Page Load Time Breakdown
Use the interactive waterfall chart to see the browser's exact execution sequence
and identify which phase accounted for most of the transaction time.
The Page Load Time Breakdown waterfall chart maps W3C
PerformanceNavigationTiming timestamps into a sequential visual timeline. Each row
represents a phase or sub-step in the browser's page load sequence. The chart
displays the absolute duration and its percentage of the total load time for each
step, together with a horizontal bar that shows when the step started and ended
relative to the full timeline.
The chart overlays vertical marker lines for DOM, FCP, and LCP
so that you can correlate technical timing events with the user-facing metrics shown
in the Web Vital Metrics section.
Select any bar to view a tooltip with start time, end time, and duration for that
step. Select a phase row to expand or collapse its sub-steps.
The waterfall progresses through the following phases in sequence:
PREPARE
Captures device-side delays that occurred before the browser could start the
network request. A significant PREPARE phase indicates that the browser
was occupied with other activity—such as servicing concurrent requests or
allocating cache space—before it could begin connecting to the server.
| Step | Description |
| Queuing | Time the request spent waiting in the browser's network
queue. The browser queues requests when it has reached the
maximum number of concurrent connections to the origin, when
higher-priority requests are pending, or when disk cache space is
being allocated. |
| Stalled | Time the request was stalled after it left the queue but
before the browser began sending data. Stalling occurs for
similar reasons to queuing and can also indicate overhead
introduced by a proxy or browser extension. |
CONNECT
Captures the time the browser spent establishing the network connection to the
server. A large CONNECT phase indicates a network infrastructure issue
such as slow DNS resolution, high round-trip latency, or a slow TLS handshake.
CONNECT is typically the largest phase on first visits to a domain
because the browser must establish a new connection rather than reusing an
existing one.
| Step | Description |
| DNS Lookup | Time to resolve the page domain to an IP address. A slow DNS
Lookup can indicate an overloaded or geographically distant DNS
resolver. If this step is consistently high, work with your
network team to investigate the DNS infrastructure. |
| TCP Connect | Time to complete the TCP three-way handshake between the
browser and the server. High TCP Connect times reflect network
round-trip latency between the user and the origin server and
are typically caused by geographic distance or network
congestion. |
| SSL/TLS |
Time to negotiate the encrypted session between the browser
and the server. In addition to start time, end time, and
duration, the tooltip for this step also shows:
|
RESPONSE
Captures the full server response time from when the browser sent the complete
request to when all response data was received (Time to Last Byte, TTLB). A
large RESPONSE phase indicates that the application server is slow to
process the request, the response payload is large, or the connection has
limited throughput.
| Step | Description |
| Waiting |
The time the browser waited for the server to begin returning
data after the request was sent (Time to First Byte, TTFB).
In addition to start time, end time, and duration, the
tooltip for this step also shows HTTP Version—The
application-layer protocol used for the connection, for
example, HTTP/1.1, HTTP/2, or
HTTP/3.
|
| Content Download | The time for the browser to receive the complete response
body after the first byte arrived. If Content Download is
disproportionately large compared to Waiting, the issue is
likely network throughput or payload size rather than server
processing. |
RENDER
Captures the client-side browser work that occurs after the HTML response has
been received. A large RENDER phase indicates that the page has
significant JavaScript execution, complex CSS, or a large number of sub-resources
to load. A large RENDER phase points to the application or the user's device as
the bottleneck rather than the network or server.
| Step | Description |
| DOM Processing | The time for the browser to parse the HTML response and build
the Document Object Model, including loading and executing any
render-blocking scripts. A long DOM Processing time indicates
heavy JavaScript execution or deeply nested HTML on the
page. |
| Page Load |
The time from when the DOM became interactive until the
browser fired the load event, indicating that all
dependent resources—images, stylesheets, and scripts—have
finished loading. In addition to start time, end time, and
duration, the tooltip for this step also shows Objects
Loaded—The number of objects that loaded successfully out of
the total number of objects the page attempted to load, for
example, 56/76 objects loaded. Use this count to
assess page weight and complexity when investigating slow
rendering without examining individual resources.
|