vibe Coding Cleanup](https://www.callstack.com/services/ai-vibe-coding-cleanup): Review, refactor, and harden AI-generated code from Claude Code, Cursor, or any LLM with tests, docs, and human-owned quality. - [AI-Generated Code Validation](https://www.callstack.com/services/ai-generated-code-validation): Validate AI-written UI and logic on real devices before merge, so agent speed never ships regressions or weak implementations. - [AI-Native Test Automation](https://www.callstack.com/services/quality-assurance): Build agentic QA infrastructure on Agent Device so one engineer can run secure, real-device test automation at production scale. - [Accessibility Audits (EEA)](https://www.callstack.com/services/accessibility-audits-eea): Catch accessibility issues during delivery with automated audits mapped to the accessibility requirements that apply across the EEA. - [Build & Test Acceleration](https://www.callstack.com/services/build-test-acceleration): Shorten build and test feedback loops with caching, parallelization, and runners tuned to your workloads. - [C++ Development](https://www.callstack.com/services/c-development): Design and build C++ for graphics, media, and real-time processing that powers demanding apps across iOS, Android, and beyond. - [C++ Library Integration](https://www.callstack.com/services/c-library-integration-for-react-native): Wrap existing C, C++, Go, or Rust libraries as typed React Native modules for fast, cross-platform native performance. - [CI/CD Automation Agents](https://www.callstack.com/services/ci-cd-automation-agents): Agents that fix pipelines, rerun flaky tests, manage release gates, and handle rollout steps across delivery. - [CI/CD Modernization](https://www.callstack.com/services/ci-cd-modernization): Replace brittle pipelines with faster, observable delivery workflows built for agent-speed engineering. - [Code Review Agents](https://www.callstack.com/services/code-review-agents): Deploy agents that check PRs for regressions, missing tests, and weak patterns before human review. - [Cross-Platform Code Verification](https://www.callstack.com/services/cross-platform-code-verification): Validate shared code across iOS, Android, web, and TV in one QA flow, so platform-specific issues cannot hide. - [Custom High-Performance Renderers](https://www.callstack.com/services/custom-high-performance-renderers): Build WebGPU, Skia, or Filament renderers for 60fps, pixel-perfect experiences when standard components cannot meet the bar. - [Delivery Cost Optimization](https://www.callstack.com/services/delivery-cost-optimization): Reduce spend on hosted runners, device clouds, and release tooling by moving the right parts of the stack in-house. - [Desktop App Development](https://www.callstack.com/services/desktop-app-development): Build Windows, macOS, and Linux apps from one codebase, with native performance, AI features, and production-ready delivery. - [Documentation Agents](https://www.callstack.com/services/documentation-agents): Agents that keep technical docs, changelogs, and release notes aligned with code changes automatically. - [Expo Development](https://www.callstack.com/services/expo-development): Design, build, and ship Expo apps from MVP to production scale with Core Contributors, EAS expertise, and AI-native engineering. - [Generative AI Development](https://www.callstack.com/services/generative-ai-app-development): Build AI products with chat, agents, tool use, memory, and cross-platform architecture across mobile, web, desktop, and TV. - [Internal Tool Agents](https://www.callstack.com/services/internal-tool-agents): Connect agents to tickets, repos, CI, Slack, and internal systems with scoped access and clear operating rules. - [LLM Fine-Tuning](https://www.callstack.com/services/llm-fine-tuning): Fine-tune models on your codebase, conventions, and domain, so outputs match how your teams actually build. - [Maintenance Agents](https://www.callstack.com/services/maintenance-agents): Agents that handle cleanup, dependency updates, deprecated APIs, and repo hygiene before they block delivery. - [Migration to Expo](https://www.callstack.com/services/migration-to-expo): Move your React Native app to Expo and EAS for faster builds, simpler releases, and full access to the modern ecosystem. - [Migration to Modular Architecture](https://www.callstack.com/services/migration-to-modular-architecture): Break a monolithic app into independently deployed mini-apps, so teams build and ship in parallel without blocking each other. - [Migration to New Architecture](https://www.callstack.com/services/new-architecture-migration): Move to React Native's New Architecture with Fabric, TurboModules, and JSI while keeping delivery moving and quality under control. - [Migration to Next.js](https://www.callstack.com/services/migration-to-nextjs): Move legacy React and SPA apps onto Next.js for server rendering, streaming, edge delivery, and measurable SEO and performance gains. - [Migration to React Native](https://www.callstack.com/services/migration-to-react-native): Move native apps to React Native faster with custom AI agents doing the repetitive work and expert engineers owning quality. - [Migration to Self-Hosted Infrastructure](https://www.callstack.com/services/migration-to-self-hosted-infrastructure): Move builds, CI/CD, and delivery off hosted platforms onto infrastructure you own, with full control over cost, security, and operations. - [Mobile App Development](https://www.callstack.com/services/mobile-app-development): Build iOS and Android apps from one codebase with native performance, enterprise-grade quality, and AI-native delivery speed. - [Model Evaluation](https://www.callstack.com/services/model-evaluation): Benchmark candidate models against your real engineering tasks to pick the right one and prove it works. - [Module Federation Development](https://www.callstack.com/services/module-federation-development): Build secure federated architecture for mobile, web, and desktop so teams ship independent modules without slowing the core app. - [Next.js Development](https://www.callstack.com/services/next-js-development): Ship fast Next.js apps with server rendering, performance tuning, migrations, and AI-native workflows led by senior React engineers. - [Node.js Development](https://www.callstack.com/services/nodejs-development): Build backends, APIs, and tooling in Node.js that share one language and one skill set with your React and React Native frontends. - [OTA Rollout Management](https://www.callstack.com/services/ota-rollout-management): Ship fixes and changes between store releases with staged OTA rollouts, health checks, and instant rollback. - [On-Device AI](https://www.callstack.com/services/run-ai-directly-on-the-device-for-speed-privacy-and-control): Run AI directly on iOS and Android with private models, offline support, low latency, and data that stays on the device. - [On-Prem & Cloud QA Execution](https://www.callstack.com/services/on-prem-cloud-qa-execution): Run the same QA agent on your own infrastructure or in hosted environments, matched to security policy and scale. - [On-Premise LLM Deployment](https://www.callstack.com/services/on-premise-llm-deployment): Stand up self-hosted LLMs so sensitive code and data never leave your infrastructure. - [React Development](https://www.callstack.com/services/react-development): Build, modernize, and scale React apps with senior engineers and AI-native workflows that keep architecture, quality, and delivery moving. - [React Native Brownfield Integration](https://www.callstack.com/services/react-native-brownfield): Add React Native to existing iOS and Android apps screen by screen, with aligned releases, OTA support, and expert review. - [React Native Development](https://www.callstack.com/services/react-native-development): Work with React Native Core Contributors to ship iOS, Android, and 10+ platforms from one codebase with AI-native engineering. - [React Native Modules Development](https://www.callstack.com/services/react-native-modules-development): Build TurboModules and NitroModules that expose native SDKs through clean, typed JavaScript APIs across iOS and Android. - [React Native Performance Optimization](https://www.callstack.com/services/react-native-performance-optimization): Profile JS and native layers, fix startup, memory, and dropped-frame issues, and prove every performance gain with measurement. - [React Native Trainings](https://www.callstack.com/services/react-native-trainings): Train your team on React Native tooling, architecture, AI-native workflows, and production patterns with Core Contributors. - [React Native Upgrades](https://www.callstack.com/services/react-native-upgrades): Upgrade React Native safely, resolve native module issues, meet store requirements, and stay inside the supported release window. - [Real-Device Testing](https://www.callstack.com/services/real-device-testing): Test on physical iOS and Android hardware with agent-driven runs, where gestures, performance, and native integrations actually behave. - [Release Automation](https://www.callstack.com/services/release-process-optimization): Rebuild React Native release systems, CI/CD, OTA updates, and rollbacks on infrastructure your team owns and controls. - [Release Monitoring & Observability](https://www.callstack.com/services/monitoring-observability): Build end-to-end observability across JavaScript, native, and backend with OpenTelemetry tied directly to your releases. - [Shared Native Core](https://www.callstack.com/services/shared-native-core-for-cross-platform-apps): Build one C++ or Rust core for mobile, web, desktop, and TV so teams avoid per-platform rewrites and logic drift. - [Streaming App Development](https://www.callstack.com/services/streaming-app-development): Build streaming apps for TV, mobile, and web with smooth playback, remote-first UX, CI/CD, and production-grade reliability. - [Super App Development](https://www.callstack.com/services/super-app-development): Build production-ready super apps with mini-app architecture, independent releases, and a Re.Pack foundation proven at scale. - [Tech Debt Reduction](https://www.callstack.com/services/scalability-engineering): Audit architecture, structure, and workflows, then fix the debt that blocks velocity, releases, and team scale first. - [Upgrade Agents](https://www.callstack.com/services/upgrade-agents): Agents that run framework, dependency, and React Native upgrades with repeatable steps and verification built in. - [VR App Development](https://www.callstack.com/services/vr-app-development): Build immersive VR apps with React Native, WebXR, and AI-native workflows that move prototypes from concept to real devices faster. - [Web App Development](https://www.callstack.com/services/web-app-development): Build fast, typed web apps with React and Next.js, ready to extend across mobile, desktop, or TV from one codebase. ## Developer resources (open source) Callstack maintains these libraries and tools; source on GitHub (https://github.com/callstack, https://github.com/callstackincubator). Overview: https://www.callstack.com/open-source - [Rock](https://github.com/callstack/rock): Modular toolkit for teams building React Native apps - [Re.Pack](https://github.com/callstack/repack): A webpack-based toolkit to build your React Native application with full support of webpack ecosystem - [Reassure](https://github.com/callstack/reassure): Performance testing companion for React and React Native - [Apex](https://apex.callstack.com): Agentic coding model for mobile and web - [Voltra](https://github.com/callstackincubator/voltra): Voltra lets React Native developers build native iOS Live Activities, Dynamic Island layouts, and widgets as React components without writing Swift. - [Skill Gym](https://github.com/callstackincubator/skillgym): Prove your agent skills work before you ship them - [Rozenite](https://github.com/callstackincubator/rozenite): Plug-and-play panels for React Native DevTools. Install, enable, and start debugging in minutes. - [React Navigation](https://github.com/react-navigation/react-navigation): Routing and navigation for your React Native apps - [React Native Vision OS](https://github.com/callstack/react-native-visionos): A framework for building native visionOS applications using React Native - [React Native Testing Library](https://github.com/callstack/react-native-testing-library): Simple and complete React Native testing utilities that encourage good testing practices - [React Native Slider](https://github.com/callstack/react-native-slider): React Native component exposing Slider from iOS and SeekBar from Android - [React Native Sandbox](https://github.com/callstackincubator/react-native-sandbox): Run multiple, isolated React Native instances within a single application - [React Native Paper](https://github.com/callstack/react-native-paper): Material Design for React Native (Android & iOS) - [React Native Pager View](https://github.com/callstack/react-native-pager-view): React Native wrapper for the Android ViewPager and iOS UIPageViewController - [React Native Legal](https://github.com/callstackincubator/react-native-legal): Automagically generate license acknowledgements for your React Native app & any JS project - [React Native Harness](https://github.com/callstackincubator/react-native-harness): Harness brings Jest-style tests to real native environments so you can test TurboModules like you would test your React Native app: with JavaScript. - [React Native Evals](https://github.com/callstackincubator/evals): A benchmark suite for evaluating how coding models solve real React Native tasks - [React Native Community CLI](https://github.com/react-native-community/cli): Command line tools to help you build React Native apps - [React Native Builder Bob](https://github.com/callstack/react-native-builder-bob): Simple set of CLIs to scaffold and build React Native libraries for different targets - [React Native Brownfield](https://github.com/callstack/react-native-brownfield): Incrementally move your iOS and Android apps to React Native without breaking - [React Native Bottom Tabs](https://github.com/callstackincubator/react-native-bottom-tabs): Native Bottom Tabs for React Native - [React Native AI](https://github.com/callstackincubator/ai): On-device LLM execution in React Native with Vercel AI SDK compatibility - [Liquid Glass](https://github.com/callstack/liquid-glass): iOS Liquid Glass in React Native - [Linaria](https://github.com/callstack/linaria): Zero-runtime CSS in JS library - [Agent Skills](https://github.com/callstackincubator/agent-skills): Callstack’s best practices on React Native performance optimization, upgrading, CI workflows, and brownfield migrations - [Agent React DevTools](https://github.com/callstackincubator/agent-react-devtools): Gives AI agents access to React DevTools - [Agent Device](https://github.com/callstackincubator/agent-device): CLI to control iOS and Android devices for AI agents ## Optional - [llms-full.txt](https://www.callstack.com/llms-full.txt): Every published article, episode, event and case study with summaries, plus full article text. - [Sitemap](https://www.callstack.com/sitemap-index.xml): Every indexable URL.