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Beagle’s plugin system allows you to create custom log types for any data you want to track. This guide walks through creating a custom plugin using a real example from the Beagle repository.

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Plugin Architecture

Every Beagle plugin consists of two parts:
  1. Log Class: Extends BeagleLog to store your custom data
  2. Plugin Class: Extends BeagleLogPlugin to handle and display the log

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Step-by-Step Guide

We’ll create an analytics plugin that tracks events and parameters, using the actual implementation from the Beagle example app.
1

Create the Log Class

First, create a class that extends BeagleLog to hold your custom data:
import { BeagleLog } from 'react-native-beagle';

export class AnalyticsLog extends BeagleLog {
  event: string;
  params: Record<string, any>;

  constructor(event: string, params: Record<string, any>) {
    super(`Log ${event}`, 'info');
    this.event = event;
    this.params = params;
  }
}
The constructor calls super() with:
  • A message that appears in the log list
  • A log level ('info', 'error', 'warning', etc.)
2

Extend BeagleLogPlugin

Create a plugin class that extends BeagleLogPlugin:
import {
  BeagleLogPlugin,
  type BeagleLog,
  type DetailContent,
} from 'react-native-beagle';
import { AnalyticsLog } from './types';

export class AnalyticsLogPlugin extends BeagleLogPlugin<AnalyticsLog> {
  name: string = 'Analytics';

  canHandle(log: BeagleLog): log is AnalyticsLog {
    return log instanceof AnalyticsLog;
  }

  provideDetailContent(log: AnalyticsLog): DetailContent {
    return {
      key: 'analytics',
      kind: 'list',
      children: [
        {
          kind: 'label',
          label: 'Event',
          value: log.event,
        },
        { kind: 'text', text: 'Parameters', variant: 'body', bold: true },
        {
          kind: 'json',
          data: log.params,
        },
      ],
    };
  }
}
3

Implement canHandle

The canHandle method determines if this plugin can handle a given log:
canHandle(log: BeagleLog): log is AnalyticsLog {
  return log instanceof AnalyticsLog;
}
This uses TypeScript’s type guard to check if the log is an instance of your custom log class.
4

Implement provideDetailContent

The provideDetailContent method defines how your log appears in the detail view:
provideDetailContent(log: AnalyticsLog): DetailContent {
  return {
    key: 'analytics',
    kind: 'list',
    children: [
      {
        kind: 'label',
        label: 'Event',
        value: log.event,
      },
      { kind: 'text', text: 'Parameters', variant: 'body', bold: true },
      {
        kind: 'json',
        data: log.params,
      },
    ],
  };
}
This creates a list view with:
  • A label showing the event name
  • A bold text header for “Parameters”
  • A JSON tree view of the event parameters
5

Register the Plugin

Register your plugin with Beagle before logging any data:
import { Beagle } from 'react-native-beagle';
import { AnalyticsLogPlugin } from './plugins/Analytics/AnalyticsLogPlugin';

// Register the plugin (do this once, typically in your app's entry point)
Beagle.registerPlugin(new AnalyticsLogPlugin());
6

Use Your Custom Log

Now you can log analytics events throughout your app:
import { Beagle } from 'react-native-beagle';
import { AnalyticsLog } from './plugins/Analytics/types';

// Log an analytics event
Beagle.log(
  new AnalyticsLog('button_clicked', {
    screen: 'home',
    button_id: 'checkout',
    user_id: '12345',
  })
);

// Log another event
Beagle.log(
  new AnalyticsLog('purchase_completed', {
    product_id: 'ABC123',
    price: 29.99,
    currency: 'USD',
  })
);
You can also customize how logs appear in the list view by implementing provideCardFooter: 
import type { BoxContent, Content } from 'react-native-beagle';

export class AnalyticsLogPlugin extends BeagleLogPlugin<AnalyticsLog> {
  // ... other methods ...

  provideCardFooter(log: AnalyticsLog): Content | BoxContent | null {
    return {
      kind: 'text',
      text: `${Object.keys(log.params).length} parameters`,
      variant: 'caption',
    };
  }
}
This displays a parameter count at the bottom of each analytics log card.

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Complete Working Example

Here’s the complete implementation with both files: 
import { BeagleLog } from 'react-native-beagle';

export class AnalyticsLog extends BeagleLog {
  event: string;
  params: Record<string, any>;

  constructor(event: string, params: Record<string, any>) {
    super(`Log ${event}`, 'info');
    this.event = event;
    this.params = params;
  }
}

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Plugin Best Practices

Always register your plugins before logging any data. Unregistered log types will fall back to basic rendering without custom detail views.
Use the name property to identify your plugin in the Beagle UI. This appears in filters and export options.

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Tips for Building Plugins

  1. Keep log messages concise: The message appears in the list view, so make it scannable
  2. Use appropriate log levels: This helps with visual filtering in the inspector
  3. Structure detail content logically: Group related information using sections
  4. Leverage content types: Use json, label, section, and text to create rich views
  5. Add card footers for key metrics: Show important data without opening the detail view

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Advanced: Custom Export

You can customize how logs are exported by overriding exportToJSON: 
export class AnalyticsLogPlugin extends BeagleLogPlugin<AnalyticsLog> {
  // ... other methods ...

  exportToJSON(log: AnalyticsLog): string {
    return JSON.stringify({
      timestamp: log.time.toISOString(),
      event: log.event,
      parameters: log.params,
    }, null, 2);
  }
}
This formats the exported data in a custom structure optimized for your analytics pipeline.

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