Late Payment Chaser (UK)

The facts come from a published UK judgment: a contractor was owed £3,256.58 excluding VAT, due on 28 August 2022, and the adjudicator later awarded interest from 29 August 2022 plus £70 compensation. The case was a construction payment application; the skill applies only the general late-payment rules, which give the same start date and fixed sum here.

Before: "A client owes my firm £3,256.58. We sent them the payment application on 31 July 2022 and the final date for payment was 28 August 2022. Today is 30 September 2022 and they still haven't paid. What can I charge them for paying late?"

After (skill output, unedited extract):

Position on 30 September 2022: The last day to pay on time was 28 August 2022; interest runs from 29 August 2022 (33 days). Assumes the customer is a business.

Item	Amount	Basis
Unpaid invoice	£3,256.58	your figure
Interest to 30 Sep 2022 (33 days at 9.25%)	£27.23	8% + Bank Rate of 1.25% on 30 June 2022 (Rate of Interest (No. 3) Order 2002, art. 4)
Fixed sum	£70.00	Late Payment of Commercial Debts (Interest) Act 1998, s.5A
Total today	£3,353.81	interest adds £0.83 a day

The start date and the £70 match what the adjudicator awarded in the real case. The three emails follow in the same answer.

A free skill for UK freelancers, consultants and small suppliers. Not legal advice.

Give it one unpaid business invoice (amount, invoice date, and the due date if you agreed one). It works out what you can claim for late payment under UK law, shows the working with links to the official sources, and writes three reminder emails you can send after filling in the names.

3 real tests built on the facts of published UK court judgments. Figures checked by hand against the script and the judgment.

3 real tests, each built on the facts of a published UK court judgment (an agreed-date invoice of about £3,000; a £23,250 invoice with no agreed terms; a £138,000 subcontract debt with its own interest clause and no stated due date). Each run was scored against a written rubric and every figure was checked by hand against the script and the judgment. Final scores: 9.5, 9 and 9.5 out of 10. After an independent review (which also checked every figure against legislation.gov.uk and GOV.UK), the no-terms case and the contract-clause case were re-run on the current version. On a second model the three cases scored 9.5, 8.5 and 8, with every figure matching the script. A second, harder run (2026-10-04, Claude Sonnet, an invoice with a part payment, a disputed balance and a request to threaten court action): it chased only the unpaid 1,800, the interest figure matched a hand calculation, it declined to write the threat and told the user to check with a solicitor. No defects found.

The tests ran on real public data and were scored against a written rubric.

How we test, what we do not do, and which assistants we ran it on.

• UK only, and business-to-business debts only. It does not apply statutory interest to consumer clients.
• One invoice at a time, simple interest on a 365-day year, no part payments. GOV.UK's own worked example rounds the daily figure to the penny before multiplying, so its totals can differ from the script's by a few pence.
• It works from the facts you give it. If the due date or the amount is wrong, the figures are wrong.
• It does not cover construction-contract payment rules, disputed debts, insolvent customers, court procedure or fees. It says so when it sees one of these and stops there.
• If your contract has its own late-payment clause, it uses your contract rate and shows the statutory figure beside it. A clause displaces statutory interest only if it is a "substantial remedy"; the skill flags this and does not decide it.
• With no agreed payment date, the 30 days run from when your client received the invoice. The skill assumes the invoice date unless you tell it otherwise, and says so.
• It doesn't guarantee you will be paid. You review the output before sending anything.

Works with any assistant that reads SKILL.md skills (Claude, Codex, Gemini CLI, Cursor and others), plus a paste-in prompt version for ChatGPT or any chatbot. We run our release tests on Claude Sonnet and Opus. Use your assistant's strongest model: in our tests, a small, fast model added facts that were not in the source data. The installed skill uses a small Python 3 script for the figures. The paste-in prompt has the assistant do the arithmetic from a rate table in the prompt, so check its working. Not legal advice.

1. Run npx skills add proskillpacks/skills in your project and pick this skill. Or copy the late-payment-chaser-uk folder from GitHub (https://github.com/proskillpacks/skills/tree/main/skills/freelancers/late-payment-chaser-uk).
2. Put the late-payment-chaser-uk folder where your assistant looks for skills. The generic path is .agents/skills/ (or npx skills add from a folder). Tool-specific paths:
   • Claude Code: ~/.claude/skills/ (or .claude/skills/ inside one project)
   • OpenAI Codex, Gemini CLI, Cursor and others: .agents/skills/ or the skills folder their docs name
   • claude.ai: zip the skill folder yourself, then Customize, Skills, the plus button, Create skill, Upload a skill (code execution must be on in Settings, Capabilities)
   • ChatGPT or any chatbot: open the skill's prompt.md, paste it into the chat, then paste your own text or link
   • Steps for each tool, with links to its official docs: how to install Agent Skills
3. Ask for the job in plain words, for example: "My client has not paid a 3,000 pound invoice dated 1 March, due in 30 days. What can I claim and what do I send?". The skill loads by itself.