What an Online Switch Tester Can and Cannot Measure
A browser receives 2 events per key, one when it goes down and one when it comes back up, and everything an online switch tester reports is derived from those two. That is enough to measure registration, repeats and timing to the millisecond, and it is not enough to measure what people actually choose switches for: a 45 gram spring and a 67 gram spring produce identical events, and so does a switch that clicks and one that does not.
Is a web page the same as a physical switch tester?
The confusion starts with the name. A physical switch tester is a small block holding four to nine loose switches, sold so you can press them and decide which one you like. It is not connected to anything and it measures nothing at all.
A web page called a switch tester is testing your assembled keyboard. It sees the finished output of a switch, a keycap, a matrix, a controller and a cable, and it cannot tell you which of those five produced the behavior on screen. When a key misbehaves, the page has shown you that something is wrong, not what.
What can a browser actually measure?
The measurable list is short and genuinely useful.
| Property | Measurable in a browser | How, or why not |
|---|---|---|
| Registration | yes | the key produces an event, or it does not |
| Physical position against character | yes | KeyboardEvent.code gives the location, KeyboardEvent.key the character |
| Double presses | yes | a key going down again under 15 ms after its own release |
| Auto repeat | yes | the browser sets a repeat flag, and our test discards those events |
| Simultaneous keys | yes | count of keys held together, which exposes the rollover ceiling |
| Actuation force in grams | no | the controller reports a closed circuit, not the pressure that closed it |
| Travel and actuation point | no | the event arrives at contact, with no depth attached |
| Sound and tactility | no | outside the channel entirely |
| Switch type | no | any page naming it is reading what you typed or guessing from the device name |
| Polling rate in hertz | no | browser timing covers the whole chain, not the keyboard alone |
The first five cover the faults that matter in daily use: a key that does not fire, a key that fires twice, a key the system reads as a different key, and a combination the board refuses. The threshold for the third row is deliberately low. A fast human repeat of the same key lands around 40 to 50 milliseconds, while contact bounce in a worn switch runs in single milliseconds, so 15 milliseconds sits cleanly between them.
What can no web page measure?
Force is invisible to software. The controller reports a closed circuit, not the pressure that closed it, so spring weight leaves no trace in the data. No page can tell a light switch from a heavy one, and a page that names a weight is repeating something it was told.
Travel and actuation point are equally hidden. The event arrives at the moment the contact closes, and how far down the stem that happened, whether at 1.2 mm or 2 mm, is not in the data. A page claiming to measure actuation depth from a browser is describing something it cannot see.
Sound and feel are outside the channel altogether. A tactile bump, the pitch of a bottom out, the difference between a lubricated switch and a dry one, the sound of the case: none of it reaches the browser. Nor does switch type. A page that names your switches is reading a claim you typed into it, or guessing from the device name the operating system reported.
Two further gaps are worth naming. Latency measured in a browser includes the operating system, the browser itself and the display, so it is a figure for the whole chain rather than for the switch. And durability, the rating printed on a datasheet in tens of millions of presses, is a manufacturing claim that no session of any length can confirm.
How do you use each tool for its own job?
Buy on the properties a web page cannot see, and verify with the properties it can. Feel, weight and sound come from pressing real switches, borrowing a colleague’s board, or reading a review that used a force curve machine. Registration, repeats and rollover come from the keyboard test, which is also where a second hand board should be checked before money changes hands.
That sequence catches the two common mistakes. One is choosing switches from a description of sound written by a shop. The other is concluding a board is faulty from a page that only reads characters and therefore misreports every key that produces nothing on its own, including the dead keys that European layouts rely on. A key that seems sluggish rather than broken is often just dirty, and cleaning it is the cheaper experiment.
Once the hardware checks out, the useful test is a real one: does the board stay pleasant for a few hundred words? Sonnet 33 answers that nicely. William Shakespeare saw it printed with the rest of the sequence in 1609, and its 338 characters end six lines out of eight in punctuation, which tells you more about a keyboard than any specification sheet does. John Keats gives the longer answer: To Autumn, printed in 1820, holds 494 characters together with semicolons, so the little fingers stay busy from the first line to the last. And The Village Blacksmith, which Henry Wadsworth Longfellow published in 1841, keeps a short regular line and a steady beat across 371 characters, which is the pleasantest way to listen to a board you are still deciding about. All three are waiting in the typing test, each with its author, year and source on its own page.
Who should use an online tester, and for what
Yes, use one to answer a hardware question with a yes or no: does this key fire, does it fire twice, does the board refuse this combination, is this second hand keyboard worth the money. Those are exactly the questions the two events per key can settle.
No, do not use one to choose between switches. Feel, weight and sound are the properties people actually buy on, and all three are invisible to software. A page that names your switch type is repeating something you typed into it, or guessing from the device name the operating system reported.
Where to start: press every key once in the keyboard test, then work through the list of positions that never lit. After that, hold several keys together for rollover, then tap a suspect key twenty or thirty times for doubles. Three actions, three different faults.
When the reading is not about the switch
- When the number is latency. Browser timing includes the operating system, the browser and the display, so it describes the whole chain. It is a useful figure for what you see, not a measurement of the keyboard.
- When the claim is durability. A rating in tens of millions of presses is a manufacturing claim, and no session of any length confirms it.
- When the key is meant to produce nothing. Dead keys wait for a second press before printing. A page that reads characters rather than key events reports every one of them as faulty.
- When the fault could be dirt. A key that feels sluggish rather than broken is often just contaminated, and cleaning it is the cheaper experiment than a replacement switch.
FAQ
Can an online tester tell me which switches I have?
No. Nothing in the event data identifies a switch, so a page that names yours is reading a value you selected or guessing from the device name the operating system reported. Force, travel, sound and tactility all leave the browser with nothing to read.
Is a physical switch tester the same thing?
No, and the shared name causes most of the confusion. A physical switch tester is a small block holding four to nine loose switches, sold so you can press them and pick one. It connects to nothing and measures nothing. A web page called a switch tester is examining your assembled keyboard.
If a key misbehaves, does the test tell me which part is faulty?
No. The page sees the finished output of a switch, a keycap, a matrix, a controller and a cable, and it cannot separate the five. It shows you that something is wrong, not what. Cleaning first is the cheap way to eliminate the most common cause.
How does the test avoid confusing auto repeat with a broken switch?
The browser sets a repeat flag on events generated by a held key, and the test discards every event carrying it before counting anything. What remains is a genuine second press, and only one arriving under 15 milliseconds after that key’s own release is reported as a double.
What should I check before buying a second hand keyboard?
Registration on every position, doubles on the keys with the most visible wear, and rollover on the combinations you actually use. Buy on feel, weight and sound, which the page cannot see, and verify on registration, repeats and rollover, which it can.
