> ## Documentation Index
> Fetch the complete documentation index at: https://wiki.latch.bio/llms.txt
> Use this file to discover all available pages before exploring further.

# Metadata

In order to generate the interface for your workflow on Latch, you need to specify which parameters you want to expose - and how you want to expose them - in a `latch_metadata` package.

In your workflow directory, create a folder called `latch_metadata`, and in it, add a file called `__init__.py`. The content of the file should look like this:

```python theme={null}
from dataclasses import dataclass
from typing import List

from latch.types.directory import LatchDir, LatchOutputDir
from latch.types.file import LatchFile
from latch.types.metadata.latch import LatchAuthor
from latch.types.metadata.snakemake import SnakemakeParameter
from latch.types.metadata.snakemake_v2 import SnakemakeV2Metadata


@dataclass
class Sample:
    name: str
    r1: LatchFile
    r2: LatchFile


metadata = SnakemakeV2Metadata(
    display_name="Test Workflow",
    author=LatchAuthor(),
    parameters={
        "samples": SnakemakeParameter(
            display_name="Samples",
            type=List[Sample],
            samplesheet=True,
        ),
        "results_dir": SnakemakeParameter(
            display_name="Results Dir",
            type=LatchOutputDir,
            default=LatchDir("latch://123.account/results"),
        ),
    },
)
```

The only hard requirements for this file is that it create a `SnakemakeV2Metadata` object and define an appropriate set of parameters using `SnakemakeParameter` objects. `SnakemakeParameter`s are identical to [`LatchParameter`s](/workflows/sdk/ui/latch-metadata#latchparameter), with an additional required `type` field.

Values passed through the interface will be marshalled into JSON and then provided to your workflow as an external config file. For example, in the above workflow, if we pass a single Sample called `test` with `r1` at `latch://123.account/test_r1.fastq` and `r2` at `latch://123.account/test_r2.fastq`, the resulting config file would look like

```json theme={null}
{
    "samples": [
        {
            "name": "test",
            "r1": "/ldata/123.account/test_r1.fastq",
            "r2": "/ldata/123.account/test_r2.fastq"
        }
    ],
    "results_dir": "latch://123.account/results"
}
```

These can then be accessed from within the Snakemake workflow via the `config` object, e.g. `config["samples"][0]` would get the first sample. See [encoding](./encoding) for more info.