Recipes

Migrating from QuickChart

Move your QuickChart URLs to ChartPNG and fix the configs that need it.

1. Change the domain

The c parameter and the JSON config keep their names. For many URLs this is the whole change.

Before

https://quickchart.io/chart?w=600&h=360&c=%7B%22type%22%3A%22bar%22%2C%22data%22%3A%7B%22labels%22%3A%5B%22Mon%22%2C%22Tue%22%2C%22Wed%22%5D%2C%22datasets%22%3A%5B%7B%22label%22%3A%22Signups%22%2C%22data%22%3A%5B12%2C19%2C7%5D%7D%5D%7D%2C%22options%22%3A%7B%22title%22%3A%7B%22display%22%3Atrue%2C%22text%22%3A%22Signups%20per%20day%22%7D%2C%22legend%22%3A%7B%22display%22%3Afalse%7D%2C%22scales%22%3A%7B%22yAxes%22%3A%5B%7B%22ticks%22%3A%7B%22beginAtZero%22%3Atrue%7D%2C%22scaleLabel%22%3A%7B%22display%22%3Atrue%2C%22labelString%22%3A%22Signups%22%7D%7D%5D%2C%22xAxes%22%3A%5B%7B%22scaleLabel%22%3A%7B%22display%22%3Atrue%2C%22labelString%22%3A%22Day%22%7D%7D%5D%7D%7D%7D

After

https://chartpng.dev/chart?w=600&h=360&c=%7B%22type%22%3A%22bar%22%2C%22data%22%3A%7B%22labels%22%3A%5B%22Mon%22%2C%22Tue%22%2C%22Wed%22%5D%2C%22datasets%22%3A%5B%7B%22label%22%3A%22Signups%22%2C%22data%22%3A%5B12%2C19%2C7%5D%7D%5D%7D%2C%22options%22%3A%7B%22title%22%3A%7B%22display%22%3Atrue%2C%22text%22%3A%22Signups%20per%20day%22%7D%2C%22legend%22%3A%7B%22display%22%3Afalse%7D%2C%22scales%22%3A%7B%22yAxes%22%3A%5B%7B%22ticks%22%3A%7B%22beginAtZero%22%3Atrue%7D%2C%22scaleLabel%22%3A%7B%22display%22%3Atrue%2C%22labelString%22%3A%22Signups%22%7D%7D%5D%2C%22xAxes%22%3A%5B%7B%22scaleLabel%22%3A%7B%22display%22%3Atrue%2C%22labelString%22%3A%22Day%22%7D%7D%5D%7D%7D%7D

Not every config survives the move unchanged. The next step is the one that matters.

2. Check the Chart.js version

ChartPNG renders Chart.js v4 today, and nothing else. QuickChart's default is older. Its FAQ says the default is v2.9.4, and that you set version=4 to use a v4 config.

• Your URLs have version=4: the config is already in the right format. Remove the version parameter, because ChartPNG refuses it.
• Your URLs have no version, or a lower one: you have a v2 config. ChartPNG does not convert it. You rewrite the options in the v4 format.

A v2 config that is valid JSON and uses one of the eight supported chart types does not fail: the bars still draw, and the options v4 does not know are ignored. A config with type: "horizontalBar", a QuickChart-only chart type or JavaScript syntax is refused with a 400. Here is the same config on ChartPNG, before and after the rewrite.

Before: Chart.js v2 (QuickChart's default)

{
  "type": "bar",
  "data": {
    "labels": [
      "Mon",
      "Tue",
      "Wed"
    ],
    "datasets": [
      {
        "label": "Signups",
        "data": [
          12,
          19,
          7
        ]
      }
    ]
  },
  "options": {
    "title": {
      "display": true,
      "text": "Signups per day"
    },
    "legend": {
      "display": false
    },
    "scales": {
      "yAxes": [
        {
          "ticks": {
            "beginAtZero": true
          },
          "scaleLabel": {
            "display": true,
            "labelString": "Signups"
          }
        }
      ],
      "xAxes": [
        {
          "scaleLabel": {
            "display": true,
            "labelString": "Day"
          }
        }
      ]
    }
  }
}

After: Chart.js v4 (what ChartPNG renders)

{
  "type": "bar",
  "data": {
    "labels": [
      "Mon",
      "Tue",
      "Wed"
    ],
    "datasets": [
      {
        "label": "Signups",
        "data": [
          12,
          19,
          7
        ]
      }
    ]
  },
  "options": {
    "plugins": {
      "title": {
        "display": true,
        "text": "Signups per day"
      },
      "legend": {
        "display": false
      }
    },
    "scales": {
      "y": {
        "beginAtZero": true,
        "title": {
          "display": true,
          "text": "Signups"
        }
      },
      "x": {
        "title": {
          "display": true,
          "text": "Day"
        }
      }
    }
  }
}

The URL that draws the v4 chart

https://chartpng.dev/chart?w=600&h=360&c=%7B%22type%22%3A%22bar%22%2C%22data%22%3A%7B%22labels%22%3A%5B%22Mon%22%2C%22Tue%22%2C%22Wed%22%5D%2C%22datasets%22%3A%5B%7B%22label%22%3A%22Signups%22%2C%22data%22%3A%5B12%2C19%2C7%5D%7D%5D%7D%2C%22options%22%3A%7B%22plugins%22%3A%7B%22title%22%3A%7B%22display%22%3Atrue%2C%22text%22%3A%22Signups%20per%20day%22%7D%2C%22legend%22%3A%7B%22display%22%3Afalse%7D%7D%2C%22scales%22%3A%7B%22y%22%3A%7B%22beginAtZero%22%3Atrue%2C%22title%22%3A%7B%22display%22%3Atrue%2C%22text%22%3A%22Signups%22%7D%7D%2C%22x%22%3A%7B%22title%22%3A%7B%22display%22%3Atrue%2C%22text%22%3A%22Day%22%7D%7D%7D%7D%7D

The changes you will meet most

The Chart.js v3 migration guide lists the rest.

3. Check the parameters

ChartPNG accepts QuickChart's long names, so these pairs mean the same thing:

• chart or c
• width or w
• height or h
• backgroundColor or bkg
• devicePixelRatio or dpr

Any other parameter is refused with a 400 and a message such as unknown parameter: version. That includesversion, v, format, f and key. A parameter given twice is refused too, and so are two names for one field, such as c and chart. Every distinct URL is a new render, so junk parameters are not allowed to bust the cache.

The defaults differ

The same URL with no size gives a different image. Set the values you need.

4. Functions are never run

QuickChart describes its config as a JavaScript or JSON object. ChartPNG reads strict JSON and never runs code. Fix these before you switch:

• JavaScript-only syntax such as single quotes, keys without quotes and trailing commas. ChartPNG answers chart config must be valid JSON.
• Functions such as tick callbacks and label formatters. A function written as a string stays a string and is not run. In a test on 2 Nov 2026, a string in ticks.callback made the tick labels disappear. Remove them, and format the numbers in your data or labels instead.

What else is different

• Chart types: bar, line, pie, doughnut, radar, polarArea, scatter and bubble.
• Output: PNG only.
• Plugins: Chart.js core and no third-party plugins.
• Size: the config can be up to 16 KB.
• Free plan: a small chartpng.dev watermark and up to 4 megapixels per image (width times height times dpr squared).
• Look: a chart that sets no colors gets the ChartPNG theme. Anything your config sets wins.