DevTools in session replays

• Which sessions this week had a JS error? You can watch the ones that broke, not a random sample.
• A customer says the dashboard is slow. Did the main content paint in 1 second or in 6?

On websites, Sequential's recorder captures JS errors, console output, network requests and page performance with each recording. Each is a capture that you turn on or off per project. All four are on by default.

• Sequential stores only what the settings allow. When a recording arrives, Sequential applies the project's current DevTools settings, whatever the page sent.
• Sequential counts only what it stored. It counts the JS errors and failed requests in the stored data. So the Sessions list never counts something that the replay cannot show you.
• Errors that your analytics SDK reports itself also show in the DevTools drawer. An example is a PostHog exception event. The drawer marks these via PostHog. The Sessions list does not count them.

If the session had problems, the badge on the </> DevTools button shows them. For example: "2 exceptions" or "1 failed".

If you click a JS error or a failed request on the timeline, the drawer opens on that entry. A link that you copy with Share opens the drawer again on the same tab. For what each tab shows, see Each tab in detail, below.

What the badges count:

• JS errors are uncaught exceptions and unhandled promise rejections that Sequential's recorder caught. They also include errors reported through the Smartlook compatibility script. See Moving from Smartlook.
• console.error calls are not in this count. The drawer counts them separately.
• A failed request is a fetch or XHR call that returned HTTP 400 or above. On websites, a call that ended in a network error or a timeout has also failed, also when the tab was in the background.
• A call that the browser cancelled because the user left the page has not failed. Neither has a prefetch, which is a request that the page sends before the user needs it. This applies to sessions recorded from 13 October 2026. Before that day, the recorder could not tell a cancel when the user left the page from a network error.
• To see the definitions, hover over the Problems cell. They show when the DevTools counts found a problem.

How the filters work:

• If both filters are on, a session must match both.
• Latest loads 100 sessions at a time. Sequential applies the filter before it splits the list into pages. So the filter finds broken sessions anywhere in the date range.

A badge names problems only. For each kind of problem, a session is in one of three states. Two of them show no DevTools badge.

The difference is important when a filter is on. The list shows a note with the number of recorded sessions in the date range that it could not check. These notes ignore your other filters:

• "N sessions in this range weren't checked for DevTools signals." These sessions are not measured.
• "N sessions in this range couldn't be checked for this filter (that capture was off, or wasn't reported)." These sessions are not captured.

Not captured

• On websites, the recording did not report that kind. Usually that capture was off for your project.
• A website recording with no DevTools data at all is also in this state once Sequential counts it. An example is a recording made before DevTools existed.
• On mobile, your app's SDK did not report that kind.
• A mobile session with no observed failed request is also in this state. Sequential cannot see a request that got no response.

Not measured

• Sequential has no counts for the session. Sequential counts each part of a recording when the part arrives, so this does not happen to a recording that the current server stored.

A zero reads as "nothing went wrong". If unchecked sessions counted as zero, With JS errors would silently drop every older broken session. The list would then call those sessions clean.

The AI judge behind Watch and Ask reads these counts too. Sequential never tells the judge zero for something it did not count.

If Sequential counted only part of a session and N is above zero, it tells the judge "at least N". So Watch can rank a session for its errors while its row on Latest shows no badge.

Whatever the settings, Sequential replaces some values with [redacted] in DevTools data. This redaction catches only known formats. It is not a guarantee. See What Sequential redacts, below, and Masking and redaction.

Console

• Each row shows the time, the level, the message and where the app logged it, such as cart.js:42.
• To filter, use the level chips Errors, Warnings, Info, Logs and Debug.
• To search, use Filter console.
• To see a row's kind, full text, arguments and stack trace, click the row.
• On an exception or an error-level row, the detail has Ask your agent. It hands a prompt about that error to a coding agent on your computer. See Find and replay sessions.

The kinds are:

• Uncaught exception
• Unhandled promise rejection
• Custom error, for an error sent through the Smartlook compatibility script
• a console call
• Reported by PostHog

If an error reads only Script error., the browser hid its details, because the script comes from another origin. To see the details, add crossorigin="anonymous" to the script tag. Then serve the script with CORS headers.

Network

Each row is one request, with Method, Status, Name, Type, Size and Duration. A status can be, for example, "404 Not Found" or "Timed out". On websites, these statuses are also possible:

• "Cancelled (page left)": the browser cancelled the request because the user left the page. This is not a failure.

• "Failed (background tab)": the request failed while the tab was in the background. This is a failure.

• A prefetch has "(prefetch)" after its name. A prefetch is never a failure.

• Failed only shows only the failed requests.

• The type selector shows one type, such as Fetch/XHR or Document.

• Filter requests searches the URLs. Under Strict, the path of a file that the page loads is masked, so you cannot search for its file name.

• In the detail of a request, a query value that Sequential did not keep reads "value not recorded".

Aborted requests, requests cancelled because the user left the page, prefetches, and failed assets, such as images and scripts, do not count as failed requests.

Performance

• The tab shows one card per full page load.
• It does not measure navigations inside a single-page app separately.
• Each card shows the Core Web Vitals LCP, INP, CLS, FCP and TTFB. Each is rated Good, Needs work or Poor.
• To see the cut-offs, hover over the name of a vital.
• A vital that the page never reported reads Not reported.
• Below the vitals, a bar splits the load into DNS, Connect, Request, Response, DOM and Load.

Whatever the settings, Sequential replaces these values with [redacted] in DevTools data:

• JWTs, and Bearer and Basic credentials
• email addresses
• card numbers that pass a Luhn check
• values logged under key names such as token, password or secret

On websites, Sequential does this before anything leaves the browser, and again on the server. See Masking and redaction.

The Attribute text masking setting also changes the addresses in DevTools. Strict uses Strict. Balanced uses Off. The recorder applies the rule in the browser, and Sequential's servers apply it again under the project's current setting.

• A request with no kind, or a kind that Sequential does not know, counts as a file.
• Keep query values for applies to network requests only. In every setting, query parameter names stay, and addresses lose the #fragment and any user:pass@.
• Under Strict and URLs, a query item with no =, such as ?<uuid>, becomes [redacted].
• A segment is id-like when it holds a UUID, a hex run of 16 or more characters or an email address anywhere, such as <uuid>.json. Masking and redaction gives the full rule.
• The text rule reads each word that holds a /, and masks only what comes after the first /. Prose such as and/or, 2026/09/29 and v1/2 stays as it is.

What Strict does not mask in DevTools:

• Domain names, and query parameter names.
• Numbers of 5 digits or fewer, and name slugs, in the route of an API call.
• An id in text with no / before it in its word, such as id=<uuid>. The keys of a logged object.

Under Strict, you cannot see which file failed to load. A failed image, script or font shows only its domain, its kind, its status and its timing. To find the file, reproduce the issue in a browser, or use Attribute text set to URLs on a staging project.

While text is off, console rows read like console.log at cart.js:42. With text on, you also see the words that your app logged, such as "payment failed: card_declined". This is the difference between knowing that console.error fired and knowing why.

Exceptions keep their message either way. There is one case where this is not true: a promise rejected with a plain object, not an Error or a string. While text is off, that rejection reads only as its type, such as Unhandled rejection: [object Object].

Redaction catches formats, not meaning. For example, Sequential does not redact console.log("reset link for", user, "is", url). It also does not redact names, addresses, one-time links, custom tokens or logged API responses.

• Turn text on freely in a staging or development project.
• In production, turn it on only after you check what your app logs.
• Settings are per project. So you can turn text on in a staging project and keep it off in a production project.

While text is off, Sequential empties message text as it arrives. This includes text from an older recorder, or from a mobile SDK that sends it. Text that is already stored stays in the recording. Sequential cannot remove it. See Retention and deletion.

• Other roles see the form read-only, with "Ask an owner or admin to change this."
• In the DevTools group, the settings are JavaScript errors, Console and its levels, Record message text, Network requests and Performance.
• The DevTools group is one setting, shared by the Web, iOS and Android tabs.
• On the mobile tabs, JavaScript errors and Performance are greyed out and marked "Web only."
• A pattern matches the whole URL, scheme and host included, but not the query. So write https://api.example.com/health or **/health, not /health.
• In a pattern, * stays within a path segment. ** crosses path segments.
• These changes record more than before, so they open the Loosen masking? sheet:
  • errors, console or network capture turned on
  • a level added
  • message text turned on
  • a query value kept
  • a request pattern removed

Sequential applies your current settings to every upload as it arrives. So when you turn a capture off, Sequential stops storing that data immediately. Websites use the change on their next page load. Mobile apps use it on their next launch. See Recording settings.

iOS and Android recordings come from PostHog's mobile SDKs. See Mobile apps.

• The Performance tab reads "Performance metrics are recorded for websites."
• Every mobile log counts as console output, never as an exception. So mobile sessions never match With JS errors. With that filter on, the list counts them in its notes.
• On mobile, a request counts as failed only when it returned HTTP 400 or above. Sequential cannot see a request that got no response, such as a timeout or no connection. No setting changes that.
• So a mobile session with no observed failure does not match With failed requests, and the real number of failed requests can be higher than the count.
• The replay cannot tell an SDK that sent nothing from a capture that was off. The empty tab says this.

Logs

• Native iOS apps must also set captureLogs: true.
• Android sends logcat by default.
• In React Native, captureLog is on by default.
• The Flutter SDK does not send logs.

Network requests

• iOS sends requests from URLSession by default.
• Android needs PostHogOkHttpInterceptor.
• React Native sends requests on iOS only.
• Flutter sends none.

Requests with no response

Mobile SDKs send request metrics only. Sequential cannot see a request that got no response at all, such as a timeout or no connection. PostHog's mobile SDKs do not report it, and no setting changes that.

So a mobile session with no observed failure is "couldn't be checked", never "0 failed requests". It shows no badge for it. It does not match With failed requests. The list counts it in its note.

• The list counts every occurrence of an error that Sequential's recorder caught.
• The header counts each drawer row once. This includes errors that PostHog reported.
• An error that repeats quickly is one drawer row, marked ×N.

So a header's "3 exceptions" can show beside a row's "2 JS errors". Or "1 exception", one row marked ×5, can show beside "5 JS errors".

The Insights tab judges the session from its events. It does not see the DevTools counts. So for a session that broke, its answer can differ from the answer in Watch. See Session insights.