Storage Speed Test

A browser cannot test your disk

This needs saying before anything else, because plenty of sites claim otherwise. A web page has no access to your file system, your drive, or any interface that would let it measure them. There is no API for it, by design.

What this page measures is IndexedDB write and read throughput: how fast the browser can store and retrieve data in its own sandboxed database. That does eventually reach your drive, which is why the number is not meaningless — but a great deal sits in between.

• The browser buffers writes. A write that returns instantly may not have reached the drive yet.
• Reads usually come from cache, which is why the read figure is often absurdly high and should be ignored.
• The browser adds its own overhead — serialisation, transaction handling, quota accounting.
• Private browsing changes everything, and often keeps storage in memory entirely.

So: useful for comparing browsers, or for noticing that storage has become dramatically slower than it was. Useless as a drive benchmark. For that you need a native tool such as CrystalDiskMark, or the built-in utilities on macOS and Linux.

Why the read figure looks impossible

If reading back shows thousands of megabytes per second, the data never left memory. That is the browser's cache doing its job, not your drive being extraordinary.

How to use it

1. Close other tabs and applications first. This matters more than anything else you can control.
2. Plug the laptop in if it is on battery. Power saving changes the result substantially.
3. Press run and leave the tab in the foreground — browsers throttle background tabs.
4. Run it three times and use the best. Write speed is the only figure worth reading.

Common uses and tips

• Comparing browsers, which differ substantially in IndexedDB performance.
• Checking whether storage has degraded, for instance on a nearly full drive.
• Confirming storage works at all — a failure here usually means private browsing or a blocked-storage setting.
• Not for benchmarking an SSD. Use a native tool.

The test writes 24 MB, reads it back, and then deletes its database entirely. Nothing is left behind.

Questions people ask

Can a website test my disk speed?

No. A web page has no access to your file system or drive. This measures IndexedDB throughput, which reaches the drive eventually but through a great deal of buffering.

Why is the read speed so high?

Because the data is being served from memory cache rather than from the drive. Ignore the read figure.

Does this leave anything on my computer?

No. The test database is deleted as soon as the measurement finishes.

What should I use to benchmark an SSD?

A native tool such as CrystalDiskMark on Windows, or the disk utilities built into macOS and Linux.

The test says storage is blocked.

Usually private browsing, which often keeps IndexedDB in memory or disables it entirely.