For your practice
- Ready on the day HMRC reopens filing access
- Client authorisation checked against HMRC itself
- Nothing sent to HMRC without a partner's ruling
Product
Connections
Cast & Rule connects to Xero, Microsoft 365, Companies House, HMRC and Dext. Each connection starts read-only and is tied to one client. Work also starts from records you supply.
The rules every connection follows
Every connection follows the same design. It reads before it writes, with the narrowest access each supplier offers. Each connection is tied to one client, and that's checked on every call. It can do a small, fixed set of named things, never open-ended access. It uses official interfaces or approved exports only. A partner rules on each exact action that would change an outside system. A connection on its own doesn't keep one client's records apart from another's, so each client's records also sit in their own encrypted store. Where a connection needs login details processed off the machine, we say so before use.
Rules before work
A clear brief. A firm boundary.
Which clients. Which sources. Which actions. Put the scope on the page before the work begins.
See the rules and safeguardsAnna Bennett FCANamed decision-maker
Awaiting partnerPartner sign-off
How each connection works
Read access comes first. If a connection needs to change something in an outside system, a partner rules on that exact action. The other way in is an export you supply.
Choose a connection to see what it does. On a keyboard, use the left and right arrow keys.
HMRC Making Tax Digital
Cast & Rule prepares the quarterly update for a partner to review. Your practice submits it through its existing MTD-recognised software.
Companies House
Reads public filing data (confirmation statement and accounts due dates, and filing history) to feed your deadline tracker. It uses public-register data only, and makes no filings.
Xero
The first connection. Read-only access to one Xero organisation per connection, through Xero's official interface. Any write, such as posting or adjusting entries, needs a partner's ruling on that exact action. Xero's own app terms and connection limits apply.
Microsoft 365
Read-only access to mail, calendar and files through Microsoft Graph, Microsoft's official interface, limited to what each task needs.
Dext
Receipts and invoices your clients capture in Dext, read-only, one client per connection.
Supported exports
Many practice systems export records, including ones with no public interface. The pilot starts from exports you supply, in the formats your software already produces.
1 of 6
Read as a list
All 6 connections lead into your practice: read-only, one client per connection.
- HMRC Making Tax Digital
- Cast & Rule prepares the quarterly update for a partner to review. Your practice submits it through its existing MTD-recognised software.
- Companies House
- Reads public filing data (confirmation statement and accounts due dates, and filing history) to feed your deadline tracker. It uses public-register data only, and makes no filings.
- Xero
- The first connection. Read-only access to one Xero organisation per connection, through Xero's official interface. Any write, such as posting or adjusting entries, needs a partner's ruling on that exact action. Xero's own app terms and connection limits apply.
- Microsoft 365
- Read-only access to mail, calendar and files through Microsoft Graph, Microsoft's official interface, limited to what each task needs.
- Dext
- Receipts and invoices your clients capture in Dext, read-only, one client per connection.
- Supported exports
- Many practice systems export records, including ones with no public interface. The pilot starts from exports you supply, in the formats your software already produces.
Built on request
We build a connector to your own systems
If your practice relies on a system that isn't shown here, we can build a custom connector to it on request, so Cast & Rule fits the tools you already use. It follows the same rules as every other connection: it reads first, it's tied to one client, and a partner rules on any action that would change that system.
This works where the system offers an API or an MCP server (a standard way for AI tools to connect) that we can be given access to.
Making Tax Digital
Ahead of the curve on MTD
HMRC publishes its own interfaces for Making Tax Digital. We build against them now, so Cast & Rule is ready for HMRC the day filing access reopens.
Nothing goes to HMRC without a partner's ruling.
What it is
HMRC's own interfaces
HMRC publishes its own interfaces for Making Tax Digital, with a test environment (its sandbox) that software makers build against.
A check on who you act for
One of them, the Agent Authorisation API, confirms which clients a practice is authorised to act for.
Filing needs HMRC's approval
Direct filing needs HMRC's approval, and HMRC has closed approval for new quarterly-update products for the 2026–27 tax year.
What we do
Build against HMRC's sandbox now
We build and test against HMRC's sandbox, ahead of filing access.
Check every client against HMRC
We use the agent-authorisation check, so Cast & Rule only ever works on clients your practice is authorised for, checked against HMRC's own records.
Apply for filing access when it reopens
We apply for filing access when HMRC reopens it. Until then, your practice's own HMRC-recognised software submits, after a partner's ruling.
Why it helps
Questions partners ask
Frequently asked questions
Which systems does Cast & Rule connect to?
Xero, Microsoft 365, Companies House, HMRC and Dext, each read-only first and tied to one client. Work also starts from an export you supply.
Why start with Xero read-only?
Read access proves the design (one client per connection, a fixed set of things it can do, every call recorded in the Ledger) before anything changes a client's system. Any write needs a partner's ruling on that exact action.
Does Cast & Rule submit to HMRC directly?
No. Direct filing needs HMRC's approval, and HMRC has closed approval for new quarterly-update products for the 2026–27 tax year. Cast & Rule prepares the quarterly update for a partner to check, and your practice's own HMRC-recognised software submits it after the partner's ruling. We build against HMRC's sandbox and apply for filing access when HMRC reopens it.
What happens if a connector fails?
Cast & Rule records failed and refused calls in the Ledger, as well as successful ones.
Does Cast & Rule work with IRIS or TaxCalc?
Through exports: work starts from the records IRIS or TaxCalc export. There's no direct connection to either.
One practice first
Start with one workflow, over six weeks, with us alongside
For a UK practice of 5 to 20 staff, with a partner who'll own the review. We run one workflow, measure it before and after, and agree in writing how it ends. Send an enquiry or email us today.