Load Fortnox data to DuckDB

Fortnox is an accounting and business management platform that provides a REST API for accessing financial data, customers, invoices, and other business resources. Everything needed to build a working Fortnox → DuckDB pipeline is on this page: the API's base URL, authentication, endpoints, pagination and incremental field — plus a prompt that hands the whole job to your coding agent.

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Build your Fortnox to DuckDB pipeline

Paste this prompt into Claude, Codex, or Cursor. The agent does the rest.

PromptCopy prompt
Run uvx dlthub-init@latest to build a pipeline from Fortnox to DuckDB and run it on dltHub

That scaffolds a dltHub workspace and installs the dltHub AI harness — the project rules, the secrets-management skill, and the dlt MCP server your agent needs to work safely. From there it reads the Fortnox API, proposes the endpoints to load, then writes, runs and validates the pipeline while you review rather than type. Credentials are inspected through MCP tools, so your agent never reads secrets.toml itself. How the LLM-native workflow works →

Prefer to write it yourself? Every fact the agent uses is below.

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Fortnox API at a glance

These values come from the Fortnox API reference — the authoritative source if anything here looks out of date.

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How do I authenticate with the Fortnox API?

Authentication is performed by sending an Authorization header with the format 'Bearer {Access-Token}'. The header 'Accept: application/json' is also typically required to ensure JSON response format.

1. Get your credentials

1. Log in to your Fortnox account and navigate to the Developer Portal (Menu -> Developer Portal).
2. Click 'Create new integration' to define your application.
3. Provide a name, select the required scopes, and define a redirect URI.
4. Save the integration to generate your Client ID and Client Secret.
5. Direct users to the Fortnox authorization URL (https://apps.fortnox.se/oauth-v1/auth) using your Client ID and redirect URI to obtain an authorization code.
6. Exchange the authorization code at the token endpoint (https://apps.fortnox.se/oauth-v1/token) using your Client ID and Client Secret to receive your initial access token and refresh token.

2. Add them to .dlt/secrets.toml

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[sources.fortnox_source]
client_id = "your_client_id"
client_secret = "your_client_secret"
access_token = "your_access_token"
refresh_token = "your_refresh_token"

dlt reads this file automatically at runtime. With the harness, the setup-secrets skill prompts you for the values and never handles the raw credential in chat. For production, see setting up credentials with dlt.

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What Fortnox data can I load into DuckDB?

These are the Fortnox endpoints dlt can load into DuckDB:

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How do I load only new Fortnox records?

The Fortnox API reference does not document a timestamp or sequence field for these endpoints, so there is nothing to advertise here as verified. Pick a field from the endpoints table above that increases with every write, then set it as the cursor_path.

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{"name": "customers", "endpoint": {
    "path": "3/customers",
    # Replace with a field that increases on every write.
    "incremental": {"cursor_path": "REPLACE_ME", "initial_value": "2024-01-01T00:00:00Z"},
}}

On the first run dlt loads everything from initial_value; on every run after that it requests only what changed and appends with write_disposition="merge" if you set a primary key. See incremental loading.

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What does the generated Fortnox pipeline look like?

A standard dlt REST API pipeline — the same code you would write by hand, loading /oauth-v1/token and /3/companyinformation from the Fortnox API into DuckDB:

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import dlt
from dlt.sources.rest_api import RESTAPIConfig, rest_api_resources

@dlt.source
def fortnox_source(access_token=dlt.secrets.value):
    config: RESTAPIConfig = {
        "client": {
            "base_url": "https://api.fortnox.se/3",
            "auth": {"type": "bearer", "token": access_token},
        },
        "resources": [
            {"name": "customers", "endpoint": {"path": "3/customers", "data_selector": "Customers"}},
            {"name": "invoices", "endpoint": {"path": "3/invoices", "data_selector": "Invoices"}}
        ],
    }
    yield from rest_api_resources(config)


def load_fortnox_to_duckdb() -> None:
    pipeline = dlt.pipeline(
        pipeline_name="fortnox_pipeline",
        destination="duckdb",
        dataset_name="fortnox_data",
    )
    load_info = pipeline.run(fortnox_source())
    print(load_info)


if __name__ == "__main__":
    load_fortnox_to_duckdb()

Run it with python fortnox_pipeline.py. The agent iterates on this until it loads cleanly — you review and approve, rather than write it from scratch.

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How do I query Fortnox data in DuckDB?

dlt creates one table per resource. Query the loaded data with Python or SQL — or ask your agent to, through the MCP server's execute_sql_query tool.

Python (pandas DataFrame):

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import dlt

data = dlt.pipeline("fortnox_pipeline").dataset()
df = data.invoices.df()
print(df.head())

SQL:

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SELECT * FROM fortnox_data.invoices LIMIT 10;

See querying your data with dataset and exploring it in marimo notebooks.

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How do I deploy the Fortnox to DuckDB pipeline in production?

The pipeline runs locally, which is ideal for prototyping and one-off analysis. When you need it on a schedule, monitored on every load, and shared with your team, deploy the same dlt code on the dltHub platform — no infrastructure to maintain. The prompt above already ends with "run it on dltHub", so your agent can take it there directly.

• Deploy & schedule — run the pipeline as a managed job with automatic retries.
• Monitor — observable job queues, alerting, and load metrics for every run.
• Transform — promote raw Fortnox loads into governed, documented models.
• Visualize & share — explore data in notebooks and publish live dashboards instead of static screenshots.

Book a demo →

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What other destinations can I load Fortnox data to?

dlt loads into any of these — only the destination argument changes:

Set dlt.pipeline(destination="snowflake") and add credentials in .dlt/secrets.toml. On the dltHub platform the same pipeline runs against a managed Iceberg lakehouse. See the full destinations list.

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Next steps

• Ready for production? Book a demo of the dltHub platform →
• dlt LLM-native workflow docs
• REST API source reference
• Join the dlt community on Slack