Load Polars data to DuckDB

polars-api is a library that allows calling REST APIs from a Polars DataFrame by registering an .api namespace on expressions for synchronous and asynchronous HTTP requests. Everything needed to build a working Polars → 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 Polars 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 Polars 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 Polars 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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Polars API at a glance

These values come from the Polars API reference — the authoritative source if anything here looks out of date.

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How do I authenticate with the Polars API?

The library supports authentication via a 'bearer' token passed per-row or as a literal string using the 'bearer' argument, as well as 'api_key' headers and basic authentication via the 'auth' argument (a tuple of (user, pass)).

1. Get your credentials

Polars is a local client library, not a REST API service. If you are referring to 'Polars Cloud', obtain your API credentials from your organization's Cloud dashboard at https://docs.cloud.pola.rs/reference/auth/. For standard Polars usage in dlt pipelines, no API key is required; however, if you are using a third-party library to perform API calls from Polars (like polars-api), you would manage authentication through the specific provider's dashboard or configuration settings.

2. Add them to .dlt/secrets.toml

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[sources.polars_source]
api_key = "your_api_key_here"

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 Polars data can I load into DuckDB?

These are the Polars endpoints dlt can load into DuckDB:

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How do I load only new Polars records?

The Polars 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": "polars_api_get", "endpoint": {
    "path": "get",
    # 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 Polars pipeline look like?

A standard dlt REST API pipeline — the same code you would write by hand, loading None (Polars does not expose standard REST endpoints). from the Polars API into DuckDB:

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

@dlt.source
def polars_source(auth=dlt.secrets.value):
    config: RESTAPIConfig = {
        "client": {
            "base_url": "The library does not have a static base URL; the URL is provided as a Polars expression column for each request.",
            "auth": {"type": "bearer", "token": auth},
        },
        "resources": [
            {"name": "polars_api_get", "endpoint": {"path": "get"}},
            {"name": "polars_api_aget", "endpoint": {"path": "aget"}}
        ],
    }
    yield from rest_api_resources(config)


def load_polars_to_duckdb() -> None:
    pipeline = dlt.pipeline(
        pipeline_name="polars_pipeline",
        destination="duckdb",
        dataset_name="polars_data",
    )
    load_info = pipeline.run(polars_source())
    print(load_info)


if __name__ == "__main__":
    load_polars_to_duckdb()

Run it with python polars_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 Polars 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("polars_pipeline").dataset()
df = data.get.df()
print(df.head())

SQL:

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SELECT * FROM polars_data.get LIMIT 10;

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

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How do I deploy the Polars 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 Polars 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 Polars 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