
Measure and fix the bottlenecks users feel.
Root-cause profiling
We measure startup, TTI, thread load, and memory across JS and native to find what actually slows your app down.
Fixes users feel
Smoother scrolling, faster screens, fewer dropped frames. We tune render paths instead of rewriting features.
Smaller bundles
Tree-shaking and code splitting cut parse and load time. We took Dream11 from 50MB to 11MB, a 78% drop.
Fewer re-renders
We kill wasteful renders and unbatched state updates. Questrade saw 33% fewer re-renders after our pass.
Regression guardrails
Reassure and Rozenite benchmark performance in your CI, so a future commit can't quietly undo the gains.
Low-end device wins
We optimize for the phones most teams ignore, where slow code hurts retention the most.
Scope → Build → Scale
Turn technical limits into shipped fixes.
Scope
We map your problem, align on deliverables, and define success metrics. No surprises once work starts.
Build
Engineers ship with AI-native workflows from sprint one. Code, decisions, and ownership, not discovery decks.
Scale
Expand scope, add platforms, or hand off to your team. The stack, tooling, and raised bar stay with you.
Why teams bet on Callstack
From billion-user apps to React Native core, this is why teams choose Callstack when they need to move fast and get it right.

10 years in React Native. Now shaping agentic engineering.
For a decade, we have helped define how teams ship with React Native. Now we are helping shape how they work with agents.
Founded in 2016 ·Backed by Viking Global Investors
React Foundation members. Core Contributors.
We are founding members of React Foundation and Core Contributors to React Native. You get direct access to people close to the decisions shaping the frameworks you use.
Open source since 2016. Our code runs in your app.
We contribute to React Native and maintain libraries across its ecosystem. Our code runs in apps used by millions of people every day.
39M+
Downloads / month67K+
GitHub stars300+
React Native commits100+ Enterprise clients with 7B+ users.
We work with teams shipping at real scale. You get a partner used to high-stakes products, not learning on your roadmap.


































Agent Conf. The conference for the Agentic era.
The conference we built for the shift from writing code to orchestrating agents.


We are Codex Ambassadors.
We run meetups, workshops, and hands-on sessions that help teams learn Codex and apply it in real work.

10 years in React Native. Now shaping agentic engineering.
For a decade, we have helped define how teams ship with React Native. Now we are helping shape how they work with agents.
Founded in 2016 ·Backed by Viking Global Investors
React Foundation members. Core Contributors.
We are founding members of React Foundation and Core Contributors to React Native. You get direct access to people close to the decisions shaping the frameworks you use.
Open source since 2016. Our code runs in your app.
We contribute to React Native and maintain libraries across its ecosystem. Our code runs in apps used by millions of people every day.
39M+
Downloads / month67K+
GitHub stars300+
React Native commits100+ Enterprise clients with 7B+ users.
We work with teams shipping at real scale. You get a partner used to high-stakes products, not learning on your roadmap.


































Agent Conf. The conference for the Agentic era.
The conference we built for the shift from writing code to orchestrating agents.


We are Codex Ambassadors.
We run meetups, workshops, and hands-on sessions that help teams learn Codex and apply it in real work.
Let’s find the right path for your product.
Whether you’re planning new work or unblocking an existing product, we’ll help you choose the right path forward.
How do I know if my React Native app has performance issues?
Performance problems aren't always obvious in development. If you see slow startup, janky animations, dropped frames, high memory use, or poor retention metrics, it's likely your app needs optimization. We use profiling tools to identify and validate these issues with real data.
Do I need to rewrite parts of the app to improve performance?
Not necessarily. Most improvements come from optimizing rendering patterns, bundling, and resource handling, without rewriting core features. In brownfield or legacy apps, we focus on targeted improvements that deliver results without disrupting existing workflows.
What’s included in a performance audit?
We assess startup time, UI responsiveness, memory usage, JS thread pressure, and bundle size. The audit includes a detailed report with key findings, prioritized recommendations, and potential impact estimates.
Can you help us implement the fixes too?
Yes. We offer hands-on implementation, advisory support, or can work embedded with your team. Our engineers apply fixes directly or help your team ship them safely.
Will this affect our release cycle or CI/CD pipeline?
No. We work alongside your existing release process and can integrate performance monitoring directly into CI to help you catch regressions without slowing down delivery.
What kind of results should we expect?
While results vary, teams typically see faster startup, smoother UI, reduced crash rates, and better retention, especially on low-end devices. All improvements are measurable, and we help you track them before and after implementation.
Can you reduce our bundle size?
Yes. We use tree-shaking and code splitting to cut parse and load time. We took Dream11 from 50MB to 11MB, a 78% drop.
Can you optimize for low-end devices?
Yes. We optimize for the phones most teams ignore, where slow code hurts retention the most. Those users often feel the gains first.
Fast apps keep users
Send us the slow flows. We'll find the root causes and tell you what's worth fixing, with numbers, not guesses.
We had been struggling with React Native application performance until we met Callstack.
Open Source
Want to build it on your own?
We open-source the tools behind our delivery model.
Use them, fork them, or let us run them for you.
Insights



















































































































