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What a screenshot webhook receiver does
For an asynchronous screenshot request, a provider can send the completed result to a URL you specify. Your server must expose that endpoint to the provider, accept its HTTP POST, authenticate the request using the provider’s documented signing scheme, validate the event, and acknowledge it with the status code the provider expects.
A callback URL is not authentication by itself. Anyone who discovers a public URL might be able to send it a request. Verify the signature before trusting the body, and keep signing secrets on the server.
Check the provider’s callback contract first
There is no universal screenshot webhook header or signing convention. Confirm that asynchronous callbacks are available for your account and deployment, then follow that provider’s current documentation.
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| Provider documentation | Callback and signature details | Important qualification |
|---|---|---|
| Screenshot API (screenshotapis.org) | The guide describes a webhook_url, an immediate 202 Accepted, a later POST, and an X-Webhook-Signature HMAC-SHA256 hex digest of the JSON body signed with the API key. |
The guide says async callbacks currently return 503 without charging a credit on that deployment and recommends synchronous rendering. Do not assume its illustrated callback flow is active there. |
| ScreenshotMAX | Signing is optional via webhook_signed. When enabled, X-Screenshotmax-WebHook-Signature contains an HMAC-SHA256 signature using secret_key and the payload. Verify the exact raw JSON body. |
The callback URL must be publicly reachable over HTTP or HTTPS, accept POST, and return a 2xx response to acknowledge the event. |
| ScreenshotOne | Async requests can use webhook_url. Its X-ScreenshotOne-Signature is verified with HMAC-SHA256 over the raw text body and a secret key. |
The signing secret is distinct from the API key. The vendor’s Node example reads the raw request text before verifying it. |
These documented differences mean you must not copy a header or secret assumption from one provider into another integration. The sources do not establish one retry policy, delivery ordering, or exactly-once guarantee shared by all providers.
Implement a raw-body receiver with Express
The following is a provider-adaptable pattern using Express and Node’s built-in crypto module. It shows the ScreenshotOne header and secret convention as a concrete example; change the header, secret, digest encoding, and any signature prefix handling to match the provider you actually use. ScreenshotOne’s guide documents HMAC-SHA256 and its separate secret key.
Install Express with npm install express. Set SCREENSHOTONE_WEBHOOK_SECRET in the server environment; do not put a real secret in source control or a browser-facing application.
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import express from 'express';
import { createHmac, timingSafeEqual } from 'node:crypto';
const app = express();
const secret = process.env.SCREENSHOTONE_WEBHOOK_SECRET;
if (!secret) throw new Error('Missing SCREENSHOTONE_WEBHOOK_SECRET');
function safeHexEqual(received, expected) {
if (typeof received !== 'string' || !/^[0-9a-f]+$/i.test(received)) return false;
const receivedBytes = Buffer.from(received, 'hex');
const expectedBytes = Buffer.from(expected, 'hex');
return receivedBytes.length === expectedBytes.length &&
timingSafeEqual(receivedBytes, expectedBytes);
}
app.post('/webhooks/screenshot', express.raw({ type: 'application/json' }), async (req, res) => {
if (!Buffer.isBuffer(req.body)) return res.status(415).send('Expected JSON body');
const signature = req.get('X-ScreenshotOne-Signature');
const expected = createHmac('sha256', secret).update(req.body).digest('hex');
if (!safeHexEqual(signature, expected)) return res.status(401).send('Invalid signature');
let event;
try {
event = JSON.parse(req.body.toString('utf8'));
} catch {
return res.status(400).send('Invalid JSON');
}
// Validate the event shape and expected job/status before acting on it.
if (!event || typeof event !== 'object') return res.status(400).send('Invalid event');
try {
await handleScreenshotEvent(event);
return res.sendStatus(200);
} catch (error) {
console.error('Screenshot webhook processing failed', error);
return res.sendStatus(500);
}
});
async function handleScreenshotEvent(event) {
// Persist or enqueue the verified event here.
}
app.listen(process.env.PORT || 3000);This example assumes the documented signature is an unprefixed hexadecimal HMAC-SHA256 value. If your provider adds a prefix, uses another encoding, or signs different bytes, adapt verification to its specification. Header names are case-insensitive in HTTP; framework accessors such as req.get() handle normal header casing.
Keep the raw route ahead of JSON parsing
express.raw() gives this route the original body as a Buffer. Do not run express.json() first and then serialize the parsed object to verify it. JSON whitespace, property order, and escaping can change during parsing and reserialization, so the resulting bytes may not match what the provider signed.
If the application uses global middleware, register this route before express.json(), or selectively exclude this route from the JSON parser. Configure the parser media type to match the provider’s content type; if the vendor sends a different type, adjust the route deliberately rather than silently parsing or trusting it.
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Use the right acknowledgment and processing model
Return the status required by the provider’s contract after signature verification and the work your endpoint promises to complete. ScreenshotMAX says its endpoint should return a 2xx acknowledgment. The screenshotapis.org guide describes an initial 202 Accepted for the screenshot request, but also says callbacks are currently unavailable on its deployment. Do not confuse the status returned when you submit a render request with the acknowledgment returned by your webhook receiver.
For short processing, you can validate and handle the event before returning success. For slow or failure-prone work, persist the verified event or enqueue it, then respond once that durable handoff succeeds. Acknowledge before durable acceptance only if losing that work is acceptable. If processing fails before acknowledgment, return an error only as permitted by the provider’s current delivery contract; do not assume it will retry.
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Make duplicate handling safe
Design the handler to tolerate a repeated event where practical: store a provider event or job identifier with a uniqueness constraint, and make downstream updates idempotent. This is prudent receiver design, not a claim that any named provider guarantees duplicate delivery. Check the provider documentation for retry behavior, ordering, timeout limits, and duplicate semantics before depending on them.
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Provider-specific implementation changes
ScreenshotOne
Use X-ScreenshotOne-Signature and the ScreenshotOne secret key, not the API key. Its documentation’s Node.js example reads request.rawText() and verifies an HMAC-SHA256 signature. Never expose the signing key to a client or include it in logs.
ScreenshotMAX
Configure signed callbacks with webhook_signed and use the secret_key and X-Screenshotmax-WebHook-Signature convention described by its guide. Signing is optional there; for a receiver that relies on authentication, enable signed mode and verify the exact raw body. Its callback URL must be publicly accessible via HTTP or HTTPS, and it documents a 2xx acknowledgment.
Screenshot API at screenshotapis.org
Although its guide illustrates webhook_url and an X-Webhook-Signature signed with the API key, that same guide says callbacks currently return 503 on its deployment and recommends synchronous rendering. Check that availability note for your deployment before building around the illustrative flow.
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- Expose a stable route, such as
POST /webhooks/screenshot, at a public HTTPS URL. A localhost address is not reachable by a hosted screenshot service. - Store the provider’s callback signing secret in a server-side environment variable or secret manager. Keep it separate from client configuration and rotate it using the provider’s documented process if exposed.
- Ensure the route retains raw request bytes and that no middleware rewrites them before signature verification.
- Test the valid-signature path, invalid signature, malformed JSON, unexpected event shape, and downstream processing failure. Confirm the response status and that invalid requests produce no side effects.
- Submit an actual asynchronous render with your endpoint configured, if the provider supports it on your deployment. Confirm the provider can reach the URL and that the expected callback is received.
- Monitor request status, processing failures, and queue depth without logging secrets or unnecessarily recording sensitive screenshot contents.
Troubleshooting common failures
- Signature fails for an otherwise valid JSON body: Verify against the original raw bytes, not parsed-and-reserialized JSON. Check the exact secret, HMAC algorithm, header, encoding, and any required signature prefix.
- Request body is an object rather than a buffer: A JSON parser likely ran before the raw route parser. Reorder or scope middleware so the webhook route receives raw data.
- Webhook never arrives: Confirm the configured URL is publicly reachable, uses a supported HTTP/HTTPS endpoint, and accepts POST. Check whether asynchronous callbacks are available for this provider and deployment; screenshotapis.org’s guide currently documents unavailability on its deployment.
- Provider reports an unacknowledged event: Check the receiver’s returned status, route timeout, and whether an exception occurs before the acknowledgment. ScreenshotMAX specifically documents a 2xx response requirement; check the selected provider’s current contract for the rest.
- Valid requests get a content-type rejection: Compare the received content type with the type accepted by the raw parser and adjust the route configuration to match the provider’s documented request.
- Events appear more than once or out of sequence: Do not assume exactly-once delivery or ordering. Use stable event/job identifiers and idempotent state transitions, and consult the provider for its actual delivery guarantees.
- Callback feature is absent from the account or deployment: Check current product documentation and settings. Where async delivery is unavailable, use the provider’s synchronous rendering path rather than relying on an inactive webhook example.
Or skip the browser setup
If your goal is to obtain screenshots rather than operate a browser capture pipeline, ScreenshotNeo offers a one-request screenshot API and MCP server. It does not replace the webhook receiver pattern above for another provider; it is an alternative capture service with different workflow options.
For a screenshot call, use the API key and target URL. See the ScreenshotNeo API documentation for available parameters and response details.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpScreenshotNeo removes cookie and consent banners, newsletter popups, and chat widgets before capture; bot checks, blank pages, and failed loads are not billed. AI agents can use its MCP server, and the free plan includes 1,000 screenshots per month without a card; paid plans start at $5 for 3,000. Sign up for 1,000 free screenshots a month with no card.
Frequently Asked Questions
Can I verify a webhook after parsing its JSON?
No. Verify the provider signature against the original raw bytes first; parsing and reserializing can change the signed representation.
Do screenshot webhook providers all retry failed deliveries?
The cited provider guides do not establish a shared retry policy. Check the current delivery documentation for your selected provider.
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