How much proxy traffic a browser profile uses

How much proxy traffic you need comes down to what your profiles load. The number of profiles in the library hardly matters. A browser fetches every script, font, image and video segment a page names, and an order dashboard and a video feed are not in the same league. So measure one real profile for a week, then multiply by the profiles you open.

We won't print a table here, because every one we have seen, ours included, is a guess set in a confident font. In what a proxy costs per profile per month we used 0.5 GB and 3 GB a month as round assumptions and said so on the page. Your own figure will be different, and it takes a week to get.

What the seller's meter counts

A per-GB residential plan counts the bytes that pass through the seller's gateway. That covers a lot more than the article or dashboard you had in front of you:

• the page itself, and every script, stylesheet, font and image it asks for
• video and audio segments, which on a feed with autoplay are most of the total
• ad frames, analytics beacons and tag managers, each fetching their own files
• API calls a dashboard makes while it sits open, polling for new orders or messages
• the TLS handshake and headers on every new connection
• whatever the browser fetches for itself in the background

The fourth and the last are the ones nobody counts. Leave a shop's orders dashboard open and it can keep asking its server about new orders all afternoon, so a tab you "only opened once" is a slow drip on the meter. And Chrome opens connections before you ask for anything. A restored tab preconnects to its own site during start-up; we learned that when a proxy counter of ours was reset too late, and the story is in Chrome preconnected before we started measuring.

Sellers differ on rounding, on whether upload counts, and on whether a failed connection is billed. Those are written on each seller's own pricing or help page, and that page beats any forum thread.

How it works: Provider minting

Why a profile is not your everyday browser

Your own browser has a warm cache. The logo, the fonts and the big script bundle of a site you visit daily were downloaded weeks ago and are read from disk. A separate browser profile has a separate cache, so its first visit to every site downloads all of it again, through the proxy.

That has three consequences for a profile library:

1. A new profile is at its most expensive in its first days, while its cache fills.
2. Clearing a profile's cache resets it to that state. Mosaic has a Clear cache action, per profile and in bulk, and the next visit after it pays full price.
3. Ten profiles on the same site each download that site once. Separate caches are part of keeping profiles apart, so the cost is the point, not a fault.

Warm-up counts too. Mosaic's warm-up robot browses a profile in its own browser, with its own proxy, so it has history and cookies before the site that matters sees it. Every page in a warm-up plan goes through that profile's exit and onto the same bill. Mosaic's check of a proxy before each launch also goes through the proxy, which is small next to a page load but not zero.

How to measure one profile

The test profile should be an ordinary one, opened on the sites the others will open, at the hours they will be open. There are three places to read its bytes and each answers a different question.

DevTools, for one page

Open DevTools on the Network tab before the page loads (Cmd+Option+I on a Mac, F12 on Windows), then load it. At the bottom you get two figures, transferred and resources. Transferred is the compressed size that came over the wire, and that is what a seller meters. Resources is what those bytes unpack to, which is why it is usually the larger number.

Then tick Disable cache and reload: that is a cold visit, which is what a new profile pays. Untick the box and reload once more for the warm figure. The gap between those two readings is the extra a profile costs in its first week.

DevTools only counts the tab it is attached to, and only while it is open. Use it to find out which page is expensive. Don't use it for a week's total.

chrome://net-export, for the whole browser

chrome://net-export writes every network event to a JSON file: all tabs, plus whatever the browser does on its own. Leave the privacy option on its default, which strips cookies and credentials, start logging, browse for an hour, and stop. The file opens in Chromium's NetLog viewer. Reading it is slow work next to DevTools, but it is the only one of the three that shows you requests no tab asked for.

The seller's usage page, for the bill

Your bill comes from the seller's meter, so that is the number to trust. A week of the test profile running alone gives a clean reading, and a sub-user or separate plan keeps it apart if your seller offers either. Day eight's usage minus day one's, over seven, is a day. Thirty of those is a month.

Mosaic can also put an inspector in the path, for when the question is which requests make up that number. Settings › Network routes every launch through Proxyman, Charles, mitmproxy, Fiddler or Burp; each request shows up there with its size, and the profile still browses from its own exit.

How much proxy traffic you need, from one profile to a plan

From one profile's figure to a plan is four lines of arithmetic:

1. Take one profile's measured month.
2. Multiply by the profiles you open in a month. Leave out the ones that sit in the library unopened, because they move no bytes.
3. Add the warm-up runs you have planned for new profiles. They go out through the same exits.
4. Add a margin. A site that ships a new script bundle makes every profile download it again, cold.

As a worked example, and not a forecast, take the two round assumptions from the cost post: twenty profiles at 0.5 GB is 10 GB a month, and the same twenty at 3 GB is 60.

Too much? Closing the tabs nobody is reading helps most with dashboards, since those poll. Clear a profile's cache only when you mean to start it over. Video feeds belong in the profiles whose work is video. Putting several profiles behind one exit would fit a cheaper plan too, at a price: every site then logs those profiles arriving from one address. Forty profiles on forty exits is the long version of that warning.

Mosaic doesn't sell proxy traffic, so the plan you sized is bought from your own seller. Paste one of its gateway lines into Mosaic as a provider and every profile mints its own session on that plan.