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

# Remote eval dev mode fails with Pydantic parameters

> [!NOTE]
>
> **Applies to:**
>
> * Plan - Any
> * Deployment - Any
> *
> * Use case - Running bt eval with --dev flag when Eval() uses Pydantic models as parameter schemas and the remote eval UI shows connection or listing errors

## Summary

**Issue:** Running `bt eval` with `--dev` fails in the Braintrust UI — the remote eval server appears to start and `/list` returns 200, but the UI cannot connect or list evals when the `Eval()` call includes a `parameters` argument using Pydantic models.

**Cause:** A bug in the `bt` CLI causes Pydantic model parameter schemas to be serialized incorrectly during remote eval dev mode, preventing the UI from loading the eval.

**Resolution:** Remove the `parameters` field from your `Eval()` call as a temporary workaround until the CLI fix is released.

## Resolution steps

### If your `Eval()` uses Pydantic models as `parameters`

#### Step 1: Remove `parameters` from `Eval()`

Comment out or delete the `parameters` argument from each affected `Eval()` call.

```python theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
# Before
Eval(
    PROJECT,
    data=init_dataset(project=PROJECT, name=DATASET),
    task=my_task,
    scores=[my_scorer],
    parameters={"thresholds": ThresholdParams},  # remove this
)

# After
Eval(
    PROJECT,
    data=init_dataset(project=PROJECT, name=DATASET),
    task=my_task,
    scores=[my_scorer],
)
```

#### Step 2: Restart the dev server

```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
bt eval your_eval.py --dev --dev-org-name "YourOrg"
```

Confirm the UI can now connect and list evals.

#### Step 3: Restore `parameters` after the CLI fix ships

The serialization bug is fixed in `bt` [v0.11.0](https://github.com/braintrustdata/bt/releases/tag/v0.11.0). Update the CLI and re-add your `parameters` argument.

```bash theme={"theme":{"light":"github-light","dark":"github-dark-dimmed"}}
bt --version  # confirm v0.11.0 or later
```


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.