# Experiments

:::callout{intent="note"}
In Opik 2.0, experiments are project-scoped. Make sure to specify a `projectName` when running experiments so they are associated with the correct project.
:::

Experiments in Opik allow you to link traces (execution data) with dataset items to create a foundation for evaluation and comparison. Experiments let you track, analyze, and compare the performance of your LLM applications across different versions, models, or configurations.

## What are Experiments?

An experiment in Opik connects traces (records of LLM executions) with dataset items, creating a linkage that enables structured evaluation and analysis. This connection allows you to:

- Compare different LLM implementations against the same dataset
- Evaluate model performance with various metrics
- Track improvements or regressions over time
- Analyze feedback scores across different versions

## Creating and Managing Experiments

The TypeScript SDK provides several methods to create and manage experiments through the `OpikClient` class.

### Getting Experiments

```typescript
// Get all experiments with a specific name
const experiments = await opik.getExperimentsByName("my-experiment");

// Get a single experiment by name (first match if multiple exist)
const experiment = await opik.getExperiment("my-experiment");

// Get all experiments associated with a dataset
const datasetExperiments = await opik.getDatasetExperiments("my-dataset", 100); // Optional maxResults parameter (default: 100)
```

### Updating an Experiment

```typescript
// Update experiment name
await opik.updateExperiment("experiment-id", {
  name: "Updated Experiment Name"
});

// Update experiment configuration
await opik.updateExperiment("experiment-id", {
  experimentConfig: {
    model: "gpt-5",
    temperature: 0.7,
    promptTemplate: "Answer the following question: {question}"
  }
});

// Update both name and configuration
await opik.updateExperiment("experiment-id", {
  name: "Updated Experiment Name",
  experimentConfig: {
    model: "gpt-5",
    temperature: 0.7
  }
});
```

### Deleting an Experiment

```typescript
// Delete an experiment by ID
await opik.deleteExperiment("experiment-id");
```

## Working with Experiment Items

Experiment items are the core components that link dataset items with traces. These connections enable you to analyze how your LLM application performs on specific inputs.

### Creating Experiment Items

```typescript
import { ExperimentItemReferences } from "opik";

// Get an existing experiment
const experiment = await opik.getExperiment("my-experiment");

// Create references between dataset items and traces
const experimentItems = [
  new ExperimentItemReferences({
    datasetItemId: "dataset-item-1",
    traceId: "trace-id-1",
  }),
  new ExperimentItemReferences({
    datasetItemId: "dataset-item-2",
    traceId: "trace-id-2",
  }),
];

// Insert the experiment items
await experiment.insert(experimentItems);
```

### Retrieving Experiment Items

```typescript
// Get all items in an experiment
const allItems = await experiment.getItems();

// Get a limited number of items
const limitedItems = await experiment.getItems({ maxResults: 50 });

// Get items with truncated data (improves performance for large datasets)
const truncatedItems = await experiment.getItems({ truncate: true });
```

## Experiment URL

Get the URL to view the experiment in the Opik web interface:

```typescript
const url = await experiment.getUrl();
console.log(`View experiment at: ${url}`);
```

## Data Structures

### Experiment

Represents an experiment in Opik that connects traces with dataset items:

```typescript
class Experiment {
  readonly id: string; // Unique identifier of the experiment
  readonly name?: string; // Optional name of the experiment
  readonly datasetName: string; // Name of the dataset associated with the experiment

  // Creates new experiment items by linking traces with dataset items
  insert(experimentItemReferences: ExperimentItemReferences[]): Promise<void>;

  // Retrieves experiment items with options for pagination and data truncation
  getItems(options?: {
    maxResults?: number; // Maximum number of items to retrieve
    truncate?: boolean; // Whether to truncate large data fields
  }): Promise<ExperimentItemContent[]>;

  // Gets the URL to view the experiment in the Opik web interface
  getUrl(): Promise<string>;
}
```

### ExperimentItemReferences

References connecting a dataset item to a trace:

```typescript
interface ExperimentItemReferences {
  readonly datasetItemId: string; // ID of the dataset item
  readonly traceId: string; // ID of the trace
}
```

### ExperimentItemContent

Content of an experiment item including evaluation data and feedback scores:

```typescript
interface ExperimentItemContent {
  readonly id?: string; // Experiment item ID
  readonly datasetItemId: string; // Dataset item ID
  readonly traceId: string; // Trace ID
  readonly datasetItemData?: JsonListStringCompare; // Dataset item data
  readonly evaluationTaskOutput?: JsonListStringCompare; // Evaluation task output
  readonly feedbackScores: FeedbackScore[]; // Feedback scores for the item
}
```

### FeedbackScore

Represents a feedback score for an experiment item:

```typescript
interface FeedbackScore {
  categoryName: string; // Category of the feedback
  name: string; // Name of the feedback metric
  reason?: string; // Optional reason for the score
  value: number; // Score value
  source: string; // Source of the feedback
}
```

## Related pages

- [Evaluation](./typescript-sdk-evaluation-overview.md)
- [Quick Start](./typescript-sdk-evaluation-quick-start.md)
- [Datasets](./typescript-sdk-evaluation-datasets.md)
- [Evaluate Function](./typescript-sdk-evaluation-evaluate-function.md)
- [evaluatePrompt Function](./typescript-sdk-evaluation-evaluate-prompt-function.md)
- [Models](./typescript-sdk-evaluation-models.md)
- [Evaluation Metrics](./typescript-sdk-evaluation-metrics.md)
- [Test Suites](./typescript-sdk-evaluation-test-suites.md)

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