Internal Tool · Document Automation
The Billing System I Run My Own Invoicing On
Rather than track hours in Apple Notes and hand-build invoices, I built a local-first billing app: log time, generate the invoice, and produce the Hungarian compliance certificate — automatically. It's run dozens of real billing cycles.
Dozens
Real billing cycles run through it
0.25h
Time tracked to the quarter-hour
Invoice + cert
Generated, not hand-built
HU-compliant
Completion certificate auto-produced
What this means for you
I run my own business on the systems I sell. If your invoicing or compliance paperwork is still assembled by hand every cycle, this is the shape of the fix — small, unglamorous, and it never misses a period.
The Problem
My own client billing was the exact kind of admin I automate for other people: hours tracked in Apple Notes, invoices assembled by hand each period, and — because this is Hungarian B2B — a separate compliance certificate to produce for every one.
It was small, repetitive, and easy to get slightly wrong. So I did the thing I'd tell any client to do: I turned it into software.
The Solution
A local-first billing app. I log time to the quarter-hour; when it's time to invoice, it gathers everything uninvoiced, draws down any prepaid-hour balance first, bills the remainder, and renders both the invoice and the Hungarian certificate of completion to PDF — ready to send.
Log Time
Apply Prepaid Hours
Generate Invoice
Compliance Certificate
Track Sent / Unsent
What It Does
Prepaid balances, handled correctly
Retainer-style prepaid hours are consumed first, automatically, and only the net remainder is billed — the fiddly part of retainer accounting that's easy to miscount by hand.
Compliance paperwork, generated not typed
The Hungarian "Teljesítési Igazolás" — a certificate every completed period needs — is produced as a finished PDF from a template, not retyped each time.
Knows what's been sent
Sent/unsent status is tracked per period, so the next billing window is picked up automatically — no "wait, did I already invoice that?"
Why This One Matters
It's a small tool, but it's the honest kind of proof: the systems I build for myself are the systems I build for clients. If I won't do my own repetitive admin by hand, I'm not going to leave yours that way either.
Tech Stack
| Layer | Technology |
|---|---|
| Application | Python web app — single local-first codebase |
| Data | SQLite — time entries, invoice periods, prepaid-hour balances |
| Documents | LibreOffice headless — renders invoices + certificates to PDF from templates |
| Compliance | Auto-generated Hungarian “Teljesítési Igazolás” (Certificate of Completion) |
Let's Talk
I take on 3 new clients per month.
The businesses that move first win. Let's find where you're leaving 20+ hours a week on the table.
Book Your Free Audit● Capped at 3 new clients per month — the audit call is how you claim a slot