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Nightwatch DevTools

Nightwatch adapter for WebdriverIO DevTools - brings the same visual debugging UI to your Nightwatch test suite with zero test code changes.

Installation​

npm install @wdio/nightwatch-devtools

Setup​

Standard Nightwatch (mocha-style)​

// nightwatch.conf.cjs
const nightwatchDevtools = require('@wdio/nightwatch-devtools').default

module.exports = {
  src_folders: ['tests'],

  test_settings: {
    default: {
      desiredCapabilities: {
        browserName: 'chrome',
        // Required for network request capture
        'goog:loggingPrefs': { performance: 'ALL' }
      },
      globals: nightwatchDevtools({ port: 3000 })
    }
  }
}

Run your tests as normal - the DevTools UI opens automatically in a new browser window:

nightwatch

No changes to your test files are needed.

Cucumber / BDD​

Import cucumberHooksPath alongside the main export and pass it to the Cucumber require option. This registers Before / After scenario hooks that mirror the WebdriverIO service's beforeScenario / afterScenario behaviour.

// nightwatch.conf.cjs
const nightwatchDevtools = require('@wdio/nightwatch-devtools').default
const { cucumberHooksPath } = require('@wdio/nightwatch-devtools')

module.exports = {
  src_folders: ['features/step_definitions'],

  test_runner: {
    type: 'cucumber',
    options: {
      feature_path: 'features',
      require: [cucumberHooksPath] // <-- register DevTools Cucumber hooks
    }
  },

  test_settings: {
    default: {
      desiredCapabilities: {
        browserName: 'chrome',
        'goog:loggingPrefs': { performance: 'ALL' }
      },
      globals: nightwatchDevtools({ port: 3000 })
    }
  }
}

Configuration Options​

OptionTypeDefaultDescription
portnumber3000Port for the DevTools backend server. Auto-incremented if already in use.
hostnamestring'localhost'Hostname the backend server binds to.
screencastScreencastOptions{ enabled: false }Per-session .webm video recording. See Screencast below.
bidibooleanfalseOpt into WebDriver BiDi capture for browser console + JS exceptions + network. Requires webSocketUrl: true in your capabilities and a BiDi-capable chromedriver. When attached, the per-command Chrome perf-log network path is gated off so requests don't duplicate.
mode'live' | 'trace''live'live opens the DevTools UI; trace skips it and writes a portable artifact instead. See Trace Mode.
traceFormat'zip' | 'ndjson-directory''zip'Trace artifact layout. Only applies when mode: 'trace'.
traceGranularity'session' | 'spec' | 'test''session'One trace per session / spec file / test. 'test' writes each to test-results/<spec>-<title>-<browser>[-retryN]/trace.zip. Only applies when mode: 'trace'. See Trace Mode. Caveat: the BDD describe/it interface collapses to a single session-scoped slice (see Per-test slicing).
tracePolicy'on' | 'retain-on-failure' | 'retain-on-first-failure' | 'on-first-retry' | 'on-all-retries' | 'retain-on-failure-and-retries''on'Which traces to keep. Pairs with traceGranularity: 'test'. Only applies when mode: 'trace'.
filmstripbooleantrueRecord a dense, continuous screencast filmstrip into the trace for scrubbable playback in the trace player — not just one frame per action. Runs the screencast recorder (polling mode on Nightwatch) for the session. Only applies when mode: 'trace'.
screenshot'off' | 'on' | 'only-on-failure''off'Per-test screenshot. Trace mode + traceGranularity: 'test' only. Produce-only — the PNG is written to the trace output dir (and the manifest when emitArtifactsManifest: true); not attached inline to Allure (see note below).
video'off' | TraceRetentionPolicy'off'Per-test video slice, retained per the given policy (e.g. 'retain-on-failure'). Trace mode + traceGranularity: 'test' only. A non-off value starts the screencast recorder itself — you do not also need filmstrip or screencast.enabled. Produce-only — the .webm is written to the trace output dir (and the manifest when emitArtifactsManifest: true); not attached inline to Allure.
emitArtifactsManifestbooleanfalseWrite the devtools-artifacts-<sessionId>.json manifest (the generic index reporters/CI consume to discover produced artifacts) next to the trace. Opt-in for Nightwatch — it has no live Allure signal to auto-detect against, so unlike WDIO/Selenium it never auto-enables. Only applies when mode: 'trace'.
captureAssertionsbooleantrueCapture assertions as trace action rows — node:assert plus native browser.assert/browser.verify, including negated .not.* matchers. Set false to opt out.

Inline Allure attachment is not supported for Nightwatch. Its official nightwatch-allure reporter is post-hoc (no live attach API), and allure-js-commons' attachment() no-ops in a Nightwatch run. So screenshot / video artifacts are produced (files, plus the artifacts manifest when emitArtifactsManifest: true) in the trace output dir but not attached to an Allure test. Per-test slicing — and therefore these artifacts — is meaningful for the Cucumber and exports-object interfaces; the BDD describe/it interface collapses to session granularity, so the per-test gate no-ops there.

globals: nightwatchDevtools({
  port: 3000,
  hostname: 'localhost',
  screencast: { enabled: true },
  bidi: true
})

Screencast​

Record a continuous .webm video of the browser session. The recording starts on the first session the plugin sees and is finalized in Nightwatch's after() hook.

Polling mode only. Nightwatch doesn't expose a stable CDP escape hatch the way WebdriverIO (browser.getPuppeteer()) and Selenium (driver.createCDPConnection) do, so the screencast captures frames by calling browser.takeScreenshot() at a fixed interval. Works on every browser Nightwatch supports.

globals: nightwatchDevtools({
  port: 3000,
  screencast: { enabled: true, pollIntervalMs: 200 }
})
OptionTypeDefaultNotes
enabledbooleanfalseMaster switch.
pollIntervalMsnumber200Screenshot interval (ms). Lower = smoother video, more WebDriver round-trips. 200 ms ≈ 5 fps.
captureFormat'jpeg' | 'png''jpeg'Per-frame pixel format handed to the ffmpeg encoder before the final .webm mux. In polling mode the source screenshots are always captured as PNG, so this does not change the capture - only the format the encoder receives per frame.
maxWidth / maxHeight / quality--CDP-only options, ignored in polling mode. Listed for shape compatibility with the WDIO/Selenium adapters.

Prerequisites: fluent-ffmpeg (already a runtime dep of the package) plus the ffmpeg binary on PATH. macOS: brew install ffmpeg. Linux: apt install ffmpeg. Without ffmpeg the recorder still runs but the encode step logs a warning and skips writing the file.

Output: the video file is written next to the test file that just ran (with nightwatch.conf.* directory as a fallback, then process.cwd() as a last resort). The full path appears in the Nightwatch log line 📹 Screencast video: <path> and the video is also streamed to the dashboard's Screencast tab.

For the full screencast feature reference (browser support, output paths across all three adapters), see the Screencast page.

BiDi capture (opt-in)​

Enable WebDriver BiDi capture for browser console messages, JS exceptions, and network requests. Equivalent to the path selenium-devtools uses - both adapters share the same attach logic in @wdio/devtools-core.

globals: nightwatchDevtools({
  port: 3000,
  bidi: true
})

You also need webSocketUrl: true in your capabilities so chromedriver actually exposes the BiDi channel:

desiredCapabilities: {
  browserName: 'chrome',
  webSocketUrl: true,                           // ← enables BiDi
  'goog:chromeOptions': { /* ... */ }
}

When BiDi is attached, the per-command Chrome performance-log network capture path is gated off so requests don't appear twice in the dashboard. If webSocketUrl is missing or the chromedriver version doesn't expose BiDi, the attach silently fails and the perf-log fallback continues to work.

Trace mode​

Headless capture path — no DevTools UI window opens. At session end the adapter writes a portable trace-<sessionId>.zip (or directory) into a test-results/ folder (next to the resolved test / config directory), with the same shape as the WebdriverIO trace artifact.

globals: nightwatchDevtools({
  mode: 'trace',
  traceFormat: 'ndjson-directory'  // optional; default 'zip'
})

The backend port-bind, UI window, and screencast option are all skipped in trace mode. For the full feature reference (artifact contents, viewer, mobile testing, when to pick zip vs ndjson-directory), see the Trace Mode page.

Nightwatch shares the same trace pipeline as the WebdriverIO and Selenium adapters, so the artifact shape is identical no matter which adapter produced it. A Nightwatch trace carries the full per-action capture — a screenshot, the depth-indented accessibility-tree snapshot, the interactable-element list, and the Markdown transcript — so it opens in the show-trace player with DOM/snapshot time-travel, the A11y and Transcript tabs, the pick-locator element overlay, and (for Cucumber) Feature → Scenario → Step nesting.

Open a trace with the show-trace bin, shipped with @wdio/nightwatch-devtools (no extra dependency):

npx show-trace test-results/trace-<sessionId>.zip   # in a project that installs the adapter
pnpm show-trace test-results/trace-<sessionId>.zip  # from the devtools monorepo

See the Trace Player page for the full walkthrough and keyboard shortcuts.

Per-test slicing & the BDD describe/it caveat​

The per-test options — traceGranularity: 'test', and the tracePolicy, screenshot, and video options that pair with it — need a per-test hook to cut each test's slice. The exports-object (mocha-style) interface and Cucumber (per-scenario hooks) expose one, so they get real per-test slicing. The BDD describe/it interface is the exception: Nightwatch runs each it() internally and fires the plugin's per-test hook only once per module, so traceGranularity: 'test' collapses to a single session-scoped slice keyed to the first test. The artifacts manifest still lists every testcase with its correct state; only the per-test slice/artifact keying collapses. Session- and spec-granularity traces are unaffected.

Examples​

Working examples live in the repo's top-level examples/ directory. Build the workspace once (pnpm install && pnpm build), then run from the repo root:

DirectoryRunnerCommand
examples/nightwatch/Nightwatch mocha-stylepnpm demo:nightwatch

Features​

The Nightwatch adapter provides the same DevTools UI experience as WebdriverIO. Every feature below is captured automatically with the base globals: nightwatchDevtools({ port: 3000 }) setup — no per-feature config (network logs additionally need 'goog:loggingPrefs': { performance: 'ALL' }, shown in Setup). Links go to each feature's full reference.

Screencast is the one feature with its own options (full list under Screencast):

globals: nightwatchDevtools({ port: 3000, screencast: { enabled: true, pollIntervalMs: 200 } })

Limitations​

Nightwatch does not provide the same depth of framework hooks as WebdriverIO, so there are a few differences from the WDIO DevTools service:

LimitationDetail
No native command hooksNightwatch has no beforeCommand / afterCommand hook. Commands are intercepted via a browser proxy wrapper instead.
Limited test contextbrowser.currentTest provides less metadata than the WDIO runner context; test names and file paths require additional heuristics.
Flat suite nestingNightwatch does not natively support multiply-nested describe blocks; the plugin reports a maximum of two levels.
Delayed result availabilityTest results are only finalised in afterEach, not available mid-test.
Screencast in polling mode onlyUnlike WDIO (CDP push via browser.getPuppeteer()) and Selenium (CDP push via driver.createCDPConnection), Nightwatch lacks a stable CDP escape hatch, so frames are captured by polling browser.takeScreenshot(). Works on every browser Nightwatch supports; small per-frame cost proportional to the polling interval.
Per-test trace slicing (BDD describe/it)The BDD interface fires the plugin's per-test hook once per module, so traceGranularity: 'test' collapses to one session-scoped slice. The exports-object (mocha-style) and Cucumber interfaces get real per-test slicing. See Per-test slicing.
Produce-only trace artifactsPer-test screenshot / video files are written to the trace output dir (and the manifest when emitArtifactsManifest: true) but not attached inline to Allure — Nightwatch has no live Allure attach API.

Overall feature parity with the WebdriverIO DevTools service is approximately 80-90%.

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