Run nimbus dev and Nimbus opens a test dashboard in the browser: test explorer, live results, coverage, watch mode, a schema browser and an Apex REPL. It needs no editor plugin, so it works without VS Code or IntelliJ.
Run nimbus dev and Nimbus starts a local web server (default port 8080) and opens your browser. The dashboard stays connected over WebSocket, so results update as tests run, without a page refresh. If you know the Quarkus Dev UI, this is the same idea for Apex.
It is useful on a machine without a Salesforce IDE, in a browser-only environment, when pairing with someone who does not have the plugin, or when you prefer a dashboard to terminal output.
The Dev UI runs alongside the editor integration. Both share the same daemon, so tests run from VS Code update the Dev UI too.
# Start the Dev UI
nimbus dev
# → Opens http://localhost:8080 in your browser
# → Stays connected via WebSocket
# → Results update live as tests run
# Custom port
nimbus dev --port 3000
# Don't open browser automatically
nimbus dev --no-browser
# Or configure in nimbus.properties
# nimbus.devui.port=8080
# nimbus.devui.open-browser=trueA resizable sidebar holds the test explorer: every class and method in the project, grouped by class. Click to expand a class, click a method to select it. Each entry shows its live status: pending, running, passed, or failed. Run buttons on hover run a single class or method.
Live test results as they complete. Pass/fail per method, duration, failure messages inline. Click any test to see its full output and error trace.
Line coverage percentages per class, updated after every run. It shows which lines are covered and which are not, in the browser.
An Apex REPL. Write and run anonymous Apex in the browser: query data, test expressions, prototype logic.
Every SObject in the project schema, with fields, types and required flags. Useful when writing SOQL and a field name escapes you.
The raw test output log: System.debug() calls, governor limit warnings, trace entries. Scrollable and searchable.
The effective nimbus.properties configuration with the active profile highlighted. It shows what is set, what is overridden, and which file each value came from.
The Execute tab is an Apex REPL against the local database. Write an Apex expression or block and run it immediately, with no test class, no deploy and no org.
It behaves like nimbus exec in the browser, with structured output: results for SObjects and collections, inline System.debug() output, error messages with line numbers.
Useful for prototyping SOQL against seeded data, checking an expression before writing a test, seeing how the runtime handles an edge case, or verifying DML behavior without a full test method.
// In the Execute tab - runs immediately
// Query your seeded data
List<Account> accounts = [
SELECT Id, Name, Industry
FROM Account
WHERE Industry = 'Technology'
LIMIT 5
];
System.debug('Found: ' + accounts.size());
// Test an expression
Decimal result = Math.round(3.7);
System.debug(result); // → 4
// Insert a record and query it back
Account acc = new Account(Name = 'Test');
insert acc;
Account fetched = [SELECT Name FROM Account WHERE Id = :acc.Id];
System.debug(fetched.Name); // → TestClick the Watch button in the toolbar and Nimbus monitors your Apex source files for changes. Save a file and the relevant tests rerun; results update in the browser as they complete.
For multi-package projects, use the Watch scope dropdown to restrict watching to a specific package directory. Only tests related to that package rerun on save, which keeps reruns short in large projects.
The parallel workers panel appears during runs and shows how many test workers are active and which test each is running. Watch mode respects your nimbus.test.parallel setting, so more cores mean faster reruns.
# Start Dev UI with watch mode pre-enabled
nimbus dev --watch
# Or click Watch in the toolbar after the UI opens
# → Monitors force-app/**/*.cls and **/*.trigger
# → Reruns affected tests on every save
# → Results update live in the browser
# Scope watch to a specific package
# Use the Watch ▾ dropdown in the toolbar
# → "All packages" or select a specific pathnimbus dev opens a test dashboard with a test explorer, live results, coverage, a schema browser and an Apex REPL. It needs no editor plugin.