AI invoice generator: build one with Claude and PDF4.dev in 10 minutes

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8" />
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: 'Inter', sans-serif;
      font-size: 14px;
      color: #111;
      padding: 48px;
    }
    .header { display: flex; justify-content: space-between; margin-bottom: 40px; }
    .company-name { font-size: 24px; font-weight: 700; }
    .invoice-meta { text-align: right; }
    .invoice-number { font-size: 20px; font-weight: 600; color: #2563eb; }
    table { width: 100%; border-collapse: collapse; margin-top: 32px; }
    th { background: #f1f5f9; text-align: left; padding: 10px 12px; font-size: 12px; text-transform: uppercase; letter-spacing: 0.05em; }
    td { padding: 10px 12px; border-bottom: 1px solid #e2e8f0; }
    .total-row td { font-weight: 700; font-size: 16px; border-bottom: none; padding-top: 16px; }
    .due-date { color: #dc2626; font-weight: 600; }
  </style>
</head>
<body>
  <div class="header">
    <div>
      <div class="company-name">{{from.name}}</div>
      <div>{{from.address}}</div>
      <div>{{from.email}}</div>
    </div>
    <div class="invoice-meta">
      <div class="invoice-number">Invoice {{invoiceNumber}}</div>
      <div>Issued: {{issuedAt}}</div>
      <div class="due-date">Due: {{dueDate}}</div>
    </div>
  </div>
 
  <div>
    <strong>Bill to:</strong>
    <div>{{to.name}}</div>
    <div>{{to.email}}</div>
  </div>
 
  <table>
    <thead>
      <tr>
        <th>Description</th>
        <th>Qty</th>
        <th>Unit price</th>
        <th>Total</th>
      </tr>
    </thead>
    <tbody>
      {{#each items}}
      <tr>
        <td>{{description}}</td>
        <td>{{quantity}}</td>
        <td>${{unitPrice}}</td>
        <td>${{total}}</td>
      </tr>
      {{/each}}
    </tbody>
    <tfoot>
      <tr class="total-row">
        <td colspan="3">Total due</td>
        <td>${{totalAmount}}</td>
      </tr>
    </tfoot>
  </table>
 
  {{#if notes}}
  <p style="margin-top: 32px; color: #64748b; font-size: 12px;">{{notes}}</p>
  {{/if}}
</body>
</html>

const INVOICE_SCHEMA = {
  type: "object",
  properties: {
    invoiceNumber: { type: "string", description: "Invoice number, e.g. INV-2026-001" },
    issuedAt: { type: "string", description: "Issue date in DD MMM YYYY format" },
    dueDate: { type: "string", description: "Due date in DD MMM YYYY format" },
    from: {
      type: "object",
      properties: {
        name: { type: "string" },
        address: { type: "string" },
        email: { type: "string" }
      },
      required: ["name", "email"]
    },
    to: {
      type: "object",
      properties: {
        name: { type: "string" },
        email: { type: "string" }
      },
      required: ["name", "email"]
    },
    items: {
      type: "array",
      items: {
        type: "object",
        properties: {
          description: { type: "string" },
          quantity: { type: "number" },
          unitPrice: { type: "number" },
          total: { type: "number" }
        },
        required: ["description", "quantity", "unitPrice", "total"]
      }
    },
    totalAmount: { type: "number" },
    notes: { type: "string" }
  },
  required: ["invoiceNumber", "issuedAt", "dueDate", "from", "to", "items", "totalAmount"]
};

import express from "express";
import { extractInvoiceData } from "./claude";
import { renderInvoicePDF } from "./pdf4dev";
 
const app = express();
app.use(express.json());
 
app.post("/api/generate-invoice", async (req, res) => {
  const { prompt } = req.body;
 
  if (!prompt || typeof prompt !== "string") {
    return res.status(400).json({ error: "prompt is required" });
  }
 
  try {
    // 1. Extract structured data with Claude (~500ms)
    const invoiceData = await extractInvoiceData(prompt);
 
    // 2. Render PDF with PDF4.dev (~300ms)
    const pdfBuffer = await renderInvoicePDF(invoiceData);
 
    // 3. Return as download
    res.setHeader("Content-Type", "application/pdf");
    res.setHeader(
      "Content-Disposition",
      `attachment; filename="invoice-${invoiceData.invoiceNumber}.pdf"`
    );
    res.send(pdfBuffer);
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: "Invoice generation failed" });
  }
});
 
app.listen(3000, () => console.log("Server running on port 3000"));

curl -X POST http://localhost:3000/api/generate-invoice \
  -H "Content-Type: application/json" \
  -d '{"prompt": "Invoice Brandlink Agency ([email protected]) for 3 days of backend consulting at $1800/day, payment due in 30 days"}' \
  --output invoice.pdf

app.post("/webhooks/stripe", express.raw({ type: "application/json" }), async (req, res) => {
  const event = stripe.webhooks.constructEvent(
    req.body,
    req.headers["stripe-signature"]!,
    process.env.STRIPE_WEBHOOK_SECRET!
  );
 
  if (event.type === "checkout.session.completed") {
    const session = event.data.object;
 
    // Format Stripe data into invoice prompt
    const prompt = `
      Customer: ${session.customer_details?.name} (${session.customer_details?.email})
      Amount paid: $${(session.amount_total! / 100).toFixed(2)}
      Product: ${session.metadata?.product_name ?? "Software license"}
      Payment date: ${new Date(session.created * 1000).toLocaleDateString()}
    `;
 
    const invoiceData = await extractInvoiceData(prompt);
    const pdfBuffer = await renderInvoicePDF(invoiceData);
 
    // Email via Resend
    await resend.emails.send({
      from: "[email protected]",
      to: session.customer_details!.email!,
      subject: `Invoice ${invoiceData.invoiceNumber}`,
      html: "<p>Thank you for your purchase. Your invoice is attached.</p>",
      attachments: [{ filename: "invoice.pdf", content: pdfBuffer }],
    });
  }
 
  res.json({ received: true });
});

import { z } from "zod";
 
const InvoiceDataSchema = z.object({
  invoiceNumber: z.string(),
  issuedAt: z.string(),
  dueDate: z.string(),
  from: z.object({ name: z.string(), email: z.string() }),
  to: z.object({ name: z.string(), email: z.string() }),
  items: z.array(z.object({
    description: z.string(),
    quantity: z.number(),
    unitPrice: z.number(),
    total: z.number(),
  })),
  totalAmount: z.number(),
  notes: z.string().optional(),
});
 
const validated = InvoiceDataSchema.parse(rawLLMOutput);