Launch, attach, restart, stop, or detach Java applications. For Maven/Gradle, use project_path plus main_class without IDEA, or select an IDEA launch. Use java_fast_test to run tests without launching an application. Launch and restart wait up to timeout (at most 30 seconds), returning the result if finished or the original background task if still running. After editing a managed Maven/Gradle project, use restart: it detects changed sources, incrementally compiles them, and prefers HotSwap (hotswap=true by default). Incompatible changes use the same compiled outputs to restart the JVM. Set hotswap=false for a real process restart and application reinitialization. apply_method reports hotswap or restart; HotSwap does not refresh framework state or count as a JVM startup. previous_startup_ms reports the prior successful startup duration saved locally for this launch, or null if unavailable. It survives MCP restarts and excludes compilation. A pending restart returns reload_id; observe active_operation and last_reload using java_status. Direct JAR/classpath launches restart their existing artifact without source compilation.

Run selected Java tests in Maven or Gradle projects, incrementally compiling changed sources. Supports JUnit 4/5 and TestNG. No application launch is required, and an existing application is left running. Provide project_path and tests (Class or Class#method); action defaults to run. First-time preparation and compilation can take minutes; subsequent calls reuse unchanged results. Waits up to timeout (maximum 30 seconds); unfinished work returns its test_run_id and continues in the background. Observe it with java_status or cancel it here using action='cancel' and the same test_run_id. If compilation fails before run returns, it includes compiler diagnostics directly. java_status stays compact; use action='result' with test_run_id for background error diagnostics and failed-test details without rerunning tests. This is not the complete Maven/Gradle verification or packaging lifecycle.

Discover local Java processes, inspect a compact application/build overview with status, or request current launch/restart details with status and details=true. Use logs with source=application (default) or source=build for log text. status omits build-log text and detailed launch/restart results. It includes only a Fast Test summary; read test details with java_fast_test(action='result', test_run_id=...).

Observe executed paths and runtime state with breakpoints, exception events, stacks, and variables. Always resume or clean up every suspension.