Remove background from images in Node.js with the LassoCut API

Quickstart

Every request needs your key in the X-Api-Key header and exactly one image source. This example uses size=preview, which is covered by your account's 50 free previews a month (up to 10 a day). Node.js 18 or later has fetch and FormData built in, no packages to install.

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

const form = new FormData();
form.append("image_file", new Blob([await readFile("photo.jpg")]), "photo.jpg");
form.append("size", "preview");

const res = await fetch("https://api.lassocut.com/v1.0/removebg", {
  method: "POST",
  headers: { "X-Api-Key": process.env.LASSOCUT_API_KEY },
  body: form,
});
if (!res.ok) throw new Error(JSON.stringify(await res.json()));
console.log("credits charged:", res.headers.get("x-credits-charged"));
await writeFile("no-bg.png", Buffer.from(await res.arrayBuffer()));

Tested against the production API on 27 September 2026 with this exact request; it returned a valid PNG.

Run a folder with a promise pool of 3

Promise.all over every file would fire hundreds of uploads at once and hit the rate limit. A pool of three workers pulling from a shared index keeps exactly three requests in flight. Save it as cut.mjs (top-level await needs an ES module) and run node cut.mjs.

import { readdir, readFile, writeFile, mkdir, access } from "node:fs/promises";
import path from "node:path";

const API = "https://api.lassocut.com/v1.0/removebg";
const SRC = "photos", OUT = "out", PARALLEL = 3;
await mkdir(OUT, { recursive: true });

const exists = (p) => access(p).then(() => true, () => false);
const sleep = (s) => new Promise((r) => setTimeout(r, s * 1000));

async function cut(name) {
  const dest = path.join(OUT, path.parse(name).name + ".png");
  if (await exists(dest)) return `skip ${name}`;
  const bytes = await readFile(path.join(SRC, name));
  for (let attempt = 1; ; attempt++) {
    const form = new FormData();
    form.append("image_file", new Blob([bytes]), name);
    form.append("size", "full");
    form.append("format", "png");
    const res = await fetch(API, {
      method: "POST",
      headers: { "X-Api-Key": process.env.LASSOCUT_API_KEY },
      body: form,
    });
    if ((res.status === 429 || res.status === 503) && attempt < 5) {
      await res.body?.cancel();                  // free the connection
      await sleep(Number(res.headers.get("retry-after")) || 2 ** attempt);
      continue;
    }
    if (!res.ok) return `failed ${name}: ${res.status} ${await res.text()}`;
    await writeFile(dest, Buffer.from(await res.arrayBuffer()));
    return `ok ${name} (${res.headers.get("x-credits-charged")} credit)`;
  }
}

const files = (await readdir(SRC)).filter((f) => /\.(jpe?g|png|webp)$/i.test(f));
let next = 0;
async function worker() {
  while (next < files.length) {
    const name = files[next++];
    console.log(await cut(name).catch((e) => `failed ${name}: ${e.message}`));
  }
}
await Promise.all(Array.from({ length: PARALLEL }, worker));

• Retries: 429 Rate limit exceeded and 503 are retried up to four times. The wait comes from the Retry-After header, in seconds, or doubles from 2 seconds when it is missing. res.body?.cancel() releases the connection before waiting.
• Skip if done: an image whose out/<name>.png exists is not sent again, so a run stopped halfway, or by a 402 Insufficient credits, resumes where it left off.
• One failure does not stop the pool: each worker catches its own errors, prints the reason and moves on to the next file.
• Headers: x-credits-charged gives the cost of each call; x-ratelimit-remaining what is left of the 500 megapixel-images per minute.

The script was run on Node.js 22 against a local test server that answers 429 with Retry-After before succeeding; at most three requests were in flight at any time.

Point an existing Node.js client at LassoCut

Most Node.js remove.bg wrappers hardcode api.remove.bg internally and don't expose a base URL to change, so there is often nothing to reconfigure. The fetch example above is usually the fastest way to switch: it is a dozen lines with no dependency to audit.

If you use a generic HTTP client library that already sends this header and this multipart body to remove.bg (axios, undici, node-fetch), point its base URL at https://api.lassocut.com/v1.0 and keep the same X-Api-Key header; no other code changes are needed.

Useful options

Full list, including framing, shadows and background images: API reference.

Marketplace preset and shadow

A marketplace preset frames the cut-out on the canvas, white background and file size that marketplace expects, and shadow_type=cast adds a cast shadow. The response header X-Compliance says whether the result meets the rules LassoCut checks. With a preset, crop, crop_margin, scale and position are ignored. See marketplace presets.

const form = new FormData();
form.append("image_file", new Blob([await readFile("product.jpg")]), "product.jpg");
form.append("preset", "amazon");
form.append("shadow_type", "cast");
form.append("shadow_angle", "45");

const res = await fetch("https://api.lassocut.com/v1.0/removebg", {
  method: "POST",
  headers: { "X-Api-Key": process.env.LASSOCUT_API_KEY },
  body: form,
});
if (!res.ok) throw new Error(JSON.stringify(await res.json()));
console.log("compliance:", res.headers.get("x-compliance"));
await writeFile("amazon.jpg", Buffer.from(await res.arrayBuffer()));

Common errors

Errors return JSON: {"errors": [{"code": "…", "title": "…"}]}, available from await res.json() when res.ok is false. Nothing is charged on an error.

Full list: API reference.

Next steps

Read the full API reference for every parameter and header, or the migration guide if you're moving code that already calls remove.bg. No key yet? Create a free account, or try LassoCut on your image first, no key required.