Why Open VSX download counts look inflated

Publishers who dual-list often notice the Open VSX number is an order of magnitude above the Marketplace one and assume Open VSX is “winning.” Sometimes it is. Often it is just counting different events.

What each registry actually increments

VS Code Marketplace exposes two counters:

• install — unique installs
• updateCount — update events

Open VSX exposes one: downloadCount. It increments on every version download, including updates. A single machine that installs an extension and then takes ten updates contributes ten to downloadCount. There is no unique-install or active-install metric anywhere in the Open VSX API.

That is why the same extension, on 5 September 2026, showed 108,489 downloads on Open VSX against 10,476 unique installs on the Marketplace. The two numbers measure different things. The Open VSX figure is inflated by release frequency.

VSXRank stores Open VSX downloadCount in the downloads column and leaves the Marketplace-only installs column null on those rows. The UI label is Downloads. Never “installs.”

What that does to a chart

From the first two days of our crawl, 18 hours apart:

• Marketplace: 84% of extensions did not move. The median mover gained a handful of unique installs.
• Open VSX: only 5% were unchanged. Anthropic.claude-code jumped +131k downloads in a day; another extension jumped 21% in a day.

Those spikes line up with release days, because every auto-update of every already-installed copy is another download. An extension that ships weekly will look far larger than one that ships twice a year, at equal real user counts.

Compare Open VSX only in percentages or period-over-period deltas. Never add that counter to the Marketplace unique-install figure. Never rank the two registries in one table by the raw counter. Our category boards and the landing feed are split for this reason; the September catalog report uses the same split.

Practical rules

1. If you ship often, expect Open VSX to look “ahead.” That is the counter working as designed, not a hidden audience 10× the Marketplace.
2. If you ship rarely, Open VSX will look “behind” even when Cursor users have you installed. Do not use that gap as a reason to ignore the registry. Publish to it anyway.
3. A vertical jump on the Open VSX chart after you tag a release is a health check (“the new version is being pulled”), not a launch-day user count.
4. Marketplace unique installs are the slow, honest line. Use them for “are we growing.” Use Open VSX deltas for “did this release actually roll out on the other editors.”

We crawl Open VSX every four hours because those release spikes are real and short. The Marketplace stays on a nightly cadence because unique installs at small scale are not even monotonic hour to hour — an extra point would be noise.