Since May 2026, Anthropic's Claude for Small Business plugin has given paid Claude plans a bundle of ready-made skills. One of them chases invoices: it ranks what is overdue and drafts a reminder for each, matched to how that customer has paid before. It reads Xero, QuickBooks and other ledgers, and nothing goes out until you say so. It costs nothing on top of a Pro, Max, Team or Enterprise plan, and Anthropic describes every task as started by you. That is a good product, and if it is enough for you, use it.
Harness is a different kind of thing: a business brain that works with the whole business and simplifies everything it touches. It keeps one memory of how your business runs, outside any single chat, and works through the night without being asked. It follows the money you are owed and the quotes that went quiet, names the email you should not act on, and gives each person on the team a role. It runs inside the ChatGPT or Claude you already pay for, it is built for UK firms, and you are early to it.
The plugin gives you skills to run. Harness is a business brain: it keeps one memory of the business and has the queue ready before you open the chat.
If your books are in a ledger the plugin connects to, you are happy working inside Claude Cowork, and all you want is a drafted reminder for each overdue invoice, the plugin does that at no extra cost. Try it before you pay anyone, including us.
If unpaid quotes cost you as much as unpaid invoices, if a team needs roles, if you want the email you should not act on named for you, or if you use ChatGPT as well as Claude, that is the job Harness does. It sits inside the same chat you already open.
There is no extra charge for the Claude for Small Business plugin on a Pro, Max, Team or Enterprise plan, according to Anthropic's install tutorial. You still pay for the plan itself. Harness runs on that same plan, or on a ChatGPT plan, for £19 a month on top.
Yes. Xero is one of the connectors Anthropic names for the plugin, alongside QuickBooks and others, and the plugin asks before anything sends. Harness reads Xero too, so the ledger is parity. Harness is built around one memory of the business that it works through overnight, with quiet quotes alongside invoices, the email you should not act on, and roles for the team.
One memory of how your business runs, kept in Harness rather than in any one chat: the facts read from your books and inbox with where each came from, the rules you have set, and a record of what was approved and sent. Harness works on that overnight and has a queue ready in the morning. Because the memory is not tied to one chat, it stays put if you switch between Claude and ChatGPT.
We could not find a quote follow-up skill in the published plugin. Its invoice-chase skill is for overdue invoices. Harness treats a quiet quote as a follow-up and an overdue invoice as a chase, and keeps the two apart.
Before it drafts, Harness checks the ledger again for a payment that landed overnight, checks whether this customer was chased in the last seven days, checks for an open dispute, and reads how the customer normally pays. A customer who always pays on day 40 is not chased on day 35.
Drafts wait for you to approve, edit or skip. You can let routine reminders send on their own, and only those. The approval is bound to the exact text, so a draft that changes after it is staged does not go.
Yes. Harness is an MCP server you add to Claude or ChatGPT, so it sits alongside anything else in that account. Keep the plugin for the skills you start yourself, and add Harness for the business brain, the quotes and the team.
Connect Xero and your inbox, and tomorrow morning there is a queue of chases and quote follow-ups waiting for your tap, in the chat you already use. Seven days free.