declownify is being built to keep the books, work out the tax and prepare the CT600 with its iXBRL accounts and computation, then file them with HMRC, all from your own computer.

• In development. No version has been released, so there is nothing to install yet. The download page says what is coming.
• Not HMRC recognised. We will apply for HMRC recognition once declownify passes HMRC's test services. We will call it HMRC recognised only once it appears on GOV.UK's list of commercial software suppliers for Corporation Tax.
• Companies House filing is planned. The first release will prepare the accounts for HMRC. Filing them with Companies House comes later.
• macOS and Linux. A macOS app and a Linux command-line program are being built on one shared Rust core. A web interface is planned.

HMRC's "File your accounts and Company Tax Return" online service (often called CATO) closed on 31 March 2026. Since 1 April 2026 a company should file its Company Tax Return using commercial software, and a paper return is allowed only with a reasonable excuse or in Welsh (GOV.UK). From April 2028 Companies House will require all companies to file their accounts through software too (GOV.UK).

declownify is for the director of a very small company who keeps the books and wants to file the return themselves.

Keep the books. Import bank statements, record transactions, and find candidate receipts in a local, read-only copy of your own mailbox.

Work out the tax. Accounting periods, including a first period longer than 12 months, which needs two returns. Small profits rate, marginal relief, capital allowances, losses and s455 tax, from fixed rules that each cite their source.

File with HMRC. Check the return against HMRC's schemas and rules, run a Test in Live check, and submit only after the director approves it. Keep HMRC's receipt.

declownify is for directors of micro-entity private companies limited by shares, with one trade, who file their own returns. Other small companies (FRS 102 Section 1A accounts) are planned. It is not built for agents filing for clients.

The feature matrix lists what is in scope, what is planned and what is not supported. Its first user will be OKASHI SCHOOL LIMITED, which makes it.

1. Prepare. Books, then accounts, then computation, then the CT600.
2. Validate. The return is checked against HMRC's CT600 schema and business rules. The CT600 boxes are cross-checked against the computation, and the company number, UTR and period end across all three documents. Then the IRmark is computed.
3. Approve. The director reads HMRC's declaration word for word and types their name and status.
4. Test in Live. The same return goes to HMRC's live service as a test. HMRC checks the login and the business rules without registering the return.
5. Consent. You type "I CONFIRM LIVE SUBMISSION". Without it, the code cannot build a live submission.
6. Submit. declownify submits over HTTPS, polls no sooner than HMRC asks, saves HMRC's response and then deletes HMRC's copy, as the protocol requires. It never resubmits on its own.
7. Receipt. declownify checks the IRmark in HMRC's signed receipt against the one it sent, and shows every HMRC message word for word.

There is no declownify server and no account with us. Return data leaves your computer only when you submit to HMRC (and, once that is built, to Companies House). Reminder emails, if you switch them on, go out through your own email account. Your Government Gateway login is never logged and never sent to an AI service.

The privacy policy and the security statement give the detail.

The only AI feature is an optional rules audit, designed but not yet built. An AI assistant you choose checks declownify's own table of tax rules against the sources each rule cites. It is designed never to receive your books, your returns or any personal data, and no AI computes any figure in your return. The note on the use of AI sets out its limits.

declownify is independent software from OKASHI SCHOOL LIMITED. It is not provided by, endorsed by or affiliated with HM Revenue & Customs (HMRC) or Companies House, and it does not act on behalf of either. HMRC does not recommend or endorse any one software product over another and does not support commercial software, and Companies House does not endorse or recommend particular products: please send any question about declownify to OKASHI SCHOOL LIMITED at letsmallbusinessesfiletheirowntaxes@okashi.school. You remain responsible for the accuracy of your company's tax return.

declownify is not HMRC recognised.

Security, privacy, terms, accessibility, the use of AI and the full scope.