This note follows HMRC's Guidelines for using generative artificial intelligence if you're a software developer (28 January 2026). It describes declownify as designed for its first release.

Status: not built yet. The rules audit is part of the design for the first release, but it is not in any build of declownify yet. This note sets out the limits it must meet. The audit will not ship in any release until the code enforces every one of them.

• declownify has one AI feature: an optional rules audit. It is off until you set it up.
• The AI never sees your company's data. It sees only declownify's own source code and its table of tax rules.
• The AI never computes a tax figure. Every figure in your return, accounts and computation is calculated by ordinary, deterministic program code.
• The AI never changes anything. It reports possible problems. A person decides what to do about them.

• Tax figures. Profits, allowances, losses, tax, marginal relief, s455 tax and every CT600 box are computed by fixed rules in the Rust code. The same books always give the same return.
• Accounts and computations. These are built by program code from the same figures.
• Validation and filing. Validation uses HMRC's own schemas and business rules, and the IRmark is calculated to HMRC's specification.
• Receipt search. This is a database search of your local mailbox copy, matching on dates, amounts and senders.
• Reminders. Reminder emails, calendar events and notifications are written from fixed templates and sent through your own email and calendar. No reminder passes through an AI assistant. If a route through an AI assistant is ever added, it will be off unless you switch it on, and this note will say first what it sends.

What it is for. Every rate, threshold, deadline and penalty that declownify uses is kept in one table. Each entry records its value, the primary source it comes from (GOV.UK guidance, legislation or HMRC manuals) and the date it was last checked. The audit asks an AI assistant to check each entry against its cited source and to report:

• entries that no longer match their source;
• entries whose check date is old;
• points where sources disagree.

Which assistants. You choose one, or two for a cross-check:

• Claude Code (Anthropic), run as a program installed on your computer under your own account;
• Codex CLI (OpenAI), likewise;
• Z.ai (Zhipu GLM), called over its API with your own key.

The provider bills its use to your account. You can set a spending limit.

What the assistant receives. declownify's own source code and its rules table, as published in the release you run. They hold no taxpayer data. declownify builds the audit request from those alone; it never adds your books, files or settings. If you allow web access for the audit, the assistant may read public pages such as GOV.UK and legislation.gov.uk to check a source.

What it never receives:

• your books, bank statements, receipts or emails;
• your company's name, number or UTR;
• your returns or any figure in them;
• your Government Gateway or other credentials;
• any other personal data.

How results are used.

• Checked shape. The assistant must answer in a fixed, structured form, which declownify checks before using.
• Disagreements go to you. If you run two assistants and they disagree, or the audit disagrees with a rule, declownify shows you a task with the rule, both answers and their sources. You decide.
• Rules change only by release. An audit result never changes a rule or a figure by itself. A rule changes only in a new release of declownify, after a person has reviewed the source.

When it runs. You can run it on demand. Once it is set up, it can also run in the scheduled background check, within your spending limit.

AI assistants can be wrong. They can state plausible things that are false (so-called hallucinations), miss a recent change, or misread a source. The audit is an extra check on the product's rules, not a source of truth. HMRC publications, legislation and case law remain the authority.

You are responsible for making sure your company's tax return is accurate. Check the figures before you approve a return. Where declownify flags a rule as uncertain, or your affairs are complex, investigate further or take advice from a qualified tax adviser.

The audit runs only if you have set up an assistant in declownify's integration settings or configuration. To stop it, remove the assistant there. Everything else in declownify works the same without it.

HMRC does not endorse or approve any software developer or product, and declownify does not act on behalf of HMRC (see the independence disclaimer).

Questions or problems with the audit: letsmallbusinessesfiletheirowntaxes@okashi.school