How much does a color-palette-extract call cost?

$0.003 per call, paid in USDC on Base via x402, with no account and no API key.

What does color-palette-extract return?

A JSON object with 6 top-level fields: source_url, source_format, sample_size, count, dominant and colors. The example on this page is a real call over images/palette-bands.png.

What happens when a color-palette-extract call fails?

The tool answers with a typed JSON error from the errors table. Payment is settled only after the tool has produced its result; a call that fails inside the tool is never settled. A 503 upstream_unavailable can follow a settled call; the x402 payments guide covers it, 429, 402 and an uncertain 500.

catalogue / tools / Images / Color Palette Extract API

Color Palette Extract API

Extracts an image's dominant colours as a small palette (hex, RGB and coverage fraction).

Endpoint: POST /v1/color-palette-extract
Price: $0.003 per call
Family: Images
Docs: /docs/color-palette-extract

01When to use it

Extracting a palette safely needs a real decoder and a hardened fetch: an agent that pulls the URL itself walks past every SSRF control, and a byte-reproducible quantiser is not something an agent writes inline.

When not to use it

The input is over 25 MB (26,214,400 bytes): color-palette-extract answers too_large (413).
The destination needs more than 60 s to answer: the call ends with upstream_timeout (424).
The destination is on a private or local network: the network guard refuses it with blocked_target (403).

02Parameters

Field	Type	Required	Description
url	string	yes	Absolute http(s) URL of the image, up to 2048 characters; redirects are followed and the format is detected from the bytes, not the content-type.
colors	integer	no	Maximum number of palette colours to return, 1 to 16, most common first; fewer come back when the image has fewer distinct colour buckets. Default: 5.

03Limits

Limit	Value
Size cap	25 MB (26,214,400 bytes)
Timeout	60 s

04Example

The published example of color-palette-extract, verbatim: the request body and the response it returns.

Request

POST /v1/color-palette-extract
content-type: application/json
payment-signature: <base64 x402 payload>

{
  "url": "https://grist.tools/samples/images/palette-bands.png",
  "colors": 5
}

Response

200 OK
payment-response: <base64 settlement receipt>

{
  "source_url": "https://grist.tools/samples/images/palette-bands.png",
  "source_format": "png",
  "sample_size": 64,
  "count": 5,
  "dominant": "#3b4a5a",
  "colors": [
    {
      "hex": "#3b4a5a",
      "rgb": [
        59,
        74,
        90
      ],
      "fraction": 0.375
    },
    {
      "hex": "#d8c9a3",
      "rgb": [
        216,
        201,
        163
      ],
      "fraction": 0.25
    },
    {
      "hex": "#2f8f83",
      "rgb": [
        47,
        143,
        131
      ],
      "fraction": 0.1875
    },
    {
      "hex": "#e0735a",
      "rgb": [
        224,
        115,
        90
      ],
      "fraction": 0.125
    },
    {
      "hex": "#f4efe6",
      "rgb": [
        244,
        239,
        230
      ],
      "fraction": 0.0625
    }
  ]
}

Sample file: images/palette-bands.png. 64x64 PNG of five flat vertical colour bands, 24, 16, 12, 8 and 4 pixels wide, built from raw pixels with the pinned PNG encoder.

In the sample itself: its IHDR chunk declares 64 by 64 pixels, 8-bit truecolour RGB and no interlacing. The chunks run IHDR, pHYs, IDAT and IEND.

Response field	Type	In the example
source_url	string	"https://grist.tools/samples/images/palette-bands.png"
source_format	string	"png"
sample_size	number	64
count	number	5
dominant	string	"#3b4a5a"
colors	array	5 items, each with hex, rgb and fraction

05Call it from code

JavaScript

// color-palette-extract: $0.003 per call, paid in USD Coin on eip155:8453 via x402
// Install: npm install @x402/fetch@2 @x402/evm@2 viem@2
// Save as client.mjs (ES module, Node 18+), export EVM_PRIVATE_KEY with the paying wallet's key in your shell, then run: node client.mjs
// The wrapper reads the 402 (payment-required), signs and retries with payment-signature.
import { wrapFetchWithPayment, x402Client, decodePaymentResponseHeader } from '@x402/fetch'
import { ExactEvmScheme } from '@x402/evm/exact/client'
import { privateKeyToAccount } from 'viem/accounts'

const account = privateKeyToAccount(process.env.EVM_PRIVATE_KEY)
const client = new x402Client().register('eip155:8453', new ExactEvmScheme(account))
const fetchWithPayment = wrapFetchWithPayment(fetch, client)

const body = {
  "url": "https://grist.tools/samples/images/palette-bands.png",
  "colors": 5
}

const res = await fetchWithPayment('https://grist.tools/v1/color-palette-extract', {
  method: 'POST',
  headers: { 'content-type': 'application/json' },
  body: JSON.stringify(body),
})
console.log(res.status, await res.json())
const settle = res.headers.get('payment-response')
if (settle) console.log(decodePaymentResponseHeader(settle).transaction)

Python

# color-palette-extract: $0.003 per call, paid in USD Coin on eip155:8453 via x402
# Install: pip install "x402[requests,evm]>=2.24,<3"
# The session reads the 402 (payment-required), signs and retries with payment-signature.
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http import decode_payment_response_header
from x402.http.clients.requests import x402_requests
from x402.mechanisms.evm.exact import register_exact_evm_client
from x402.mechanisms.evm.signers import EthAccountSigner

account = Account.from_key(os.environ["EVM_PRIVATE_KEY"])
client = x402ClientSync()
register_exact_evm_client(client, EthAccountSigner(account), networks="eip155:8453")
session = x402_requests(client)

payload = {
    "url": "https://grist.tools/samples/images/palette-bands.png",
    "colors": 5
}

res = session.post("https://grist.tools/v1/color-palette-extract", json=payload)
print(res.status_code, res.json())
settle = res.headers.get("payment-response")
if settle:
    print(decode_payment_response_header(settle).transaction)

curl

# color-palette-extract: $0.003 per call, paid in USD Coin on eip155:8453 via x402
# 1. Unpaid call: HTTP 402, the requirements in the payment-required header (base64 JSON) and in the body.
curl -i -X POST 'https://grist.tools/v1/color-palette-extract' -H 'content-type: application/json' -d '{"url":"https://grist.tools/samples/images/palette-bands.png","colors":5}'

# 2. Same call with the signed payment (an EIP-3009 authorization, EIP-712 signed: it cannot be
#    typed by hand). x-payment is accepted as the v1 alternative. HTTP 200 carries payment-response.
curl -i -X POST 'https://grist.tools/v1/color-palette-extract' -H 'content-type: application/json' -H 'payment-signature: <base64 x402 payload>' -d '{"url":"https://grist.tools/samples/images/palette-bands.png","colors":5}'

06Errors

Code	HTTP	For this service
invalid_input	400	The body does not match the schema; its fields are url and colors.
blocked_target	403
unreachable_target	424
upstream_timeout	424
unsupported_content_type	415
too_large	413
unprocessable	422
internal	500

Input that is rejected before the tool runs (malformed JSON, schema mismatch, body over the size limit) is never charged.

When each code is raised, and what it means for payment: /docs/color-palette-extract.

07Questions

How much does a color-palette-extract call cost?: $0.003 per call, paid in USDC on Base via x402, with no account and no API key.
What does color-palette-extract return?: A JSON object with 6 top-level fields: source_url, source_format, sample_size, count, dominant and colors. The example on this page is a real call over images/palette-bands.png.
What happens when a color-palette-extract call fails?: The tool answers with a typed JSON error from the errors table. Payment is settled only after the tool has produced its result; a call that fails inside the tool is never settled. A 503 upstream_unavailable can follow a settled call; the x402 payments guide covers it, 429, 402 and an uncertain 500.