Stoneledger Rules Engine & API · for software companies and practices

Power your software with Stoneledger's CIS and accounting engines.

The UK's construction, VAT and tax rules, worked out to the penny and explained line by line - by the same tested engine Stoneledger's own product runs on, for your platform, your customers or your practice.

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Built, and closed for now: access is by agreement - there is no public sign-up.

An example answer

An invoice of£7,200labour £6,000, materials £1,200, 5% retention

Payable now£5,700after retention and CIS at 20%

And why

Every figure comes with its reason.

What it works out

Everything a construction or small-business platform has to get right.

Each of these is tested against HMRC's published rules, and offered only once it is.

CIS, both sides

The deduction on any invoice or payment - on the labour only, never materials or VAT - at the rate each subcontractor's status gives: 20%, 30% or gross
Worked out by payment, as HMRC counts it: part payments, payments across a month end and retention released later each land in the right tax month
Retention held back and released, with the deduction on each release
Each month's CIS300 figures, subcontractor by subcontractor
What every payment and deduction statement should say - and whether one you were given agrees with what was paid
The penalties a late CIS300 return builds up, month by month
The tax month any date falls in, and when its return and payment are due

VAT and Making Tax Digital

Whether the construction reverse charge applies to a supply, and why - end users and intermediaries included
The VAT on a CIS invoice when both, one or neither business is VAT registered
Whether, and from when, Making Tax Digital for Income Tax applies, from qualifying income across self-employment and property

Tax, and getting paid

Income Tax and National Insurance on self-employed profit, each part explained
Corporation Tax, with marginal relief and associated companies
Tax on dividends, beside other income
Statutory interest and fixed compensation on a late business invoice

Every answer gives its reasons line by line, names the tax year whose rates it used, and is the same every time for the same figures.

And behind Stoneledger

The same engine runs a whole UK accounting product.

Stoneledger's own product works out far more than the list above. None of this is offered outside Stoneledger yet - tell us what you need, and what opens next follows what is asked for.

Returns and payroll

VAT returns under the standard, cash accounting and flat rate schemes, with HMRC's periods and due dates
Payroll: PAYE, National Insurance and payrolled benefits, and the figures for each Real Time Information submission
Self Assessment for the self-employed and landlords, from the books to the return

Property and companies

Rental income, with finance costs, and furnished holiday lets after April 2025
Corporation Tax computations, with losses carried between years and short accounting periods
Dividends, directors' loans and the tax on a loan left unpaid

The books and the accounts

Fixed assets, depreciation and capital allowances
Trial balance checks, and the figures for a company's statutory accounts
A reason behind every figure, from the total down to the entry

What you get

Something you can put in front of your own customers.

Access by agreement

Separate test and live access for each organisation
Limited to the calculations agreed
Changed or ended at any time
A volume of use agreed with you

Answers you can rely on

The same figures always give the same answer
What you receive keeps its form - a change comes as a new version, with notice
Rates and thresholds checked against GOV.UK before each tax year
Test answers exactly as live ones

Your customers' data

Figures in, answers out: no names or bank details needed
Requests answered, not kept - only a count of use
Every access given and ended, on record
Run from Stoneledger's servers in the UK

Pricing

Licensed by agreement, to fit how you would use it.

Monthly licence

A set monthly fee for an agreed volume of use.

By usage

Paid for by what is used, for a platform whose volume moves month to month.

Practice licence

For an accountancy practice using the calculations across its own clients.

White-label or enterprise

The engine inside your own product, under your name, on a contract of its own.

No price is published until the hosting, volumes, support and liability behind it have been worked out properly. Tell us what you would build, and the terms follow from that.

Request access

Tell us what you would build.

We read every request and reply from a real inbox. Fields marked * are required.

Your name *

Email address *

Organisation *

What kind of organisation? (optional)

Website (optional)

How many customers or clients would use it? (optional)

What would you use it for? *

Questions

What developers ask first.

Can I start using it today?

Not yet. It is built, and opens to organisations outside Stoneledger by agreement, once the security, documentation, support and licensing for each are in place. Request access and you will hear first.

Can we see it working first?

Yes. Once we have talked through what you would build, we will show it answering examples of your own.

Where do the rules come from?

From HMRC's published rules and rates, kept current and checked against GOV.UK before each tax year. Every answer says which tax year's rates it used.

Will you keep our customers' figures?

No. A request is worked out and answered; its figures are not kept. What is kept is a count of use, for limits and billing, and a record of each access given and ended.

Can it send returns to HMRC?

No. It calculates and checks; it does not file anything with HMRC or Companies House.

Is there a test environment?

Yes, for each organisation given access, answering exactly as live access would.

Is it advice?

No. It applies published rules to the figures it is given and explains each step; the software and the business using it stay responsible for what they do with the answer.

Specialist UK rules, without building them yourself.

Tell us what you would build. Or, if your customers are construction businesses, a partnership may suit better.

Request API access Partnerships

The engine applies published HMRC rules to the figures given to it; it is not tax advice.