Invoice Generator

The Invoice Generator skill automates the creation of professional, branded invoices in multiple formats (PDF, HTML, DOCX). It handles all standard invoice components including line items, tax calculations, discounts, payment terms, and company branding. Perfect for freelancers, agencies, and businesses that need to generate invoices programmatically.

Create invoices from templates, automate recurring billing, generate batch invoices for multiple clients, and maintain consistent branding across all billing documents.

Core Workflows

Workflow 1: Generate Standard Invoice (PDF)

Purpose: Create a professional PDF invoice with all standard elements

Steps:

• Collect invoice data (client info, line items, amounts)

• Calculate subtotal, tax, discounts, and total

• Load invoice template or create layout

• Add company branding (logo, colors, contact info)

• Populate invoice details (number, date, due date)

• Add line items table with descriptions and amounts

• Display payment terms and methods

• Generate PDF with proper formatting

Implementation:

const PDFDocument = require('pdfkit'); const fs = require('fs');

function generateInvoice(invoiceData, outputPath) { const doc = new PDFDocument({ margin: 50 }); const stream = fs.createWriteStream(outputPath); doc.pipe(stream);

// Company header doc.fontSize(20) .text(invoiceData.company.name, 50, 50) .fontSize(10) .text(invoiceData.company.address, 50, 80) .text(invoiceData.company.email, 50, 95) .text(invoiceData.company.phone, 50, 110);

// Company logo (if exists) if (invoiceData.company.logo) { doc.image(invoiceData.company.logo, 450, 50, { width: 100 }); }

// Invoice title and number doc.fontSize(24) .text('INVOICE', 400, 150, { align: 'right' }) .fontSize(12) .text(Invoice #: ${invoiceData.invoiceNumber}, 400, 180, { align: 'right' }) .text(Date: ${invoiceData.date}, 400, 195, { align: 'right' }) .text(Due: ${invoiceData.dueDate}, 400, 210, { align: 'right' });

// Bill to section doc.fontSize(12) .text('BILL TO:', 50, 150) .fontSize(10) .text(invoiceData.client.name, 50, 170) .text(invoiceData.client.address, 50, 185) .text(invoiceData.client.email, 50, 200);

// Line items table const tableTop = 250; doc.fontSize(10);

// Table header doc.fillColor('#2C3E50') .rect(50, tableTop, 500, 25) .fill() .fillColor('#FFFFFF') .text('Description', 60, tableTop + 8) .text('Quantity', 320, tableTop + 8) .text('Rate', 390, tableTop + 8) .text('Amount', 470, tableTop + 8);

// Table rows let currentY = tableTop + 30; doc.fillColor('#000000');

invoiceData.lineItems.forEach((item, index) => { const y = currentY + (index * 25); const bgColor = index % 2 === 0 ? '#FFFFFF' : '#F8F9FA';

doc.fillColor(bgColor)
   .rect(50, y, 500, 25)
   .fill()
   .fillColor('#000000')
   .text(item.description, 60, y + 8, { width: 240 })
   .text(item.quantity, 320, y + 8)
   .text(`$${item.rate.toFixed(2)}`, 390, y + 8)
   .text(`$${(item.quantity * item.rate).toFixed(2)}`, 470, y + 8);

});

// Totals section const totalsY = currentY + (invoiceData.lineItems.length * 25) + 30;

doc.text('Subtotal:', 380, totalsY) .text($${invoiceData.subtotal.toFixed(2)}, 470, totalsY);

if (invoiceData.tax) { doc.text(Tax (${invoiceData.taxRate}%):, 380, totalsY + 20) .text($${invoiceData.tax.toFixed(2)}, 470, totalsY + 20); }

if (invoiceData.discount) { doc.text('Discount:', 380, totalsY + 40) .text(-$${invoiceData.discount.toFixed(2)}, 470, totalsY + 40); }

// Total doc.fontSize(14) .fillColor('#2C3E50') .rect(380, totalsY + 60, 170, 30) .fill() .fillColor('#FFFFFF') .text('TOTAL:', 390, totalsY + 68) .text($${invoiceData.total.toFixed(2)}, 470, totalsY + 68);

// Payment terms doc.fillColor('#000000') .fontSize(10) .text('Payment Terms:', 50, totalsY + 120) .fontSize(9) .text(invoiceData.paymentTerms, 50, totalsY + 135, { width: 500 });

// Footer doc.fontSize(8) .fillColor('#7F8C8D') .text('Thank you for your business!', 50, doc.page.height - 80, { align: 'center', width: 500 });

doc.end();

return new Promise((resolve, reject) => { stream.on('finish', () => resolve(outputPath)); stream.on('error', reject); }); }

Workflow 2: Calculate Invoice Totals

Purpose: Automatically calculate subtotals, taxes, discounts, and final total

Steps:

• Sum all line item amounts for subtotal

• Apply discount (percentage or fixed amount)

• Calculate tax on discounted subtotal

• Compute final total

• Handle rounding to 2 decimal places

• Validate calculations

Implementation:

function calculateInvoiceTotals(lineItems, options = {}) { // Calculate subtotal const subtotal = lineItems.reduce((sum, item) => { return sum + (item.quantity * item.rate); }, 0);

// Apply discount let discount = 0; if (options.discountPercent) { discount = subtotal * (options.discountPercent / 100); } else if (options.discountAmount) { discount = options.discountAmount; }

const afterDiscount = subtotal - discount;

// Calculate tax let tax = 0; if (options.taxRate) { tax = afterDiscount * (options.taxRate / 100); }

// Calculate total const total = afterDiscount + tax;

return { subtotal: parseFloat(subtotal.toFixed(2)), discount: parseFloat(discount.toFixed(2)), discountedSubtotal: parseFloat(afterDiscount.toFixed(2)), tax: parseFloat(tax.toFixed(2)), taxRate: options.taxRate || 0, total: parseFloat(total.toFixed(2)), lineItemCount: lineItems.length }; }

Workflow 3: Generate from Template

Purpose: Use a branded invoice template for consistency

Steps:

• Load HTML/Word template with placeholders

• Define data mapping for template variables

• Replace placeholders with actual data

• Process line items loop

• Calculate and insert totals

• Convert to PDF or save as Word document

• Apply company branding automatically

Implementation:

const Handlebars = require('handlebars'); const puppeteer = require('puppeteer'); const fs = require('fs');

async function generateFromTemplate(templatePath, invoiceData, outputPath) { // Load template const templateHtml = fs.readFileSync(templatePath, 'utf8'); const template = Handlebars.compile(templateHtml);

// Register helpers Handlebars.registerHelper('currency', function(value) { return $${parseFloat(value).toFixed(2)}; });

Handlebars.registerHelper('multiply', function(a, b) { return (a * b).toFixed(2); });

// Prepare data const data = { ...invoiceData, currentYear: new Date().getFullYear(), formattedDate: new Date(invoiceData.date).toLocaleDateString(), formattedDueDate: new Date(invoiceData.dueDate).toLocaleDateString() };

// Render template const html = template(data);

// Convert to PDF const browser = await puppeteer.launch(); const page = await browser.newPage(); await page.setContent(html); await page.pdf({ path: outputPath, format: 'A4', margin: { top: '20mm', right: '20mm', bottom: '20mm', left: '20mm' }, printBackground: true }); await browser.close();

return outputPath; }

// Template example (invoice-template.html): /* <html> <head> <style> body { font-family: Arial, sans-serif; } .header { background: #2C3E50; color: white; padding: 20px; } .line-items { width: 100%; border-collapse: collapse; } .line-items th { background: #34495E; color: white; padding: 10px; } .line-items td { border-bottom: 1px solid #ddd; padding: 8px; } .totals { text-align: right; margin-top: 20px; } </style> </head> <body> <div class="header"> <h1>{{company.name}}</h1> <p>{{company.address}}</p> </div> <h2>Invoice #{{invoiceNumber}}</h2> <p>Date: {{formattedDate}} | Due: {{formattedDueDate}}</p> <h3>Bill To:</h3> <p>{{client.name}}<br>{{client.address}}</p> <table class="line-items"> <thead> <tr> <th>Description</th> <th>Qty</th> <th>Rate</th> <th>Amount</th> </tr> </thead> <tbody> {{#each lineItems}} <tr> <td>{{description}}</td> <td>{{quantity}}</td> <td>{{currency rate}}</td> <td>{{currency (multiply quantity rate)}}</td> </tr> {{/each}} </tbody> </table> <div class="totals"> <p>Subtotal: {{currency subtotal}}</p> {{#if tax}} <p>Tax ({{taxRate}}%): {{currency tax}}</p> {{/if}} <h3>Total: {{currency total}}</h3> </div> <p>{{paymentTerms}}</p> </body> </html> */

Workflow 4: Batch Invoice Generation

Purpose: Generate multiple invoices for different clients at once

Steps:

• Load client list with invoice details

• For each client:

• Prepare invoice data

• Calculate totals

• Generate invoice (PDF or other format)

• Save with unique filename

• Track generation success/failure

• Create summary report of all invoices generated

• Optionally send invoices via email

Implementation:

async function batchGenerateInvoices(invoices, outputDir) { const results = [];

for (const invoice of invoices) { try { // Calculate totals const totals = calculateInvoiceTotals(invoice.lineItems, { taxRate: invoice.taxRate, discountPercent: invoice.discountPercent });

  const invoiceData = {
    ...invoice,
    ...totals
  };

  // Generate filename
  const filename = `${outputDir}/invoice-${invoice.invoiceNumber}-${invoice.client.name.replace(/\s+/g, '-')}.pdf`;

  // Generate invoice
  await generateInvoice(invoiceData, filename);

  results.push({
    success: true,
    invoiceNumber: invoice.invoiceNumber,
    client: invoice.client.name,
    total: totals.total,
    filename: filename
  });
} catch (error) {
  results.push({
    success: false,
    invoiceNumber: invoice.invoiceNumber,
    client: invoice.client.name,
    error: error.message
  });
}

}

// Generate summary report const summary = { totalInvoices: invoices.length, successful: results.filter(r => r.success).length, failed: results.filter(r => !r.success).length, totalAmount: results .filter(r => r.success) .reduce((sum, r) => sum + r.total, 0), results: results };

fs.writeFileSync( ${outputDir}/batch-summary.json, JSON.stringify(summary, null, 2) );

return summary; }

Workflow 5: Recurring Invoice Generation

Purpose: Automate monthly/weekly recurring invoices

Steps:

• Load recurring invoice templates

• Check due dates for invoice generation

• For each due invoice:

• Clone template data

• Update invoice number (increment)

• Update dates (invoice date, due date)

• Generate new invoice

• Update next billing date

• Save invoice records

• Optionally send email notifications

Implementation:

function generateRecurringInvoices(recurringInvoices) { const today = new Date(); const generated = [];

recurringInvoices.forEach(template => { const nextBillingDate = new Date(template.nextBillingDate);

if (nextBillingDate <= today) {
  // Generate invoice
  const invoiceData = {
    ...template,
    invoiceNumber: generateNextInvoiceNumber(template.invoiceNumberPrefix),
    date: today.toISOString().split('T')[0],
    dueDate: calculateDueDate(today, template.paymentTermsDays)
  };

  const totals = calculateInvoiceTotals(invoiceData.lineItems, {
    taxRate: template.taxRate
  });

  generateInvoice({ ...invoiceData, ...totals }, `invoices/invoice-${invoiceData.invoiceNumber}.pdf`);

  // Update next billing date
  template.nextBillingDate = calculateNextBillingDate(
    nextBillingDate,
    template.frequency // 'monthly', 'weekly', 'quarterly'
  );

  generated.push(invoiceData);
}

});

return generated; }

function calculateDueDate(fromDate, days) { const dueDate = new Date(fromDate); dueDate.setDate(dueDate.getDate() + days); return dueDate.toISOString().split('T')[0]; }

function calculateNextBillingDate(currentDate, frequency) { const nextDate = new Date(currentDate); switch (frequency) { case 'weekly': nextDate.setDate(nextDate.getDate() + 7); break; case 'monthly': nextDate.setMonth(nextDate.getMonth() + 1); break; case 'quarterly': nextDate.setMonth(nextDate.getMonth() + 3); break; case 'yearly': nextDate.setFullYear(nextDate.getFullYear() + 1); break; } return nextDate.toISOString().split('T')[0]; }

Quick Reference

Action Command/Trigger

Generate invoice "create invoice for [client]"

From template "use invoice template for [client]"

Calculate totals "calculate invoice totals"

Batch generate "create invoices for [clients]"

Recurring invoice "generate recurring invoices"

Add line item "add item to invoice"

Apply discount "apply [%] discount"

Mark as paid "mark invoice [number] paid"

Best Practices

• Invoice Numbering: Use sequential numbers with a prefix (e.g., INV-2025-001)

• Due Dates: Clearly specify payment terms (Net 30, Net 15, etc.)

• Itemization: Provide detailed descriptions for each line item

• Tax Compliance: Apply appropriate tax rates based on jurisdiction

• Payment Methods: List all accepted payment methods clearly

• Contact Info: Include email and phone for billing questions

• Currency: Always specify currency (USD, EUR, etc.)

• Backup: Store copies of all generated invoices

• Versioning: Track invoice revisions if changes are needed

• Branding: Maintain consistent company branding across all invoices

• Legal Info: Include business registration numbers, tax ID as required

• Late Fees: Specify late payment penalties if applicable

• Accessibility: Ensure PDFs are readable by screen readers

Common Patterns

Freelance Invoice:

const freelanceInvoice = { company: { name: 'Your Name', address: '123 Main St, City, State 12345', email: 'you@example.com', phone: '(555) 123-4567' }, client: { name: 'Client Co.', address: '456 Client Ave, City, State 67890', email: 'billing@client.com' }, invoiceNumber: 'INV-2025-001', date: '2025-01-15', dueDate: '2025-02-14', // Net 30 lineItems: [ { description: 'Website Design - January 2025', quantity: 1, rate: 3000 }, { description: 'Consultation (5 hours)', quantity: 5, rate: 150 } ], taxRate: 0, // No tax for services in some jurisdictions paymentTerms: 'Payment due within 30 days. Accepted methods: Bank transfer, PayPal, Check.' };

Project-Based Invoice:

const projectInvoice = { lineItems: [ { description: 'Phase 1: Discovery & Planning', quantity: 1, rate: 5000 }, { description: 'Phase 2: Design Mockups', quantity: 1, rate: 7500 }, { description: 'Phase 3: Development', quantity: 1, rate: 15000 }, { description: 'Additional Revisions (8 hours)', quantity: 8, rate: 150 } ], discountPercent: 10, // Early payment discount taxRate: 8.5 };

Dependencies

Install required packages:

npm install pdfkit # For PDF generation npm install handlebars # For templating npm install puppeteer # For HTML to PDF conversion npm install nodemailer # For email sending (optional)

Error Handling

• Missing Data: Validate all required fields before generation

• Invalid Amounts: Ensure all monetary values are valid numbers

• Date Validation: Verify date formats and logic (due date after invoice date)

• File Permissions: Handle write errors when saving invoices

• Template Errors: Catch template rendering errors gracefully

• Currency Precision: Always round to 2 decimal places for currency

Performance Tips

• Cache company logo and branding assets

• Reuse PDF/template instances for batch generation

• Pre-validate data before processing

• Use streaming for large batch operations

• Compress PDFs for email transmission

Advanced Features

Email Invoice Delivery:

const nodemailer = require('nodemailer');

async function emailInvoice(invoiceData, pdfPath) { const transporter = nodemailer.createTransport({ /* config */ });

await transporter.sendMail({ from: invoiceData.company.email, to: invoiceData.client.email, subject: Invoice ${invoiceData.invoiceNumber} from ${invoiceData.company.name}, html: <p>Dear ${invoiceData.client.name},</p> <p>Please find attached invoice ${invoiceData.invoiceNumber} for $${invoiceData.total}.</p> <p>Payment is due by ${invoiceData.dueDate}.</p> <p>Thank you for your business!</p> , attachments: [ { filename: invoice-${invoiceData.invoiceNumber}.pdf, path: pdfPath } ] }); }

Payment Tracking:

const invoiceStatus = { invoiceNumber: 'INV-2025-001', status: 'unpaid', // 'unpaid', 'paid', 'overdue', 'cancelled' paidDate: null, paidAmount: 0, paymentMethod: null };