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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →To generate an Open Graph (OG) image from HTML with HTML/CSS to Image, either send HTML and optional CSS to its image API, or configure an OG Image Config to generate cards from pages on your site. Then put the resulting public, absolute image URL in the page’s server-rendered <head>. A rendered image alone does not create a social preview: crawlers also need to find the right metadata, and both HTML/CSS to Image and the social platform may cache results.
Choose direct rendering or automatic page-based cards
Use the direct API when your application or build process creates the markup and needs an image for a particular request. Use an OG Image Config when you want image URLs mapped to pages across a public site, such as a blog or store. The first gives your application more control over the input; the second is designed to associate a site origin and page paths with generated cards.
| Workflow | Input and output | Best fit |
|---|---|---|
| Direct image API | POST HTML or a public page URL to https://hcti.io/v1/image; receive an image URL and ID. |
On-demand renders or application-controlled content. |
| OG Image Config | Map a public site origin to path-based HCTI image URLs. | Automated cards for multiple pages on a site. |
Generate an image with the direct API
Choose the input
Send either an html value or a fully qualified public url, not both. Use html to render custom markup, with optional CSS in css. Use url to capture an existing public webpage; when supplied, it takes precedence over HTML input. The API documentation lists PNG, JPG, WebP, and PDF output options.
Authenticate and send a request
The endpoint is POST https://hcti.io/v1/image, authenticated with HTTP Basic: your API ID is the username and your API key is the password. Keep both credentials in trusted server-side code. The examples below use HTML input.
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curl -X POST https://hcti.io/v1/image
-u "YOUR_API_ID:YOUR_API_KEY"
-H "Content-Type: application/json"
-d '{"html":"<div class="card"><h1>Hello world</h1></div>","css":".card { width: 1200px; height: 630px; display: grid; place-items: center; background: #f4f6f8; font-family: sans-serif; } h1 { color: #18212f; }"}'For a public page, send the URL instead:
curl -X POST https://hcti.io/v1/image
-u "YOUR_API_ID:YOUR_API_KEY"
-H "Content-Type: application/json"
-d '{"url":"https://example.com/article"}'Use the returned image URL as the value of the page’s image metadata. Check the response for the image URL and ID before adding it to your page. See the HTML/CSS to Image API documentation for the current request and response details.
Python example
import requests
response = requests.post(
"https://hcti.io/v1/image",
auth=("YOUR_API_ID", "YOUR_API_KEY"),
json={
"html": '<div class="card"><h1>Hello world</h1></div>',
"css": ".card { width: 1200px; height: 630px; display: grid; place-items: center; background: #f4f6f8; font-family: sans-serif; } h1 { color: #18212f; }",
},
timeout=60,
)
response.raise_for_status()
result = response.json()
print(result)Node.js example
This example uses Node.js’s built-in fetch and Basic authentication. Keep the credentials in environment variables rather than in browser code.
const apiId = process.env.HCTI_API_ID;
const apiKey = process.env.HCTI_API_KEY;
if (!apiId || !apiKey) throw new Error('Set HCTI_API_ID and HCTI_API_KEY');
const auth = Buffer.from(`${apiId}:${apiKey}`).toString('base64');
const res = await fetch('https://hcti.io/v1/image', {
method: 'POST',
headers: {
Authorization: `Basic ${auth}`,
'Content-Type': 'application/json',
},
body: JSON.stringify({
html: '<div class="card"><h1>Hello world</h1></div>',
css: '.card { width: 1200px; height: 630px; display: grid; place-items: center; background: #f4f6f8; font-family: sans-serif; } h1 { color: #18212f; }',
}),
});
if (!res.ok) throw new Error(`HCTI request failed: ${res.status} ${await res.text()}`);
const result = await res.json();
console.log(result);Set up automatic cards with an OG Image Config
Map your public pages
An OG Image Config associates a public site origin you own or administer with an HCTI image URL. HCTI uses the path in that image URL to request the corresponding page, read its metadata, and screenshot the page or render a configured template. Page metadata can supply values such as a title, description, Open Graph fields, or explicit template variables.
- Configure the site’s public HTTPS origin in the OG Image Config.
- Use the configured domain ID in the HCTI image URL and give each page a distinct path, for example
https://hcti.io/v1/og/DOMAIN_ID/articles/my-post. - Put that absolute URL in the page’s server-rendered metadata, including
og:imageandtwitter:image. - Publish and verify the resulting page source and image URL.
Replace DOMAIN_ID with the ID supplied by your configuration. The path identifies the page; query strings are ignored for this mapping. Use unique paths for distinct pages.
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<head>
<meta property="og:image" content="https://hcti.io/v1/og/DOMAIN_ID/articles/my-post">
<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:image" content="https://hcti.io/v1/og/DOMAIN_ID/articles/my-post">
</head>These tags need to be in the HTML returned by your server. Do not rely on JavaScript that inserts them only after the page loads: social crawlers may not read that change. If a theme or SEO plugin already emits image metadata, update its value or use its supported filter instead of adding competing tags. Follow the OG Image Config guide for configuration details.
Choose how images adapt to platforms
The config guide describes three approaches: use one image everywhere, render once and adapt to platform bounds, or create separate renders for recognized viewports. A single image is simplest. Adapting one render avoids stretching but may leave unused space. Separate renders can fit responsive designs more closely but use multiple renders.
HTML/CSS to Image recommends 1200 × 630 pixels as a broad fallback. Its current social-card guide lists these platform-specific recommendations; they are the service’s guidance, not a guarantee of an immutable platform standard.
| Platform | Recommended dimensions |
|---|---|
| 1200 × 600 | |
| 1200 × 630 | |
| 1200 × 627 | |
| Slack | 1200 × 630 |
For HTML snippet rendering, output is automatically cropped to the outermost HTML element and rendered at 2× by default. That means a CSS width of 400 pixels can produce an 800-pixel-wide output. If the returned dimensions seem larger than expected, distinguish the CSS layout dimensions from the final pixel dimensions. See the dimensions guidance.
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Publish metadata crawlers can read
For a useful preview, the page itself must expose the intended absolute image URL in its server-rendered <head>. The official setup example uses og:image, twitter:card set to summary_large_image, and twitter:image. Confirm there is one authoritative image value rather than conflicting tags from your application, theme, or SEO plugin.
- Publish the page, then use View Source to confirm its final
<head>contains the intendedog:imageandtwitter:image. - Open the HCTI image URL directly and confirm that it returns an image.
- Use HTML/CSS to Image’s Social Card Previewer to inspect metadata and platform-specific shapes.
- If the image is current at HCTI but stale in a social app, inspect that platform’s preview cache separately.
Protect credentials and public image URLs
Keep API credentials server-side
HTML/CSS to Image’s API documentation says, “Treat your API Key like a password.” Do not expose the API ID or key in client-side JavaScript or public source. The direct API flow uses HTTP Basic authentication, so make the request from trusted server-side code.
Use signed URLs only for suitable public inputs
A signed URL can be embedded publicly, but its HMAC SHA256 signature must be created on your server with the secret API key. Anyone holding that URL can request the image it authorizes, so only sign inputs and permissions appropriate for public access. An OG Image Config may be more suitable when public pages and their metadata fit the origin-and-path mapping; use direct API rendering or a signed URL when the application needs arbitrary values at request time. See the signed URL guide.
Why a social preview can still show an old image
There are three separate caches to consider: source-page metadata, the rendered HCTI image, and the social platform’s own preview. A fresh image at one layer does not force the next layer to refresh immediately.
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Check the HCTI refresh cycle
The current OG Image documentation specifies a 24-hour default refresh interval for a config, with plan-dependent minimums. Source-page Cache-Control freshness headers or Expires can extend the next metadata check. On the first request after metadata has gone stale, HCTI may return the existing image while a background refresh runs; a subsequent request can reflect updated inputs. Consult the caching guide and dashboard guidance for the applicable refresh controls.
Change content at the same path
Adding a random query parameter to an OG Config image URL does not bust HCTI’s cache. If the pixels changed but the extracted metadata did not, the guide documents hcti:content_version as a monotonically increasing integer. Increment it when you need a new image identity for changed content at the same path.
Refresh the destination platform
Once the image URL serves the current image, use the destination platform’s rescrape or inspection tool if one is available. The platform may retain its own cached preview independently of HCTI.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Common problems and fixes
| Symptom | Likely cause | What to check or do |
|---|---|---|
| The API request is unauthorized. | The API ID or key is wrong, missing, or not sent as HTTP Basic credentials. | Verify the credentials server-side and confirm the API ID is the username and API key the password. |
| The request renders unexpected input. | Both html and url were sent; the URL takes precedence. |
Send exactly one input: custom HTML, or a fully qualified public URL. |
| The image URL works, but no preview appears. | The page’s tags may be absent from server-rendered HTML, malformed, or overridden by another SEO source. | Inspect View Source, confirm one absolute og:image and matching twitter:image, and open the image URL directly. |
| The image looks cropped or has unexpected dimensions. | HTML snippet output is cropped to its outermost element and rendered at 2× by default. | Check the outer element’s bounds and compare CSS dimensions with returned pixel dimensions. |
| The social app shows an earlier card. | HCTI or the destination platform may still have cached metadata or pixels. | Check source cache headers and the HCTI refresh interval, then use the platform’s rescrape tool if available. Do not rely on a query string to invalidate an OG Config image. |
Performance, reliability, and cost considerations
- Allow for multiple cache layers. Automatic configs can reuse rendered images while metadata refreshes; source cache headers can lengthen that interval, and social apps have independent caches.
- Plan for the correct render shape. A single broadly sized card is simpler; adapting or separate platform renders can better fit different bounds, with the latter using multiple renders.
- Protect availability of the source page. A URL-based render or path-mapped config depends on the relevant public page being accessible to the service when it requests it.
- Keep cost claims in context. The cited documentation describes the workflows and caching behavior but does not establish a price for this article’s examples. Check HTML/CSS to Image’s current pricing and plan terms before estimating recurring usage.
Or skip the browser setup
If you only need a screenshot of an existing public page, ScreenshotNeo provides a one-call screenshot API. For the HTML-to-OG workflow above, HTML/CSS to Image accepts HTML templates directly; ScreenshotNeo’s API takes a URL. Use it when capturing a rendered page is the better fit.
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Frequently asked questions
Can I render HTML without hosting it on a public site?
Yes. The direct API accepts HTML as input, so you can submit custom markup and optional CSS without first publishing that markup as a webpage.
Can I use one generated image for every social platform?
Yes. The OG Image Config guide supports using one image everywhere; its broad fallback recommendation is 1200 × 630 pixels. Platform-specific shapes are available if you need them.
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