How this site works

A serial number, three regions, and one verdict.

The exploit

Fusée Gelée is a bug in the USB recovery mode (RCM) of the original Switch's Tegra X1 bootROM. It lets an attached PC push arbitrary code into the console before any signature checks run, which is what makes custom firmware possible. It's a hardware bug, not a software one — Nintendo couldn't patch it with a system update, so instead they revised the bootROM on the manufacturing line starting around mid-2018.

Consoles built before the revision are exploitable. Consoles built after it are not. Switch Lite and Switch OLED both launched with the revised board already in place, so every unit of either is patched. Later original-Switch units use a redesigned chip generation ("Mariko") that closes the bug at the hardware level the same way — serials starting XKW or XKJ are always patched.

From serial number to verdict

Nintendo doesn't publish which serial ranges got the revised bootROM, so the ranges below come from thousands of individual reports: someone tests their console with an RCM jig, posts the result and serial number, and over time the boundaries of each batch become clear. The checker looks at your serial's 4-character prefix plus the first 6 digits and places it against those boundaries.

Reading the regions

Each supported prefix has three regions, drawn as the ruler under your result:

• Not patched — below the boundary where revised units start appearing in that batch.
• Possibly patched — Nintendo didn't switch every production line over on the same day, so for a stretch of serials in each batch, both revised and unrevised units shipped mixed together. A serial in this range could be either; an RCM jig is the only way to know for sure.
• Patched — at and beyond the boundary where the batch had fully switched over.

Where the data comes from

All of it is community-collected on the GBATemp forums — not a proprietary database, just a spreadsheet a lot of people have contributed test results to over the years. We currently have usable ranges for eight prefixes: XAW1 XAW4 XAW7 XAJ1 XAJ4 XAJ7 XAK1 XAW9. If your prefix isn't in that list, it means your console is newer than anything in the data — which means it's patched.

We also don't store full serial numbers. The checker only ever sees the prefix and the first 6 digits you type or paste, and nothing is written to a database on our end.