Slack's marketplace, read without a browser: 2,690 apps, 6,792 category memberships, and a page parameter that is really an offset

The Slack Marketplace is the second marketplace the Atlas will cover. On 10 September 2026 we read it with a plain HTTP client and no browser. The snapshots are Research/slack-marketplace-sitemap-2026-09-10.csv, …-categories-2026-09-10.csv, …-apps-2026-09-10.csv and …-memberships-2026-09-10.csv.

What is there

• robots.txt publishes a marketplace sitemap with about 2,700 listing URLs. Its category URLs are stale; the live shape is /marketplace/category/<id>-<slug>.
• Category pages are server-rendered and carry a JSON blob in #props_node[data-props]: the total apps found, the apps in popularity order, 25 per request, a pricing enum, a directory-approval flag, and every category each app belongs to.
• ?page=N is a zero-based item offset, not a page number: walk a category at 0, 25, 50 and so on. The order is stable across requests. ?sort=name is alphabetical; ?price=<enum> filters with exact totals; ?sort=newest is ignored.
• The full pass captured 2,690 apps and 6,792 category memberships. The sitemap and the category pages disagree at the edges — 12 listings in one and not the other, 2 the other way.
• The Wayback Machine holds category captures back to January 2025 with the same blob, so a history is possible.

What is not there

No install counts, no ratings, no prices beyond the enum. Listing pages are text only: scopes and a security block. /marketplace/agents is behind a login. Identifying ourselves in the user agent changed nothing.

What it means for the adapter

Crawlee, not a browser. Categories as the unit of collection, popularity rank as the only demand signal, and no invented install or revenue figures — the Slack report will say what the marketplace does not expose, as the Apify one does.