Every week I opened a PDF editor, changed a few numbers, then checked the totals by hand. Days, discount, service fee, deposit, and the balance due. Miss one line and the invoice is wrong.
I turned that chore into a PDF invoice skill for my coding agent and open-sourced it. The public repo uses a fictional invoice, so you can run the workflow without anyone's real billing data.
The demo
The sample bills three event services by the day: setup, on-site coordination, and pack-down. A percentage discount comes next, then a 3% service fee on the discounted subtotal, then the paid deposit.
The clip starts at 3 days of on-site coordination and a 12.5% discount. Balance due: USD 1,254.65.
I sent this:
The client extended on-site coordination from 3 to 5 days. Give them a 15% discount instead, keep everything else the same, and open the updated invoice.The agent kept the daily rates and the deposit. It rewrote the day count, line amount, subtotal, discount, service fee, total, and balance. New balance: USD 1,691.76.
Try it
The code is in hqman/invoice-workflow.
Python 3.10+ and reportlab. Copy skills/invoice-workflow/ into your agent's skill folder, or open the project and tell the agent to read SKILL.md.
Read skills/invoice-workflow/SKILL.md. Use its fictional sample to generate a PDF. Show me the discount, service fee and balance due.Put names, day counts, rates, discount, and fee in JSON. The generator refuses to overwrite an existing PDF, so each revision gets a new file.
The folder is small: one SKILL.md, a JSON sample, and a script. I used the same pattern in the Humanizer skill post.
Limits
This skill draws a fresh PDF from JSON. It does not patch an arbitrary existing layout, and it does not copy metadata from an old invoice. Currency is a label, not a conversion. Tax and credit notes are out of scope.
If you have a stack of similar PDFs that need the same kind of number changes on a schedule, start from this sample and adapt the JSON to your template.