The specs are sort of published. There is this: https://www.gov.uk/government/publications/technical-interface-specifications-for-companies-house-software http

The specs are sort of published. There is this: https://www.gov.uk/government/publications/technical-interface-specifications-for-companies-house-software https://www.gov.uk/government/publications/technical-interfa... But none of those documents contain a complete specification. I followed various links, but couldn't find the actual schema for filing accounts. Some links look promising, but are dead. Perhaps there could be open source solutions, but as far as i know, there aren't. Nothing on this list looks open source: https://www.gov.uk/company-filing-software/filing-annual-accounts-returns-and-tax-accounts https://www.gov.uk/company-filing-software/filing-annual-acc... Dormant companies are indeed going to need to do this: https://companieshouse.blog.gov.uk/2023/02/10/changes-to-accounts-part-1-moving-to-software-only-filing/#comment-10517 https://companieshouse.blog.gov.uk/2023/02/10/changes-to-acc...