Modifiers

Overview

Modifiers are powerful hooks that allow you to intercept and transform tool operations at different stages. You can use modifiers to customize request parameters, transform responses, add logging, implement custom caching, and more.

Types of Modifiers

Composio supports three types of modifiers:

Schema Modifiers - Transform tool schemas before they’re exposed
Before Execute Modifiers - Modify parameters before tool execution
After Execute Modifiers - Transform responses after tool execution

Schema Modifiers

Schema modifiers allow you to customize tool metadata, parameters, and descriptions before tools are used.

Basic Schema Modification

import { Composio } from 'composio-core';

const composio = new Composio({
  apiKey: process.env.COMPOSIO_API_KEY
});

const tools = await composio.tools.getRawComposioTools(
  {
    toolkits: ['github']
  },
  {
    modifySchema: ({ toolSlug, toolkitSlug, schema }) => {
      // Customize the schema
      return {
        ...schema,
        name: `Custom ${schema.name}`,
        description: `Enhanced: ${schema.description}`,
        tags: [...(schema.tags || []), 'customized']
      };
    }
  }
);

Adding Custom Metadata

const tools = await composio.tools.getRawComposioTools(
  { tools: ['GITHUB_GET_REPOS'] },
  {
    modifySchema: ({ schema, toolSlug }) => {
      return {
        ...schema,
        // Add custom metadata
        metadata: {
          organization: 'acme-corp',
          department: 'engineering',
          customId: `tool_${toolSlug.toLowerCase()}`
        },
        // Enhance descriptions for better AI understanding
        description: `${schema.description}. This tool is maintained by the engineering team.`,
        // Add usage examples
        examples: [
          {
            description: 'Get public repositories',
            arguments: { owner: 'composio', type: 'public' }
          }
        ]
      };
    }
  }
);

Modifying Input Parameters

const tools = await composio.tools.getRawComposioTools(
  { tools: ['HACKERNEWS_GET_USER'] },
  {
    modifySchema: ({ schema }) => {
      return {
        ...schema,
        inputParameters: {
          ...schema.inputParameters,
          properties: {
            ...schema.inputParameters.properties,
            userId: {
              ...schema.inputParameters.properties?.userId,
              description: 'HackerNews username (2-15 characters)',
              minLength: 2,
              maxLength: 15,
              pattern: '^[a-zA-Z0-9_-]+$'
            },
            // Add new optional parameters
            includeSubmissions: {
              type: 'boolean',
              description: 'Include user submissions in response',
              default: false
            }
          },
          required: [...(schema.inputParameters.required || [])]
        }
      };
    }
  }
);

Tool-Specific Modifications

const tools = await composio.tools.getRawComposioTools(
  { toolkits: ['github', 'slack'] },
  {
    modifySchema: ({ schema, toolSlug, toolkitSlug }) => {
      // Apply toolkit-specific modifications
      if (toolkitSlug === 'github') {
        return {
          ...schema,
          name: `GitHub: ${schema.name}`,
          tags: [...(schema.tags || []), 'version-control', 'github']
        };
      }
      
      if (toolkitSlug === 'slack') {
        return {
          ...schema,
          name: `Slack: ${schema.name}`,
          tags: [...(schema.tags || []), 'communication', 'slack']
        };
      }
      
      // Apply tool-specific modifications
      if (toolSlug === 'GITHUB_CREATE_ISSUE') {
        return {
          ...schema,
          description: `${schema.description} - Automatically adds organization labels`,
          metadata: {
            autoLabels: ['bug', 'internal']
          }
        };
      }
      
      return schema;
    }
  }
);

Before Execute Modifiers

Before execute modifiers intercept and modify parameters before a tool is executed.

Basic Parameter Modification

const result = await composio.tools.execute(
  'GITHUB_GET_REPOS',
  {
    userId: 'user_123',
    version: '20250909_00',
    arguments: {
      owner: 'composio'
    }
  },
  {
    beforeExecute: async ({ toolSlug, toolkitSlug, params }) => {
      console.log(`Executing ${toolSlug} from ${toolkitSlug}`);
      
      // Add tracking metadata
      return {
        ...params,
        arguments: {
          ...params.arguments,
          per_page: 100 // Always fetch max results
        }
      };
    }
  }
);

Adding Authentication Headers

const beforeExecute = async ({ params, toolSlug }) => {
  return {
    ...params,
    customAuthParams: {
      ...params.customAuthParams,
      headers: {
        ...params.customAuthParams?.headers,
        'X-Request-ID': generateRequestId(),
        'X-Tool-Slug': toolSlug,
        'X-Timestamp': new Date().toISOString()
      }
    }
  };
};

const result = await composio.tools.execute(
  'GITHUB_GET_REPOS',
  { userId: 'user_123', version: '20250909_00', arguments: { owner: 'composio' } },
  { beforeExecute }
);

Conditional Parameter Transformation

const beforeExecute = async ({ toolSlug, params }) => {
  switch (toolSlug) {
    case 'GITHUB_SEARCH_REPOS':
      // Enhance search with additional filters
      return {
        ...params,
        arguments: {
          ...params.arguments,
          q: `${params.arguments.query} language:typescript stars:>100`,
          sort: 'stars',
          order: 'desc'
        }
      };
    
    case 'SLACK_SEND_MESSAGE':
      // Add default channel if not specified
      return {
        ...params,
        arguments: {
          channel: '#general',
          ...params.arguments
        }
      };
    
    default:
      return params;
  }
};

Input Validation

const beforeExecute = async ({ toolSlug, params }) => {
  // Validate and sanitize inputs
  if (toolSlug === 'GITHUB_CREATE_ISSUE') {
    const { title, body } = params.arguments;
    
    if (!title || title.trim().length === 0) {
      throw new Error('Issue title cannot be empty');
    }
    
    if (title.length > 200) {
      throw new Error('Issue title too long (max 200 characters)');
    }
    
    return {
      ...params,
      arguments: {
        ...params.arguments,
        title: title.trim(),
        body: body?.trim() || 'No description provided'
      }
    };
  }
  
  return params;
};

After Execute Modifiers

After execute modifiers transform responses after a tool has executed.

Basic Response Transformation

const result = await composio.tools.execute(
  'GITHUB_LIST_REPOS',
  {
    userId: 'user_123',
    version: '20250909_00',
    arguments: { owner: 'composio' }
  },
  {
    afterExecute: async ({ result, toolSlug }) => {
      if (!result.successful) {
        return result;
      }
      
      // Transform response data
      return {
        ...result,
        data: {
          repositories: result.data.items.map(repo => ({
            name: repo.name,
            url: repo.html_url,
            stars: repo.stargazers_count,
            language: repo.language
          })),
          count: result.data.items.length,
          executedAt: new Date().toISOString()
        }
      };
    }
  }
);

Error Enhancement

const afterExecute = async ({ result, toolSlug, toolkitSlug }) => {
  if (!result.successful) {
    // Enhance error with additional context
    return {
      ...result,
      error: {
        ...result.error,
        toolSlug,
        toolkitSlug,
        timestamp: new Date().toISOString(),
        retryable: isRetryableError(result.error),
        suggestedAction: getSuggestedAction(result.error)
      }
    };
  }
  
  return result;
};

function isRetryableError(error) {
  const retryableCodes = ['RATE_LIMIT', 'TIMEOUT', 'SERVICE_UNAVAILABLE'];
  return retryableCodes.includes(error?.code);
}

function getSuggestedAction(error) {
  switch (error?.code) {
    case 'RATE_LIMIT':
      return 'Wait before retrying or use a different account';
    case 'AUTHENTICATION_FAILED':
      return 'Refresh the connected account credentials';
    case 'TIMEOUT':
      return 'Retry the operation or reduce the request size';
    default:
      return 'Check the error details and retry if appropriate';
  }
}

Response Filtering and Enrichment

const afterExecute = async ({ result, toolSlug }) => {
  if (!result.successful || toolSlug !== 'GITHUB_LIST_REPOS') {
    return result;
  }
  
  const repos = result.data.items;
  
  // Filter and enrich repositories
  const enrichedRepos = repos
    .filter(repo => !repo.archived && !repo.disabled)
    .map(repo => ({
      ...repo,
      // Add computed fields
      isPopular: repo.stargazers_count > 1000,
      lastUpdated: new Date(repo.updated_at).toLocaleDateString(),
      mainBranch: repo.default_branch || 'main',
      // Add health score
      healthScore: calculateRepoHealth(repo)
    }));
  
  return {
    ...result,
    data: {
      repositories: enrichedRepos,
      stats: {
        total: enrichedRepos.length,
        popular: enrichedRepos.filter(r => r.isPopular).length,
        languages: [...new Set(enrichedRepos.map(r => r.language))]
      }
    }
  };
};

function calculateRepoHealth(repo) {
  let score = 0;
  if (repo.has_issues) score += 20;
  if (repo.has_wiki) score += 20;
  if (repo.description) score += 20;
  if (repo.license) score += 20;
  if (repo.topics?.length > 0) score += 20;
  return score;
}

Logging and Monitoring

const afterExecute = async ({ result, toolSlug, toolkitSlug }) => {
  // Log execution metrics
  const metrics = {
    toolSlug,
    toolkitSlug,
    successful: result.successful,
    timestamp: new Date().toISOString(),
    logId: result.logId
  };
  
  if (result.successful) {
    console.log('[Tool Success]', metrics);
    // Send to analytics
    await analytics.track('tool_execution_success', metrics);
  } else {
    console.error('[Tool Error]', { ...metrics, error: result.error });
    // Send to error tracking
    await errorTracking.captureError(result.error, metrics);
  }
  
  return result;
};

Combining Modifiers

You can use multiple modifiers together for powerful customization:

const tools = await composio.tools.get(
  'user_123',
  { toolkits: ['github'] },
  {
    // Schema modification
    modifySchema: ({ schema, toolSlug }) => ({
      ...schema,
      name: `Custom ${schema.name}`,
      metadata: { customId: toolSlug }
    }),
    
    // Before execution
    beforeExecute: async ({ params, toolSlug }) => {
      console.log(`Executing: ${toolSlug}`);
      return {
        ...params,
        allowTracing: true // Enable tracing for all tools
      };
    },
    
    // After execution
    afterExecute: async ({ result, toolSlug }) => {
      console.log(`Completed: ${toolSlug}`);
      return result;
    }
  }
);

Tool Router Meta Tool Modifiers

For tool router sessions, use session-specific modifiers:

const sessionTools = await composio.toolRouter.getTools(sessionId, {
  modifySchema: ({ schema, toolSlug }) => ({
    ...schema,
    description: `[Session Tool] ${schema.description}`
  }),
  
  beforeExecute: async ({ toolSlug, sessionId, params }) => {
    console.log(`Executing ${toolSlug} in session ${sessionId}`);
    return {
      ...params,
      sessionMetadata: {
        sessionId,
        timestamp: Date.now()
      }
    };
  },
  
  afterExecute: async ({ result, toolSlug, sessionId }) => {
    console.log(`Completed ${toolSlug} in session ${sessionId}`);
    return {
      ...result,
      sessionInfo: {
        sessionId,
        completedAt: new Date().toISOString()
      }
    };
  }
});

Best Practices

Keep Modifiers Pure

Avoid side effects in modifiers. Return new objects instead of mutating existing ones.

Handle Errors Gracefully

Wrap modifier logic in try-catch blocks to prevent breaking tool execution.

Use Type Safety

Leverage TypeScript types to ensure modifier functions match expected signatures.

Performance Matters

Keep modifiers lightweight. Heavy operations should be async and properly awaited.

Common Use Cases

Caching Responses

const cache = new Map();

const cacheModifiers = {
  beforeExecute: async ({ toolSlug, params }) => {
    const cacheKey = `${toolSlug}:${JSON.stringify(params.arguments)}`;
    if (cache.has(cacheKey)) {
      console.log('Cache hit:', cacheKey);
    }
    return params;
  },
  
  afterExecute: async ({ result, toolSlug, params }) => {
    if (result.successful) {
      const cacheKey = `${toolSlug}:${JSON.stringify(params.arguments)}`;
      cache.set(cacheKey, result.data);
    }
    return result;
  }
};

Rate Limiting

const rateLimiter = new Map();

const rateLimitModifier = async ({ toolSlug, params }) => {
  const now = Date.now();
  const lastCall = rateLimiter.get(toolSlug) || 0;
  const minInterval = 1000; // 1 second between calls
  
  if (now - lastCall < minInterval) {
    const waitTime = minInterval - (now - lastCall);
    await new Promise(resolve => setTimeout(resolve, waitTime));
  }
  
  rateLimiter.set(toolSlug, Date.now());
  return params;
};

Request/Response Logging

const loggingModifiers = {
  beforeExecute: async ({ toolSlug, params }) => {
    console.log(`[${new Date().toISOString()}] Executing ${toolSlug}`, {
      arguments: params.arguments,
      userId: params.userId
    });
    return params;
  },
  
  afterExecute: async ({ result, toolSlug }) => {
    console.log(`[${new Date().toISOString()}] Completed ${toolSlug}`, {
      successful: result.successful,
      dataSize: JSON.stringify(result.data || {}).length
    });
    return result;
  }
};

Limitations

Modifiers must be synchronous or return Promises
Throwing errors in modifiers will prevent tool execution
Schema modifiers don’t validate the modified schema
Modifiers are not persisted and must be provided with each operation

Next Steps

Tool Execution

Apply modifiers to tool execution

Custom Tools

Use modifiers with custom tools

File Handling

Learn about automatic file upload/download modifiers

Error Handling

Handle errors in modifiers

Get Started

Core Concepts

Installation

Guides

MCP & Rube

Overview

Types of Modifiers

Schema Modifiers

Basic Schema Modification

Adding Custom Metadata

Modifying Input Parameters

Tool-Specific Modifications

Before Execute Modifiers

Basic Parameter Modification

Adding Authentication Headers

Conditional Parameter Transformation

Input Validation

After Execute Modifiers

Basic Response Transformation

Error Enhancement

Response Filtering and Enrichment

Logging and Monitoring

Combining Modifiers

Tool Router Meta Tool Modifiers

Best Practices

Keep Modifiers Pure

Handle Errors Gracefully

Use Type Safety

Performance Matters

Common Use Cases

Caching Responses

Rate Limiting

Request/Response Logging

Limitations

Next Steps

Tool Execution

Custom Tools

File Handling

Error Handling

​Overview

​Types of Modifiers

​Schema Modifiers

​Basic Schema Modification

​Adding Custom Metadata

​Modifying Input Parameters

​Tool-Specific Modifications

​Before Execute Modifiers

​Basic Parameter Modification

​Adding Authentication Headers

​Conditional Parameter Transformation

​Input Validation

​After Execute Modifiers

​Basic Response Transformation

​Error Enhancement

​Response Filtering and Enrichment

​Logging and Monitoring

​Combining Modifiers

​Tool Router Meta Tool Modifiers

​Best Practices

Keep Modifiers Pure

Handle Errors Gracefully

Use Type Safety

Performance Matters

​Common Use Cases

​Caching Responses

​Rate Limiting

​Request/Response Logging

​Limitations

​Next Steps

Tool Execution

Custom Tools

File Handling

Error Handling

Overview

Types of Modifiers

Schema Modifiers

Basic Schema Modification

Adding Custom Metadata

Modifying Input Parameters

Tool-Specific Modifications

Before Execute Modifiers

Basic Parameter Modification

Adding Authentication Headers

Conditional Parameter Transformation

Input Validation

After Execute Modifiers

Basic Response Transformation

Error Enhancement

Response Filtering and Enrichment

Logging and Monitoring

Combining Modifiers

Tool Router Meta Tool Modifiers

Best Practices

Common Use Cases

Caching Responses

Rate Limiting

Request/Response Logging

Limitations

Next Steps