Use case · Shipping labels
The shipping label PDF API
Warehouse printers expect an exact canvas — usually 4x6 inches — with the barcode positioned to the millimetre. Get the page size wrong and every label prints scaled, skewed, or off the edge of the roll.
Set explicit width and height instead of a paper format, inline the barcode as SVG, and you get a label that drops straight onto a thermal printer at full resolution.
01How it works
Exact 4x6 canvas
Explicit width and height options produce a page sized to the label stock, not a letter page with a label floating on it.
Barcodes that scan
Inline SVG barcodes render as vectors, so they stay crisp at 203 or 300 dpi thermal resolution.
Label plus packing slip
Render both documents and merge them into a single file with the merge endpoint, on the same API key.
02One request
curl https://rendral.com/api/v1/pdf \
-H "Authorization: Bearer sk_live_…" \
-H "Content-Type: application/json" \
-d '{ "html": "<div class="label"><svg class="code128">…</svg></div>",
"options": { "width": "4in", "height": "6in",
"margin": { "top": "0", "bottom": "0" },
"printBackground": true } }' \
-o label-1Z999.pdfFrequently asked
How do I get exactly 4x6 inches?
Set width: "4in" and height: "6in" and zero the margins. Don't use a named format like A4 — the label will be scaled to fit the paper instead.
Will barcodes scan reliably?
Yes, if they're vectors. Inline the barcode as SVG rather than a raster image so it stays sharp at thermal-printer resolution.
Can I combine the label and the packing slip?
Render each one, then POST both to /api/v1/merge to get a single PDF — the same key covers both endpoints.
Does this work with ZPL printers?
This produces PDF, which most modern label printers and print servers accept. If your workflow is strictly ZPL, keep generating ZPL — PDF is the better fit when you want the same design on screen and paper.
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