Internet Simulator

What happens when you type a web address and press Enter?

Beginner10 minSimulated

Words you’ll meet:

DNS
TCP/IP
SSL/TLS
HTTP
CDN
Load Balancers

A browser that has never seen this site: a full DNS walk, a TCP handshake, a full TLS handshake, and only then the page and everything it asks for.

How much of a page load happens before the request has even been sent
Why a render-blocking stylesheet decides when the first frame appears
That the largest contentful paint carries the cost of every stage before it

8 steps. Pause, step back or replay any of them.

Press Play to watch it happen, in 8 steps.

Steps

Before anything is sent, the browser splits the address into the pieces each later stage needs: the host for DNS, the port for the connection, and the path for the request.
Three checks happen before any packet exists: the HSTS list, the service worker, and the browser’s own cache. Each one can make the rest of the page load unnecessary.
The browser asks its resolver, which walks down from the root: the root refers it to the TLD servers, they refer it to the zone’s own servers, and only the last of those actually knows the address.
Three segments, one round trip, and not one byte the user asked for. Both ends agree they exist, agree where each other’s numbering starts, and only then may anything be sent.
Two questions at once: what key protects this connection, and is the far end really the host that was typed. The second is the certificate’s whole job.
91 bytes, 0.01 ms to clock onto the wire, and 12.5 ms to get there. Everything before this stage was preparation.
The origin has the request. Everything from here until the first byte arrives is the server’s own time.
The document is the beginning of the page load, not the end of it. Every stylesheet, script, font, and image it names is another request -- and the first frame cannot be painted until the ones that block it have arrived.

Details

Nothing selected

Click anything on the map (a device, a cable, or a moving message) to see what it is.

Step 1 of 8

0 ms438 ms

Stage rail

438 ms total · Render is 35% of it

Widths are each stage’s real share of the run, with a floor so a fifth-of-a-millisecond stage stays clickable. Hatched segments took no time: they were skipped, or the run ended before them. Pick one to open it.

Viewport

Blank

https://www.example.com/

Nothing painted yet

The document has not arrived. Everything happening on the rail above is happening behind an empty frame.

FP 347 msLCP 378 ms

TTFB: 277 ms
First Paint: 347 ms
LCP: 378 ms
Load: 370 ms
Transferred: 373.0 kB
Requests: 6 network, 0 cached

Network profile

A typical wired home connection: 25 ms out and back, and plenty of capacity.

Satellite carries more bandwidth than 3G and still loses badly. A page load is mostly round trips, and no amount of capacity shortens one -- which is the entire reason TLS 1.3, session resumption, HTTP/2, and connection reuse exist.

Network waterfall

6 requests · 370 ms

Every request this page load made, with the standard browser devtools timing segments.
Name	Size	Time
document · 200	33.5 kB	283 ms
stylesheet · 200	41.3 kB	54 ms
script · 200	93.8 kB	71 ms
font · 200	27.4 kB	47 ms
image · 200	175.8 kB	85 ms
fetch · 200	1.2 kB	56 ms

First Paint 347 ms

LCP 378 ms

Queueing
DNS Lookup
Initial connection
SSL
Request sent
Waiting (TTFB)
Content Download

These are Chrome’s own segment names. Subresource rows carry no DNS Lookup, Initial connection or SSL because the document already paid for all three, and they reuse its connection — which is most of what connection reuse is worth.

Everything that happened3 / 107

The map as a list

6 machines, 5 links

Loading the simulation…

Internet Simulator

How to use this page

Steps

Details

Stage rail

Viewport

Network profile

Network waterfall

The map as a list

How to use this page

Steps

Details

Stage rail

Viewport

Network profile

Network waterfall

The map as a list