Next.js "Type error: ..." from tsc during next build in CI

By Daniel Zoghalchali·Latchkey

next build runs the TypeScript compiler over your project. Any type error becomes a hard build failure with "Failed to compile" plus the offending file, line, and TS diagnostic.

What this error means

next build aborts with "Failed to compile." and "Type error: Property 'x' does not exist on type 'Y'" (or another TS code), pointing at a file and line. It can fail in CI even when the dev server ran fine.

Failed to compile.

./app/page.tsx:14:21
Type error: Property 'title' does not exist on type 'Post'.

  12 |   return (
> 14 |     <h1>{post.title}</h1>
     |                ^

Common causes

A real type error that dev rendering tolerated

The dev server transpiles without full type-checking, so a type mismatch only surfaces when next build runs tsc.

Type definitions differ in CI

A different installed version of a dependency or @types package changes a signature, producing an error CI sees but a stale local install did not.

How to fix it

Reproduce and fix the type error locally

1. Run npx tsc --noEmit to see the same diagnostics CI sees.
2. Fix the type at the file and line reported, not by widening to any.
3. Re-run next build to confirm it compiles.

npx tsc --noEmit
npm run build

Pin type-providing dependencies

Lock the versions of the package and its @types so CI and local see identical signatures.

npm ci   # install exactly from package-lock.json

How to prevent it

• Run tsc --noEmit in CI before or alongside next build.
• Commit a lockfile so type definitions are identical everywhere.
• Avoid typescript.ignoreBuildErrors, which only hides the failure.

Frequently asked questions

Related guides

References

• Node.js documentation
• npm CLI documentation
• GitHub Actions documentation