Paste your HTML into the thirds.ai editor or send it to the API, pick a size, and you get back a finished PNG, JPEG, or WebP. A free converter gives you one picture and forgets your code. Running Puppeteer yourself means fonts that go missing and a browser that breaks when it updates. Here you save the HTML once as a design, and every link preview, thumbnail, or sale post after that comes from it, with new text and in every size, from your app or from ChatGPT or Claude. Start from a gallery template with your brand kit, and each image comes out in your logo and colours too.
Free to start, and you don't need a card.
HTML to image
Here's how to turn HTML into PNG, JPEG, or WebP images with an API... in every size you need!
Start with an HTML design. This gig poster comes from our template gallery. Every field in curly braces, like the artist, the date, or a colour, gets filled in from your data.
Save it once with a POST to /v1/templates, and you get back a template ID.
Now send your data to /v1/image. Name the template, fill in the fields... then pick a format and a size. Here, a PNG, 1080 × 1350.
Press Enter... and there's your poster!
Got another show? Just change the data. A new name, new colours, and JPEG in place of PNG. Same template, a whole new poster.
Need every size? Send one request to /v1/image-packs. List the sizes you want, like a square post and a story... and ask for WebP.
The design rearranges itself to fit each size, and every file comes back in one ZIP. One credit for each image.
Start free with 50 credits a month, at thirds.ai.
Your own HTML
Paste your HTML into the thirds.ai editor, pick a size, and download it as a PNG, JPEG, or WebP in three steps. Your code stays saved as a design, so smart resize gives you every extra size, and your app or your AI assistant can make the next picture without you.
Try it now
Put your own details and brand on a designer-made post, and download the PNG free. You'll see what your HTML can look like as a thirds.ai design before you paste a line of it.
Pick a quick example, or put your own headline and price in the boxes.
Click Your brand and choose yours. The design changes to your colours and logo.
Click Download free to sign in and save the PNG.
Change a line and make a real image.
When you want more
Most images you need come back again and again, like a link preview for each new page or a thumbnail for each episode. With thirds.ai you save that HTML once as a design, and every picture after it comes out in your brand.
Paste the HTML you already have and mark the parts that change. From then on your app, your AI assistant, or a spreadsheet fills them in, and there's no browser for you to run or keep up to date.
Save your HTML as a design
Get a story and a square post from the same design, each laid out to fit its size.
Learn more about Every size from one designGet a new image by asking ChatGPT or Claude for it in plain words.
Learn more about Pictures from your AI assistantTurn a spreadsheet of products or posts into a full set of images at once.
Learn more about A batch from a spreadsheet or your appFrom your own code
When your app needs a picture for each event, product, or post, it sends one request to POST /v1/image with the ID of your saved design and the new details, and gets back a finished image ready to use. Nobody opens a design tool, and there's no browser to run on your own servers.
curl --fail-with-body --silent --show-error \
https://thirds.ai/v1/image \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: YOUR_UNIQUE_IMAGE_REQUEST" \
--data '{
"template_id": "tpl_YOUR_EVENT_PROMO_ID",
"version": 1,
"data": {
"month": "October",
"day": "14",
"time": "3:00 PM London",
"host": "Fieldnote sessions",
"title": "Plan a client launch in one afternoon",
"description": "A practical workshop for small teams that want one clear story and a reusable launch kit.",
"action": "Save your place"
},
"image": {"format": "png", "width": 1200, "height": 630},
"wait": false
}'
Smart resize
A sale post needs a story and a link preview too, and resizing by hand means fixing the layout each time. Click Smart resize on a saved image design, add the sizes you need, and the layout fits each one on its own. Then click Export pack, and every size downloads together in one ZIP.
From your AI assistant
Connect thirds.ai to ChatGPT, Claude, Gemini, Grok, or any other AI you use, and ask for a thumbnail for the new episode in plain words. The assistant finds the episode title and brings the finished picture back in the chat. It comes from your saved design, in your brand, so you can post it straight away.
Templates
Any picture a browser can draw: a link preview for each page on your site, a thumbnail for each video, a banner for every newsletter, or a tall card of your best numbers. Start from a designer-made template in the thirds.ai gallery, and it comes out in your brand kit. Each template shows its HTML, so you can read how it's built before you copy it.
For developers and agents
Your code sends raw HTML with a width and height, and downloads the finished image when it's ready. Or it sends a saved design's ID and gets every size in one ZIP from one request. Your AI agent makes images through the MCP server from the same designs your team edits in the browser.
curl --fail-with-body --silent --show-error \
https://thirds.ai/v1/image \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: YOUR_UNIQUE_IMAGE_REQUEST" \
--data '{
"html": "<h1>September report</h1><p>24 orders completed</p>",
"image": {"format": "png", "width": 1200, "height": 630}
}'curl --fail-with-body --silent --show-error \
https://thirds.ai/v1/image-packs \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: autumn-sale-pack-01" \
--data '{
"template_id": "tpl_YOUR_TEMPLATE",
"version": 3,
"data": {"headline": "Autumn sale"},
"format": "png",
"sizes": ["square-post", "story", "1200x628"]
}'{
"servers": {
"thirds": {
"type": "http",
"url": "https://thirds.ai/mcp",
"headers": {
"Authorization": "Bearer YOUR_API_KEY"
}
}
}
}You send the HTML itself. thirds.ai doesn't open a website address, so your design never has to be online, and you can make a picture from HTML that lives only in your app.
Pick PNG for sharp text and flat colours, JPEG for photos, and WebP for a smaller file. PNG and WebP can keep a transparent background for a logo or a badge. A JPEG always has a solid background. Reduce image file size.
Yes. A real Chromium browser lays out your page, so grid, flexbox, and web fonts all work. Pictures and fonts can come from public web addresses or from files you upload to your account. Compare with HTML/CSS to Image.
Use 1200 × 630 for a link preview, 1080 × 1080 for a square post, and 1080 × 1920 for a story. The editor has each one as a preset, and one design can hold all three. Try the Open Graph image generator. Make social images from one design.
Yes. Save your HTML as one design, then open Batches in the studio and upload a CSV with one row for each image. The finished images download together in one ZIP file. Make a batch from a CSV.
Every image lands on the Renders page in your account, whether the website, your code, or your AI assistant made it. It stays for up to a year on a paid plan and 30 days on the Free plan, and you can download it again or open the design that made it. Retry and download.
Yes. The same HTML makes a PDF with a paper size and margins instead of a width and height, from the editor or from POST /v1/pdf. Convert HTML to PDF.
Yes. Make the sample post with your own details, or paste your HTML into the editor and preview it. A verified free account gets 50 credits each month, so you can test your own HTML before you pay anything. An image that fails costs nothing.
HTML to image
Paste your HTML or pick a template, and download a finished PNG free. Save it as a design, and your app or your AI assistant makes every picture after it.