Plumbing Invoice Generator App Template for iOS

A plumbing invoice app does one job well: it turns a finished repair into a clean, signed invoice on the spot. That means line items for labor and parts, computed tax and totals, a few job photos as evidence, a signature, and a PDF the customer can keep. VP0 is the free, AI-readable iOS design library trades builders start from for these screens, so you can wire the logic instead of designing invoice layouts from zero.

Who this is for

You are building a field-service app for plumbers, electricians, or HVAC techs, on your own or with Cursor or Claude Code, and you want an invoice flow that is reliable, offline, and honest about what it is. This is that pattern.

Offline-first or it loses work

The defining constraint of trade apps is signal. Technicians work in basements and crawl spaces, so anything that needs a connection to save will eventually lose an invoice. Store everything locally first with SwiftData or Core Data, let the tech finish and sign offline, then sync to the office when a connection returns. This is the same offline-first discipline behind a construction site daily log, where the record has to survive a dead zone.

What to compute and what to never free-type

An invoice is a record, so the math must be reproducible. Store each line item as a quantity and a unit price, then derive everything else. Never let someone hand-type a total.

Invoice field	How it should work	Why
Line item	Quantity times unit price	Editable inputs, computed amount
Subtotal	Sum of line amounts	Derived, not typed
Tax	Rate applied to subtotal	One source of truth for the rate
Total	Subtotal plus tax	Read-only on screen and PDF
Photos	Attached to the job	Evidence for the work done
Signature	Captured on device	Acknowledgement, not legal advice

Computed fields mean the PDF and the screen always agree, which is what prevents disputes later.

The signature and the PDF

Capture the customer acknowledgement with PencilKit, then render the whole invoice to a shareable file with PDFKit. A PDF is the right format because it prints, emails, and archives the same everywhere. Keep the signature framed as an acknowledgement of work done, not as legally binding advice, the same honesty a DocuSign-style signing flow needs. The PDF is the deliverable the customer keeps and the office files.

Be honest about payments and tax

Two boundaries keep you safe. First, you are not a payment processor: route money through a certified provider like Stripe or Square, or a card reader SDK, so you never store card data and stay out of the heaviest PCI scope. Second, you are not an accountant: the app records what is owed, it does not give tax advice, and the tax rate is configured by the business. The field-service software market is worth over $5 billion and growing, so the opportunity is real, but the credibility comes from staying in your lane. Scheduling those jobs is its own screen, handled well by a drag-and-drop shift calendar.

A worked example: a Saturday call-out

A plumber finishes a burst-pipe repair in a basement with no signal. In the app, they add two line items: 1.5 hours of labor at a saved rate, and one replacement valve at its part price. The subtotal updates as they type, tax applies automatically, and the total stays read-only. They snap two photos of the finished joint, hand the phone to the customer for a signature, and tap Generate PDF. Everything saved locally, so none of it depended on a connection. Back in the van with signal, the app syncs the invoice to the office and emails the PDF to the customer. The whole interaction took two minutes and produced a clean, photo-backed record that is hard to dispute. A dispatcher view that maps the next job reuses the live-location patterns of a dog-walking GPS tracker.

Common mistakes and fixes

• Requiring a connection to save. Store locally first and sync later.
• Free-typing totals. Compute every derived field from line items.
• Handling card numbers yourself. Use a certified provider and never store cards.
• Treating the signature as legal proof. Frame it as an acknowledgement.
• Forgetting photos. Job photos cut disputes and document the work.

Key takeaways

• Build offline-first so a basement never costs the tech an invoice.
• Compute totals from line items; never let anyone type a total.
• Export a PDF with PDFKit and capture a signature with PencilKit.
• Route payments through a certified provider, and start from a free VP0 design.

Frequently asked questions

The FAQ above covers where to find a free template, computing versus typing totals, taking payments safely, and why offline support is essential.