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Agent Preflight APIs – Email HTML Validator
x402
Agent Preflight APIs – Email HTML Validator is a paid API for AI agents from email-preflight-api.vercel.app, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).
Deterministically validates email HTML for deliverability issues, clipping risk, and compatibility problems before an agent sends a campaign or transactional message.
Price / call$0.01
Success—
StatusUnknown
How this service works
Pre-action x402 payment checks and deterministic email HTML validation for AI agents.
Output
Returns a JSON object with an 'ok' boolean, a list of detected issues, detailed metrics (link count, image count, inline style bytes, script block bytes, comment bytes, base64 image bytes, images without alt text), a clipping risk assessment (risk level, HTML byte size, headroom, threshold, percent of threshold), service name, version, and a limitations disclaimer. An empty issues array with ok:true means no problems were detected.
Example use cases
Pre-send campaign clipping check
“I'm about to send this newsletter HTML to 10,000 subscribers — can you run it through the email preflight validator to see if it's at risk of being clipped by Gmail and flag any other issues? Here's the HTML.”
Transactional email QA in agent workflow
“My agent just generated an order confirmation email. Before it sends, validate the HTML for missing alt text on images, embedded scripts, oversized style blocks, and clipping risk.”
Bulk template audit before deployment
“I have a new email template I want to deploy — check the HTML for compatibility issues like inline styles, base64 images, script blocks, and tell me how close it is to the 102,400 byte clipping threshold.”
Technical details
Endpoint
POSThttps://email-preflight-api.vercel.app/api/preflightWhen to prefer
Use this endpoint when an AI agent is about to send an email and needs a fast, deterministic, pre-send sanity check on raw HTML — specifically to catch Gmail clipping risk (>102KB), missing alt text, embedded scripts, bloated style blocks, or base64 images before they reach an inbox. Prefer this over manual review or full inbox-placement testing services when you need a cheap ($0.01), programmatic, no-side-effect check that runs inline in an agentic workflow.
Side effects
- Malformed or non-HTML input may return validation errors or unexpected issue lists
- Very large HTML payloads may be rejected or return clipping risk as high
- Payment failure via x402 protocol results in a 402 response before analysis begins
- Dynamic merge tags and platform-injected footer content are not accounted for in byte size calculations
- Results reflect static source analysis only — actual inbox rendering may differ
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| html | string | One complete email HTML source document, up to 512,000 UTF-8 bytes. Do not include subscriber data. |
Output
Schema · Response
{
"type": "json",
"example": {
"ok": true,
"issues": [],
"metrics": {
"links": 1,
"images": 0,
"commentBytes": 0,
"styleBlockBytes": 0,
"imagesWithoutAlt": 0,
"inlineStyleBytes": 0,
"scriptBlockBytes": 0,
"embeddedBase64ImageBytes": 0
},
"service": "email-preflight",
"version": "2026-07-31",
"clipping": {
"risk": "low",
"htmlBytes": 88,
"headroomBytes": 102312,
"thresholdBytes": 102400,
"percentOfThreshold": 0.1
},
"limitations": [
"This is deterministic source analysis, not inbox-placement or rendering testing.",
"Merge tags and platform-added footer content can change final message size.",
"A missing issue does not guarantee compatibility with every email client."
]
}
}Tags
x402
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