William doesn't start from scratch. It arrives with UK VAT rules built in from HM Revenue and Customs (HMRC), and the moment you connect your ledger, it keeps learning – your chart of accounts, your historical documents, how your firm codes transactions. Every correction sharpens it further.
You can make William learn fast, giving direct instructions about your firm’s specific policy. Guidance is a plain-English instruction that William follows on every new document. Write it the way you'd brief a new team member.
Quick start
Go to William AI > Guidance > Add guidance, type Taxis such as @Uber and @Bolt go to @Travel and click Save. Type @ to pick the exact supplier, category or tax rate from your ledger. William follows this on all future documents.
How guidance works
Guidance is a plain-English instruction that tells William exactly how your firm wants things done. Write it the way you'd brief a new team member.
Guidance can set or change:
Category
Tax rate and VAT amount
Total
Invoice number
Issue date and due date
Description
Tracking categories
Line items, by grouping and coding them
Whether a document is auto-published
Guidance isn't tied to one document. Even if you write it while looking at a document, William uses it on every new document for that company where it's relevant.
Guidance is set per company. Currently, there's no place to set up guidance at the practice level, so to use the same guidance for another company, add it to that company, too.
Are there restrictions?
Currently, Guidance works on the fields of a document, on line items when you ask explicitly, and on auto-publish. For these jobs, use a different tool:
Matching supplier contacts – Supplier rules set the contact; guidance shouldn't be relied upon to reassign suppliers.
Converting currencies – If a receipt shows foreign currency, William cannot calculate the exchange rate into GBP. (If an invoice shows multiple currencies, you can guide William on which one to select.)
Editing line-item amounts or quantities – Guidance can split, merge, or group line items, but it cannot alter individual line values like quantity, unit price, or line totals.
Bank statements and sales invoices – Guidance applies to bills and receipts. It isn't used for bank statements.
Assigning a document to a customer – Assign customers directly on the document view.
Inbox management or ledger actions – Guidance cannot archive, delete, split, or merge files, manage email search, or trigger actions directly inside Xero or QuickBooks.
Reading poor-quality images – Guidance cannot fix blurry, cropped, or unreadable receipts; upload a clearer copy instead.
Supplier rule or guidance?
Set a supplier rule when the answer's the same on every document from one supplier. Use guidance when it depends on what's on the document, or applies to many suppliers. You can use both for the same supplier: fixed fields go in the supplier rule, everything else in guidance.
If you want to… | Use |
Use the same category, tax rate, payment terms or description every time | Supplier rule |
Always publish everything from one supplier | Supplier rule |
Pick a category based on what was bought | Guidance |
Set VAT based on what the receipt shows | Guidance |
Add changing details to the description, such as the invoice number or billing period | Guidance |
Hold back statements, pro formas or delivery notes | Guidance |
Supplier rules are set as fixed rules. You can add them from Settings > Contacts, from William AI > Guidance > Fixed rules, or from a document in your Inbox by clicking Add fixed rules. Find out more in our article: Create contact and supplier rules.
How William decides
William uses what it knows in this order:
Company defaults – always applied first, and they overwrite other predictions.
Guidance – your plain-English instructions.
Your history – documents you've already published for this company. If your history points the other way, William may need two or three corrections before it switches.
Company defaults set under the Advanced bookkeeping section or the contact rules are always applied and take priority over any other rules, such as guidance or history.
Tip: William needs a few published documents before it starts suggesting guidance, but you don't need to wait. Add two or three pieces of guidance to set your main policies from day one. If you keep making the same correction, add guidance instead.
Suggestions from William
When William spots a pattern in your corrections, it suggests guidance for you. You'll find suggestions in the Suggestions tab in your Inbox. There are two kinds:
Proposed guidance – a rule William thinks you'd want, such as Everything from Uber goes to Travel. Accept it, add detail first, or reject it.
Open question – something William isn't sure about, such as What category applies to Vodafone? Your answer becomes guidance.
Each suggestion shows the documents it's based on. Nothing changes until you accept or answer it, and accepted suggestions appear on the Guidance page, where you can edit or remove them. If you reject a suggestion and change your mind, you can add the same guidance yourself.
Good to know
Guidance applies only to documents uploaded after you save it. To change a document that's already in your Inbox or published, edit the document directly.
Supplier rules also update that supplier's documents waiting in your Inbox, whether active or in draft, but not deleted, archived or published ones.
Guidance is set per company. To use the same guidance for another company, add it there too.
What's next
Write guidance William can follow – how to add guidance and word it so William gets it right.
See examples of guidance – copy-paste examples for VAT, Construction Industry Scheme (CIS), descriptions, dates, line items and publishing.
Fix guidance that isn't working – check that guidance worked, and what to try if it didn't.