Fortnox Python API Docs | dltHub

Fortnox is a cloud‑based accounting and ERP platform offering a REST API for financial data. The REST API base URL is https://api.fortnox.se/3/ and All requests require an Access‑Token and Client‑Secret header for authentication..

dlt is an open-source Python library that handles authentication, pagination, and schema evolution automatically. dlthub provides AI context files that enable code assistants to generate production-ready pipelines. Install with uv pip install "dlt[workspace]" and start loading Fortnox data in under 10 minutes.

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What data can I load from Fortnox?

Here are some of the endpoints you can load from Fortnox:

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How do I authenticate with the Fortnox API?

Include the Access‑Token header (Bearer JWT, 1 hour expiry) and the Client‑Secret header (provided by your Fortnox app) on every request.

1. Get your credentials

1. Log in to the Fortnox developer portal.
2. Create a new application to receive a Client ID and Client Secret.
3. Set a redirect URI and required scopes.
4. Direct a user to the authorization endpoint to obtain an authorization code.
5. Call the token endpoint (https://apps.fortnox.se/oauth-v1/token) with the code, client_id and client_secret to receive an access token (JWT, 1 hour) and a refresh token (45 days).
6. Store the tokens securely for use in API calls.

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 automatically at runtime — never hardcode tokens in your pipeline script. For production environments, see setting up credentials with dlt for environment variable and vault-based options.

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How do I set up and run the pipeline?

Set up a virtual environment and install dlt:

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uv venv && source .venv/bin/activate
uv pip install "dlt[workspace]"

1. Install the dlt AI Workbench:

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dlt ai init --agent <your-agent> # <agent>: claude | cursor | codex

This installs project rules, a secrets management skill, appropriate ignore files, and configures the dlt MCP server for your agent. Learn more →

2. Install the rest-api-pipeline toolkit:

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dlt ai toolkit rest-api-pipeline install

This loads the skills and context about dlt the agent uses to build the pipeline iteratively, efficiently, and safely. The agent uses MCP tools to inspect credentials — it never needs to read your secrets.toml directly. Learn more →

3. Start LLM-assisted coding:

Use /find-source to load data from the Fortnox API into DuckDB.

The rest-api-pipeline toolkit takes over from here — it reads relevant API documentation, presents you with options for which endpoints to load, and follows a structured workflow to scaffold, debug, and validate the pipeline step by step.

4. Run the pipeline:

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python fortnox_pipeline.py

If everything is configured correctly, you'll see output like this:

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Pipeline fortnox_pipeline load step completed in 0.26 seconds
1 load package(s) were loaded to destination duckdb and into dataset fortnox_data
The duckdb destination used duckdb:/fortnox.duckdb location to store data
Load package 1749667187.541553 is LOADED and contains no failed jobs

Inspect your pipeline and data:

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dlt pipeline fortnox_pipeline show

This opens the Pipeline Dashboard where you can verify pipeline state, load metrics, schema (tables, columns, types), and query the loaded data directly.

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Python pipeline example

This example loads customers and invoices from the Fortnox API into DuckDB. It mirrors the endpoint and data selector configuration from the table above:

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

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


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

To add more endpoints, append entries from the resource table to the "resources" list using the same name, path, and data_selector pattern.

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How do I query the loaded data?

Once the pipeline runs, dlt creates one table per resource. You can query with Python or SQL.

Python (pandas DataFrame):

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import dlt

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

SQL (DuckDB example):

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SELECT * FROM fortnox_data.customers LIMIT 10;

In a marimo or Jupyter notebook:

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import dlt

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

See how to explore your data in marimo Notebooks and how to query your data in Python with dataset.

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What destinations can I load Fortnox data to?

dlt supports loading into any of these destinations — only the destination parameter changes:

Change the destination in dlt.pipeline(destination="snowflake") and add credentials in .dlt/secrets.toml. See the full destinations list.

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Troubleshooting

Authentication failures

• Return code 401 with an error payload indicating an invalid or expired Access‑Token. Refresh the token using the refresh token endpoint.

Rate limits

• The API allows 25 requests per 5 seconds (≈300 per minute). Exceeding this returns 429 Too Many Requests. Implement exponential back‑off before retrying.

Pagination

• List endpoints support pagination via page and limit query parameters. The response includes @CurrentPage, @TotalPages, and @TotalResources fields to navigate pages.

Ensure that the API key is valid to avoid 401 Unauthorized errors. Also, verify endpoint paths and parameters to avoid 404 Not Found errors.

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Next steps

Continue your data engineering journey with the other toolkits of the dltHub AI Workbench:

• data-exploration — Build custom notebooks, charts, and dashboards for deeper analysis with marimo notebooks.
• dlthub-runtime — Deploy, schedule, and monitor your pipeline in production.

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dlt ai toolkit data-exploration install
dlt ai toolkit dlthub-runtime install

• How to deploy a pipeline
• How to explore your data in marimo Notebooks
• How to query your data in Python with dataset
• Join the dlt community on Slack