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Assets you upload live on usercontent.abtestly.com. Deliberately a separate hostname from app.abtestly.com and cdn.abtestly.com. customer content is isolated from the app and the snippet.

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The URL shape

  • <namespace>, a per-site 32-character hex string. Namespaces are isolated from each other; site A cannot enumerate site B’s files.
  • <hash>, the SHA-256 of the file contents. Content-addressed. any change to bytes produces a new URL.
  • <filename>, the canonical filename. A request with a different filename returns a 308 Permanent Redirect to the canonical one.

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Cache

Every response includes:
That is one year, marked immutable. Browsers cache aggressively; CDNs and edges cache aggressively. Safe, because the content is content-addressed, a change means a new URL. The old URL never serves different bytes.

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CORS

Access-Control-Allow-Origin: *. Assets are safe to reference from any domain. <img>, <video>, CSS background-image, <a href> for PDFs, all work anywhere.

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Content type

Set from the file’s sniffed type at upload, not from the URL extension. image/png, image/jpeg, image/gif, image/webp, application/pdf. HEAD /a/… returns the same headers as GET /a/… with no body. Useful for programmatic size checks.

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Rate limits

None on serving. The URL is a static-file URL cached at Cloudflare’s edge, traffic is essentially free for us. The upload endpoint on the dashboard side is rate-limited (100 requests per minute per user), but that only matters if you are batch-uploading.

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Takedown

Two ways an asset can stop serving:
  • You deleted it. Soft-delete first, then permanent-delete. See Recycle bin.
  • We took it down. Admin action, only in response to a legal request (DMCA, GDPR erasure) or an abuse report. When this happens, the R2 object is deleted and the URL is purged from Cloudflare cache within minutes.
If your file was taken down and you believe it was in error, email support with the URL.

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Why a separate hostname

Two reasons:
  • Cookie isolation. usercontent.abtestly.com shares no cookies with app.abtestly.com or cdn.abtestly.com. A malicious file (a crafted PDF with active content, for example) cannot read auth cookies.
  • Cache scope. Cache-Control headers for user content are different from the app and the snippet. Separating hostnames keeps the cache behavior clean.

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The Access-Control-Allow-Origin is deliberately wildcard

Some CDN products default to same-origin for user content. We do the opposite, user content should work inline anywhere the user pastes the URL. If your compliance policy needs a specific origin, tell us.
Last modified on August 1, 2026