Fortnox skillsPublished June 3, 2026
Ready-made Fortnox skills and how to build your own
A practical guide for giving an AI agent better judgement in Fortnox: which skill patterns to start with, how to structure them, and which rules keep them safe in real accounting work.
A visitor recently asked whether there are ready-made Fortnox skills, or how to build good ones. The short answer is yes. The more important point is that a good Fortnox skill is not just a list of API endpoints. It is a workflow with accounting context, error handling, and clear boundaries around changes.
Core idea
Why skills are needed on top of the API
The Fortnox API gives access to data and operations. It does not answer the whole question of how an agent should work. The agent needs to know when to choose customer invoices instead of supplier invoices, how to handle several Fortnox companies, which dates and filters matter, and when to stop instead of guessing.
That is where skills help. A skill captures the practical way to perform a recurring Fortnox job. It does not only say what can be called; it says how the agent should reason and what it should check first.
Data and operations
Fortnox API
What can be called
Way of working
Skill
Company, dates, filters and when to stop
AI agent
The agent
Knows what to check first
The Nordsynk model
Skills first, generic API discovery second
In Nordsynk, the agent uses one MCP surface. Inside it, it can search customer-facing Fortnox guidance with skills.grep, load compact metadata with skills.describe, read the full guide with skills.read, and run reviewed skill exports with skills.invoke when a workflow is sensitive or recurring.
For the long tail of the Fortnox API, codemode.grep, codemode.describe, and codemode.request are available. The idea is simple: start with a relevant skill when there is a known workflow, and fall back to API discovery when the task is new or more generic.
- 01
skills.grep
Search customer-facing Fortnox guidance.
- 02
skills.describe
Load compact metadata about the skill.
- 03
skills.read
Read the full guide.
- 04
skills.invoke
Run reviewed skill exports when a workflow is sensitive or recurring.
- 05
codemode.grep, describe, request
The long tail of the Fortnox API, when the task is new or more generic.
Ready-made Fortnox skill areas to start with
These areas show up often in real Fortnox questions, so they are good candidates for reusable skills.
Customer invoices
List, find, and summarize customer invoices — especially chasing unpaid or overdue ones, with a read on OCR, status, balance, and payment history.
Supplier invoices
Work with accounts payable, incoming invoices, OCR/interpreted rows, authorization, payment status, and overdue supplier invoices.
Vouchers and bookkeeping
Search vouchers, explain rows, look up accounts, validate debit and credit, and prepare entries without inventing accounts.
Document archive and attachments
Find uploaded files, verify file IDs, attach documents to vouchers, and handle common cases where the right ID is not the one that first looks right.
Reports and exports
Export SIE, prepare result reports, analyze revenue, accounts, and periods. Financial years and exact dates matter extra here.
Payroll
Read payroll runs, payroll periods, employees, and salary rows, but only when Fortnox permissions and product licenses actually allow it.
Example · trigger phrases
From question to skill
Phrases customers actually use
| The user says | Skill area |
|---|---|
| “Which invoices are unpaid?” | Skill areaCustomer invoices |
| “Show incoming invoices waiting for approval” | Skill areaSupplier invoices |
| “Explain the rows in voucher 214” | Skill areaVouchers and bookkeeping |
| “Export SIE for last year” | Skill areaReports and exports |
| “Prepare the result report for March” | Skill areaReports and exports |
The anatomy of a good Fortnox skill
A skill does not need to be long. It needs to be clear where the agent would otherwise make mistakes.
1. Trigger in the user's language
Use triggers customers actually say: unpaid invoices, incoming invoices, approval, SIE, vouchers, result report. API names can be included, but they should not be the only entry point.
2. Company context first
If the user has several Fortnox companies, the skill should tell the agent to select or ask for the right company before reading or writing.
3. Describe schema before uncertain calls
When filters, path parameters, or request bodies are uncertain, the agent should inspect the surface first. This reduces invalid filters, wrong years, and wrong field names.
4. Changes are separate decisions
Create, update, bookkeep, email, approve, and delete are changes. In Nordsynk, changes open a browser approval preview by default; a company can enable auto-approve. Fortnox permissions and Nordsynk access policies always apply.
5. Error handling that stops guessing
A good skill explains what the agent should do for common Fortnox errors. Sometimes the correct behavior is to stop, report the blocker, and ask the customer to fix permissions, matching, or period setup.
Example · sample error
Error handling · Payroll
I'm stopping here: Fortnox reports that permission or the product license for payroll is missing for the connected user. Ask an administrator to adjust the permission and I'll read the run right away. I won't guess any amounts.
Five rules for reliable Fortnox skills
Keep each skill narrow
A skill for supplier invoices and authorization will be better than a generic skill for the whole finance department. Narrow skills produce clearer triggers and better error handling.
Codify the exceptions
The easy-to-miss details should live in the skill: the right file ID, the right SIE parameter, the right financial year, or that OCR rows are not always finished supplier invoices.
Fetch context once
If many voucher rows need account names, fetch the chart of accounts once and join locally instead of making one request per account.
Be explicit about uncertainty
If Fortnox permissions, product licensing, or period setup makes the answer uncertain, the agent should say so. Accounting work benefits from precision, not confident guesses.
Let reads and changes have different rhythm
Reads can be fast and iterative. By default, Nordsynk shows the target company, action, key details, and consequence in a browser approval preview. Company-scoped auto-approve can be enabled; Fortnox permissions and Nordsynk access policies always apply.
Example · sample invoice
Preview · Fortnox
Book supplier invoice 1042, Telia, 1 249 kr
Requested via Claude · Acme AB
| Account | In Fortnox now | After approval |
|---|---|---|
| 6212 Mobile phone | In Fortnox now— | After approval999.20 debit |
| 2641 Input VAT | In Fortnox now— | After approval249.80 debit |
| 2440 Accounts payable | In Fortnox now— | After approval1 249.00 credit |
Nothing is written to Fortnox until you approve, unless the company has enabled auto-approve.
A simple template
This compact structure works for most Fortnox skills.
---
name: fortnox-supplier-invoices
description: Use when the user asks about supplier invoices, incoming invoices, OCR, attest, payment approval, or overdue accounts payable.
---
# Fortnox Supplier Invoices
## Overview
Use this skill for supplier invoice questions and workflows.
## Workflow
1. Resolve the Fortnox company if ambiguous.
2. Search the relevant invoice, OCR, inbox, authorization, or payment surface.
3. Describe the endpoint before uncertain filters or writes.
4. Read with the narrowest useful filters.
5. For Nordsynk writes, summarize the operation and follow the company's configured approval mode: browser preview by default, or company-scoped auto-approve when enabled. Fortnox permissions and Nordsynk access policies always apply.
## Rules
- Do not assume an incoming OCR row already has a supplier invoice number.
- Do not invent suppliers, accounts, dates, or authorizers.
- Stop on deterministic validation or permission errors and report the blocker.
Start narrow, let judgment grow from there
Good Fortnox skills make the agent more accounting-aware, not just more technical: it learns the language the chart of accounts actually uses, where the checkpoints sit, and when to stop and ask instead of guessing. Start with a narrow workflow, write down what an experienced accountant would verify, and let API discovery be the tool that does the work — not the substitute for judgement.