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React Compiler automatically memoizes eligible React components and hooks during the build, helping avoid repeated rendering work when relevant inputs have not changed. To use it, install and configure it in your build pipeline, then verify its behavior with linting, tests, and profiling. It can reduce unnecessary work, but it does not guarantee that every app will become faster.
What React Compiler automatic memoization does
React Compiler analyzes components and hooks at build time and adds memoization based on that analysis. This can let React reuse a component’s output or a calculation when its inputs have not meaningfully changed, so unrelated updates elsewhere in a parent do not necessarily make every child do the same work again. The compiler is a build-time optimization, not a runtime performance switch. React’s compiler documentation describes its purpose and behavior.
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Memoization is an optimization, not a promise that React will never render a component. Nor does the compiler memoize every JavaScript function: a standalone helper outside a component or hook is not automatically memoized, and a cached calculation is not shared among different components or hooks. If an expensive helper is called by several components, each may still perform its own work; profile the actual workload before adding a separate caching layer. The compiler directive documentation covers these boundaries.
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The exact integration depends on your build tool and project versions, so use the current React Compiler installation guide for the matching setup. The guide recommends installing babel-plugin-react-compiler as a development dependency. In a Babel configuration, place the compiler plugin first in the plugin array so it can analyze the original source before other transformations.
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The official guide also documents Vite integration and directs React Native/Metro and other environments to their respective setup instructions. Do not assume a Babel configuration applies unchanged to another build system.
React version compatibility
The compiler is designed to work best with React 19, and most React 19 apps can use the default configuration. React 17 and 18 are also supported, but their setup requires the react-compiler-runtime package and a target set to the project’s React version. Confirm the exact package and build-tool requirements in the live installation and configuration references before changing a project; these implementation details can evolve.
Add lint diagnostics
React recommends eslint-plugin-react-hooks for compiler diagnostics. Its compiler rules can flag violations of React’s rules and code that cannot be optimized. An affected component or hook is skipped; that does not prevent the compiler from optimizing other eligible code. Review the installation guide for the current lint setup.
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A new or well-understood React 19 app can begin with the standard integration and lint feedback. For a large or higher-risk codebase, adopt the compiler incrementally: enable a limited area, check correctness and performance, and expand only when results support it. React documents compilation modes and opt-in controls in its compilation mode and directive references.
| Approach | How it works | When it fits |
|---|---|---|
infer mode |
The compiler infers which eligible components and hooks to optimize. | A project ready for broader, default compiler adoption. |
annotation mode |
Only functions opted in with "use memo" are compiled. |
A gradual rollout where teams want explicit control over scope. |
all mode |
Compiles all functions in scope. | Use only when its broader behavior is appropriate for the project. |
For annotation mode, put "use memo" at the beginning of a function to opt it in. A module-level directive can affect functions in that file. Use "use no memo" to exclude a function, including when a module-level directive would otherwise apply. Keep a clear reason for each opt-out so the exception remains understandable. See the directive reference for exact rules.
Verify operation and measure results
React DevTools can show a “Memo ✨” badge on optimized components, and build output can contain compiler-generated memoization logic. These checks show that compilation is occurring; they do not prove that a user-visible interaction got faster. Measure the relevant interaction in your own app and compare before and after under representative conditions. The installation guide explains the verification signals.
- Use lint output to find code the compiler skips or cannot optimize.
- Run unit and end-to-end tests to catch behavioral changes.
- Profile the interaction or render work you want to improve, rather than assuming every component needs optimization.
Keep or remove useMemo, useCallback, and memo?
For new code, React generally recommends relying on compiler memoization rather than routinely adding useMemo, useCallback, or React.memo. Those APIs remain available when you need more precise control, such as stabilizing a value that is an effect dependency. The compiler applies the equivalent of component memoization automatically in eligible cases, but manual memoization is still a valid tool. See React’s memo reference and compiler documentation.
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Account for correctness and library distribution
React announced React Compiler 1.0 as its first stable release on October 7, 2025, describing it as production-ready and noting use on major apps at Meta. That is the React team’s characterization, not independent comparative benchmark evidence. The announcement also warns that some violations of the Rules of React cannot always be detected statically. A changed memoization pattern can affect identity-sensitive code, including effects that depend on a value whose identity changes differently. Follow the Rules of React, maintain continuous end-to-end tests, and, where coverage is weak, pin the compiler to an exact version and upgrade deliberately. Read the React Compiler 1.0 announcement.
If you publish a library that supports React versions below 19, the library guidance recommends making react-compiler-runtime a direct dependency and configuring the minimum supported React target. Test the library both with and without compilation so consumers’ build choices do not leave behavior unverified. See Compiling Libraries.
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