Engine versions

The engine improves with each release: a law of the spec kept more closely, a layout more like a browser's. A document that depends on how it printed before can keep printing that way while you check it with the new engine.

Which engine printed it#

Every print says it: ReflowPDF-Engine: af4ba3e3b beside the file, engine in the JSON (a job's result too); a merge, split or compress says it when a part of it was printed in the same request. GET /v1/engines lists the versions that print now:

{
  "object": "list",
  "has_more": false,
  "data": [
    {
      "object": "engine",
      "version": "af4ba3e3b",
      "status": "current",
      "available_until": null
    },
    {
      "object": "engine",
      "version": "866470307",
      "status": "previous",
      "superseded_at": "2026-11-01T06:13:22.000Z",
      "available_until": "2026-12-01T06:13:22.000Z"
    }
  ]
}

Pin a print#

curl https://api.reflowpdf.com/v1/pdf \
  -H "Authorization: Bearer $REFLOWPDF_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"html": "<h1>Q3</h1>", "engine": "866470307"}' -o q3.pdf

const pdf = await reflow.pdf.create({ html, engine: '866470307' })

pdf = client.pdf.create(html=html, engine="866470307")

• engine goes on any request that prints: HTML, a template, images, the layout, a job, a part of a merge.
• When a release brings a new engine, the one before keeps printing until three newer engines have shipped, and for 30 days at most: available_until is that latest moment. Engines ship often, sometimes several in a week, so a pinned version can end well before it.
• A version that prints no more answers 422 engine_unavailable, naming the ones that do. Without engine, the current engine prints.
• A pinned version is the engine as it was: it gets no fixes. Pin it while you check your documents with the current engine (ReflowPDF-Engine says which printed), then leave engine out.