How do const widgets help reduce the cost of a rebuild?

Short answer

const creates a configuration that can be shared at compile time, which lets Flutter skip static parts and do less checking during an update.

Explanation

Use const when all inputs are compile-time constants, but do not make it a cosmetic goal. First understand which subtree is being rebuilt, then reduce the work inside build and measure performance when needed.

Common mistakes

• Believing const prevents the parent from rebuilding altogether.
• Adding complexity just to reach const on a changing value.

Follow-up questions

• What are the basic stages of producing a frame in Flutter?

Sources

• Flutter docs — Performance best practices