Shopify's cart attribute limit

Shopify's cart attribute limit is somewhere between 19.9 MB and 20 MB, or roughly: Max attribute value size ≈ 20,873,216 characters (just under 20 MB). To test this out use the script below on your Shopify store: 413...

By Joe Pichardo • April 19, 2025

Shopify’s cart attribute limit is somewhere between 19.9 MB and 20 MB, or roughly:

Max attribute value size ≈ 20,873,216 characters (just under 20 MB).

To test this out use the script below on your Shopify store:

413 (Payload Too Large) error will throw on the larger attribute.

const sizes = [
20873216, 20900000,21000000
];

(async () => {
for (const size of sizes) {
const largeString = 'x'.repeat(size);
const attributes = { long_data: largeString };

console.log(`🚀 Trying size: ${size} characters (${(size / 1024 / 1024).toFixed(2)} MB)`);

try {
const response = await fetch('/cart/update.js', {
method: 'POST',
headers: {
'Content-Type': 'application/json',
'Accept': 'application/json'
},
body: JSON.stringify({ attributes })
});

const data = await response.json();
const returnedLength = data.attributes?.long_data?.length || 0;

console.log(`✅ Size ${size}: Saved length = ${returnedLength}`);
} catch (err) {
console.error(`❌ Size ${size}: Cart update failed`, err);
}

await new Promise((res) => setTimeout(res, 1000)); // throttle-safe
}
})();

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