Reactive State Management with Signals in Vaadin 25

Use the Vaadin MCP tools (search_vaadin_docs) to look up the latest documentation whenever uncertain about a specific API detail. Always set vaadin_version to "25.1" and ui_language to "java".

For an exact Java API signature or to read source, use the javadoc MCP (mcp__javadoc__* — find via ToolSearch javadoc if not loaded) to read Javadoc and sources from Maven Central instead of unpacking jars from ~/.m2.

What Signals Are

Signals are a reactive state management system for Vaadin Flow. A signal holds a value, and when that value changes, all dependent parts of the UI automatically update without manually adding and removing change listeners.

Key properties:

• Reactive -- changes propagate automatically to dependent UI
• Automatic dependency tracking -- effects detect which signals they depend on
• Immutable values -- signals work best with immutable types (String, Integer, Java records)
• Thread-safe -- signals can be updated from any thread without ui.access()
• Two categories -- local signals for single-session UI state, shared signals for multi-user/transactional state

Local vs Shared: Which to Use