Add Norway (NO) tax regime

[0xjgv]

We chose Norway as the next tax regime through a repeatable analysis: we audited all supported and upcoming countries, scored gaps against economic potential weighted by Invopop's customer base, and narrowed to three. Norway ranked highest for regulatory clarity, manageable scope, and iteration speed. That said, this approach is second to the one driven by customers' needs.

Add full Norwegian tax regime implementation, including VAT support, organisasjonsnummer validation, simplified invoice handling, and invoice type handling.

• Norwegian VAT regime with four tax rates: general (25%), reduced (15%), super-reduced (12%), special (11.11%)
• Historical rate values for super-reduced rate (6% from 2004, 7% from 2005, 8% from 2006, 10% from 2016, 12% from 2018, 6% COVID reduction Apr 2020, 12% restored Oct 2021)
• Bilingual (EN/NB) descriptions for all rates
• Organisasjonsnummer (org.Identity type ON) with mod-11 check digit validation per Brønnøysundregistrene spec
• Tax identity normalization stripping NO prefix and MVA suffix
• Simplified invoice support: relaxes supplier address and TaxID requirements, customer is optional (following the SE pattern)
• Supplier TaxID intentionally optional — Norwegian businesses below NOK 50,000 turnover are not VAT-registered but may still issue invoices
• Invoice validation: supplier name required (address required for standard, optional for simplified), customer name required on standard invoices
• Credit note and debit note correction types requiring preceding document reference
• Norwegian (nb) translations alongside English
• Regime description field using here.Doc (following FR pattern)
• Six example invoices: standard domestic, multi-rate, simplified, reverse-charge, credit note, debit note

Sources

• Skatteetaten - VAT rates
• Brønnøysundregistrene - Organisation number
• Lovdata - Merverdiavgiftsloven
• Altinn - Invoice requirements
• St.prp. nr. 1 (2005-2006) — Historical rate confirmation
• St.prp. nr. 1 (2006-2007) — Historical rate confirmation

Out of Scope

Deliberately excluded from this PR (documented in README):

• SAF-T Norway — reporting/audit format, not transaction-level invoicing
• EHF / Peppol addon — B2B mandatory e-invoicing proposed from 2028, not yet law

Pre-Review Checklist

• Opened this PR as a draft
• Read the CONTRIBUTING.md guide.
• Performed a self-review of my code.
• Added thorough tests with at least 90% code coverage.
• Modified or created example GOBL documents to show my changes in use, if appropriate.
• Added links to the source of the changes in tax regimes or addons, either structured or in the comments.
• Run go generate . to ensure that the Schemas and Regime data are up to date.
• Reviewed and fixed all linter warnings.
• Been obsessive with pointer nil checks to avoid panics.
• Updated the CHANGELOG.md with an overview of my changes.
• Requested a review from Copilot and fixed or dismissed (with a reason) all the feedback raised.

Only after checking off all the previous items:

• Marked this PR as ready for review and requested one from @samlown.

[0xjgv]

@samlown could you please request a review from Copilot? 🙏

[Copilot]

Pull request overview

Adds Norway (NO) as a first-class tax regime in GOBL, including VAT rate definitions, identity normalization/validation, and invoice-specific validation/scenario behavior, plus generated schema/data and example fixtures.

Changes:

• Register new NO regime and implement Norwegian VAT category/rates (incl. historical values), invoice tags/scenarios, and correction support.
• Add Norwegian identity support: organisasjonsnummer (org.Identity type ON) and tax identity normalization/validation (mod-11).
• Add tests + example documents/JSON snapshots, and update generated regime/schema data + changelog.
• (Also introduces repo-level agent/tooling files: Makefile, .claude/, agent_docs/, CLAUDE.md.)

Reviewed changes

Copilot reviewed 29 out of 35 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
regimes/regimes.go	Registers the new Norway regime via blank import.
regimes/no/no.go	Defines and registers the NO tax.RegimeDef (currency, VAT scheme, validator/normalizer, tags, scenarios, corrections).
regimes/no/tax_categories.go	VAT category + four rates with historical values and bilingual labels/sources.
regimes/no/tax_identity.go	Tax identity normalization (strip NO + MVA) and mod-11 validation.
regimes/no/identities.go	Adds org identity type ON + normalization/validation using same mod-11 logic.
regimes/no/invoices.go	Norway-specific invoice validation rules (supplier requirements, customer name, preceding refs for credit/debit).
regimes/no/scenarios.go	Adds foretaksregisteret tag + scenario note injection (and reverse-charge note).
regimes/no/*_test.go	Coverage for normalization/validation, scenarios, and invoice calc/validation behaviors.
regimes/no/README.md	Regime documentation (rates, identities, tags, scope).
examples/no/*.yaml + examples/no/out/*.json	Example invoices and expected calculated envelopes/snapshots.
data/schemas/tax/regime-code.json	Adds NO to regime-code schema enum.
data/regimes/no.json	Generated serialized regime definition for NO.
CHANGELOG.md	Notes addition of Norwegian regime in Unreleased.
Makefile	Adds dev workflow targets (build/test/generate/lint/etc.) using .claude/scripts/run_silent.sh.
.claude/settings.local.json	Adds Claude session hooks/plugins (appears local/developer-specific).
.claude/scripts/*	Adds helper scripts used by Makefile and Claude context gathering.
agent_docs/* + CLAUDE.md	Adds agent-facing documentation and repo patterns/checklists.

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[0xjgv]

@pmenendz, here is the harness to steer claude code #734

[samlown]

Solid first attempt. There are a few things I'd remove before accepting the PR in order to be more usable. Support for simplified invoices is usually a requirement.

[0xjgv]

Solid first attempt. There are a few things I'd remove before accepting the PR in order to be more usable. Support for simplified invoices is usually a requirement.

Thank you 🙏 @samlown. I’ve addressed the comments, and I really enjoyed thinking through what it takes to support a new e-invoicing regime (sources of truth, regulatory changes, company types, etc.).

[samlown]

This looks great! Thanks! Only change would be to relax the customer not-present check, then happy to merge 👍

[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.08%. Comparing base (926130f) to head (c04c2cd).

Files with missing lines	Patch %	Lines
regimes/no/tax_identity.go	91.66%	1 Missing and 2 partials ⚠️
regimes/no/invoices.go	96.22%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #728      +/-   ##
==========================================
+ Coverage   93.05%   93.08%   +0.03%     
==========================================
  Files         333      337       +4     
  Lines       17785    17945     +160     
==========================================
+ Hits        16549    16704     +155     
- Misses        870      872       +2     
- Partials      366      369       +3     

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[0xjgv]

@samlown comments addressed 👌