ZPL to PDF API.

Quick start

curl -X POST "https://blznworks.com/api/zpl/render?width=4&height=6&dpi=203" \
  --data-binary @labels.zpl -H "Content-Type: text/plain" -o labels.pdf

That's it: each ^XA … ^XZ block in labels.zpl becomes one page of labels.pdf, at 4 × 6 inches. Without a key you are on the free plan (5 labels per request, 50 per day per IP address).

Endpoint

POST https://blznworks.com/api/zpl/render

Query parameters

Body

• ZPL text (Content-Type: text/plain), UTF-8 or a single-byte code page, any number of labels.
• Or, with Pro, a zip of .zpl, .txt or .prn files (Content-Type: application/zip). Files are read in name order, so zero-pad numbers (001.zpl, 002.zpl).

Authentication

Optional. Send your Pro license key as Authorization: Bearer BLZN-XXXXX-… (or X-Api-Key). The same key works in the web tool. The API counts as one device of the license.

Responses

200 with the file (application/pdf, image/png or application/zip) and these headers:

format=json returns { ok, labels, previewed, warnings, images, plan, remaining, limit, resetsAt }, where images are base64 PNGs of up to 12 labels, as the web tool's preview shows. Only previewed labels count toward the quota. Use it for previews; use pdf or png for output.

Errors

Errors are JSON: { "ok": false, "error": "too_many_labels", "message": "…" }.

Examples

curl

# Free: one label, PNG at 300 dpi, 100 x 150 mm
curl -X POST "https://blznworks.com/api/zpl/render?width=100&height=150&unit=mm&dpi=300&format=png" \
  --data-binary "^XA^FO50,50^A0N,60,60^FDHello^FS^XZ" -o label.png

# Pro: a zip of many .zpl files to one PDF
curl -X POST "https://blznworks.com/api/zpl/render?width=4&height=6&dpi=203" \
  -H "Authorization: Bearer $BLZN_KEY" -H "Content-Type: application/zip" \
  --data-binary @labels.zip -o labels.pdf

C# (.NET 6+)

using System.Net.Http.Headers;

using var http = new HttpClient();
http.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", Environment.GetEnvironmentVariable("BLZN_KEY"));

var zpl = await File.ReadAllTextAsync("labels.zpl");
using var response = await http.PostAsync(
    "https://blznworks.com/api/zpl/render?width=4&height=6&dpi=203&format=pdf",
    new StringContent(zpl, System.Text.Encoding.UTF8, "text/plain"));

if (!response.IsSuccessStatusCode)
    throw new Exception(await response.Content.ReadAsStringAsync()); // {"ok":false,"error":"…","message":"…"}

await File.WriteAllBytesAsync("labels.pdf", await response.Content.ReadAsByteArrayAsync());
Console.WriteLine($"Labels: {response.Headers.GetValues("X-Label-Count").First()}, left: {response.Headers.GetValues("X-Labels-Remaining").First()}");

JavaScript (Node 18+ or the browser)

import { readFile, writeFile } from "node:fs/promises";

const zpl = await readFile("labels.zpl", "utf8");
const response = await fetch("https://blznworks.com/api/zpl/render?width=4&height=6&dpi=203&format=pdf", {
  method: "POST",
  headers: { "Content-Type": "text/plain", Authorization: `Bearer ${process.env.BLZN_KEY}` },
  body: zpl,
});
if (!response.ok) throw new Error((await response.json()).message);
await writeFile("labels.pdf", Buffer.from(await response.arrayBuffer()));
console.log("labels:", response.headers.get("X-Label-Count"), "left:", response.headers.get("X-Labels-Remaining"));

The API sends Access-Control-Allow-Origin: * and reads no cookies, so it also works from a browser page. Never put a Pro key in public web pages: call the API from your server.

Plans and limits

Get a Pro key ↗

Current limits are also served as JSON at GET https://blznworks.com/api/zpl/limits.

Rendering notes

• Output is rendered at the chosen print density and placed on pages of the exact label size, so a PDF prints 1:1. Choose the dpi the ZPL was designed for: a 203 dpi label rendered at 300 dpi looks smaller.
• Supported: text and fonts (^A, ^CF, ^FB, ^FH, ^CI), boxes, lines, circles and ellipses, graphics (^GF, ~DG, ^XG, ^IM), stored formats (^DF/^XF), reverse print, and barcodes Code 128, Code 39, Code 93, EAN-13, UPC-A/E, Interleaved 2 of 5, Codabar, QR, Data Matrix, PDF417, Aztec and MaxiCode.
• Printer-only commands (^PQ copies, media, speed, darkness) do not change how a label looks and are ignored with a note.
• Privacy: the request body is held in memory while it is rendered and then discarded. Nothing is written to disk or logged except label counts for quotas.

Questions or a command that renders wrongly? Contact support with a sample label.