Demand Letter & Certified Mail Kit

When this helps

You want to chase overdue invoices in stages, but wording, records, interest and limitation dates take time to check each time

What it does

Groups overdue invoices by client and drafts each stage as Word and PDF letters: a confirmation request, demand letter, final notice, and certified mail (naiyo-shomei). It reads invoice and payment data straight from the Invoice Kit, formats certified mail to the post office's character and line rules, and writes the e-certified mail text too. Before sending, it flags wording that could read as a threat, missing details, and instruction-like text hidden in the data. It logs when letters were sent and received and how the other side replied, then rebuilds a collections ledger (Excel) tracking late-payment interest and limitation deadlines. It ranks what to do next for each client, and can also check a letter you drafted yourself.

The fixes baked into this kit

1. Overdue counting didn't match the real invoicing systemThe real invoicing system didn't count the due date itself as overdue. This kit now counts the delay from the day after the due date too, and checks the boundary between the due date and the next day with a self-test.
2. Couldn't record invoices with a partial paymentThe original invoicing system could only record full payments, but partial payments are common in collections. This kit now records partial payments and chases the remainder, applying any late-payment interest first and noting the amount applied in the letter.
3. Payment cancellations weren't counted as reversalsThe original system kept a payment cancellation as a record without removing it. This kit now counts a cancellation as reversing the matching payment.
4. Bank details stayed outdated after the account changedThe original system kept a copy of the bank details from when the invoice was issued, so if the account changed later the invoice still showed the old one. The first letter (confirmation request) now includes a line asking the client to confirm the bank details haven't changed.
5. A certified-mail rule on alphabetic characters tripped on invoice numbersJapan Post's certified mail rules only allow alphabetic characters in proper nouns, but invoice numbers (like INV-...) use them. The character-counting tool now accounts for this, and certified mail shows the invoice by its date and amount instead of its number.
6. Hit e-certified mail's page limit and character restrictionsOnline e-certified mail is capped at 5 pages, allows only a limited character set, and can't include tables or images. Pasted text is now plain paragraphs only, with a warning when it would exceed 5 pages or use an unusual character.

What's inside

• The flow (gather → draft → check → send → record → ledger)
• Staged letter drafts (confirmation request → demand letter → final notice → certified mail) as Word and PDF
• Certified mail formatted to the post office's character/line rules (naiyo-shomei), plus the text for e-certified mail
• Drafts for contract cancellation, debt acknowledgment, and installment agreements
• A tool that works out late-payment interest and limitation deadlines, with legal sources cited
• Pre-send checks for threatening wording, missing details, and instruction-like text hidden in the data
• A collections ledger (Excel) logging sent/received dates and replies, showing what to do next for each client
• Reads data from the Invoice Kit directly, without writing to it

The first three decisions

1. Sender details (company name, address, contact) and bank details
2. Whether to charge late-payment interest (default: no)
3. Payment deadline in days for each stage (default: 7 days)

What you need

• No extra costNode.js 18 or newerNeeded to run the tools. Nothing else to install.
• No extra costGoogle Chrome or Microsoft EdgeUsed to produce PDFs. If you don't have one, you can open the file in a browser and use "Save as PDF" instead.
• No extra costWord or Pages (for editing drafts)Used when you want to edit a draft by hand. Drafts still come out as finished PDFs without it.

How to use

Just paste this into your AI.

I want to use the nice to have kit "Demand Letter & Certified Mail Kit". Follow https://nicetohave.app/en/g/839LDVJ6-•••••••••• and set it up.

Works the same in Claude Code or Codex.
Read what this tells your AI to do, before you paste it

FAQ

Will it actually send the demand letters or certified mail?

No. A person sends them by email, post or e-certified mail. Once you tell it you've sent one, it logs that and locks the sent letter so it can't be altered.

What if the certified mail comes back undelivered?

Tell it the reason — for example, the recipient was out and the holding period expired — and it records the letter as returned, not as delivered. Check the address and recipient name; whether to resend another way is for your company and a professional to decide.

Can I use it for invoices from before April 2020?

Claims that arose on or before March 31, 2020 (including those under contracts made before then) fall under the pre-amendment Civil Code, so the kit does not calculate a limitation date or late-payment interest for them. Please check with a professional.

Can it tell me whether a claim is time-barred?

No. The expiry date it shows is only a guide. Whether the limitation period has run, or whether the other side can invoke it, is a question for a lawyer or judicial scrivener.

What if they still don't pay after the certified mail?

The kit only points you to court procedures such as a payment demand order or small-claims action; it does not prepare court documents. Decide how to proceed with a professional.

Supporters

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