Error Handling

The eBay MCP Server implements robust error handling at every layer to ensure reliable operation and provide clear feedback when issues occur. This guide explains the error handling strategies, common error scenarios, and recovery mechanisms.

Error Handling Philosophy

The server follows these principles for error handling:

Fail Fast - Detect errors as early as possible
Clear Messages - Provide actionable error messages with context
Automatic Recovery - Attempt automatic recovery when possible (e.g., token refresh)
Graceful Degradation - Fallback to alternative methods when primary method fails
Error Context - Include relevant details for debugging

Error Handling Layers

1. Input Validation Layer

All tool inputs are validated using Zod schemas before processing.

import { z } from 'zod';
import { MarketplaceId, FormatType } from '@/types/ebay-enums.js';

const createOfferSchema = z.object({
  sku: z.string().min(1, 'SKU is required'),
  marketplaceId: z.nativeEnum(MarketplaceId, {
    errorMap: () => ({ message: 'Invalid marketplace ID' })
  }),
  format: z.nativeEnum(FormatType),
  price: z.object({
    value: z.string().regex(/^\d+(\.\d{1,2})?$/, 'Invalid price format'),
    currency: z.string().length(3, 'Currency must be 3 characters'),
  }),
});

// Validation happens automatically
try {
  const validated = createOfferSchema.parse(input);
} catch (error) {
  // Zod provides detailed error with field-specific messages
  throw new Error(`Validation failed: ${error.message}`);
}

Benefits:

Catches invalid inputs before making API calls
Provides field-specific error messages
Prevents unnecessary API rate limit consumption
Type-safe validation

2. Authentication Error Handling

The OAuth client implements automatic token refresh and fallback strategies.

401 Unauthorized Errors

When a 401 error occurs, the server automatically attempts to refresh the access token.

// Response interceptor in src/api/client.ts (lines 106-165)
this.httpClient.interceptors.response.use(
  (response) => response,
  async (error: AxiosError) => {
    if (error.response?.status === 401) {
      const retryCount = config?.__authRetryCount || 0;

      // Only retry once to avoid infinite loops
      if (retryCount === 0 && config) {
        config.__authRetryCount = 1;

        console.error(
          'eBay API authentication error (401). Attempting to refresh user token...'
        );

        try {
          // Force token refresh
          const newToken = await this.authClient.getAccessToken();
          config.headers.Authorization = `Bearer ${newToken}`;

          console.error('Token refreshed successfully. Retrying request...');

          // Retry the request with new token
          return await this.httpClient.request(config);
        } catch (refreshError) {
          console.error('Failed to refresh token:', refreshError);

          throw new Error(
            `Authentication failed. Token refresh failed: ${refreshError.message}. ` +
            `Please use the ebay_set_user_tokens_with_expiry tool to provide valid tokens.`
          );
        }
      }

      // If retry already attempted, provide helpful error message
      throw new Error(
        `Authentication failed. Automatic token refresh failed. ` +
        `Please use the ebay_set_user_tokens_with_expiry tool to provide valid tokens.`
      );
    }

    // Other error handling...
  }
);

Error Flow:

API returns 401 Unauthorized
Server attempts to refresh access token
If refresh succeeds, request is retried automatically
If refresh fails, clear error message guides user to provide new tokens

Token Expiry Handling

The OAuth client checks token expiry before making requests (src/auth/oauth.ts:93-128).

async getAccessToken(): Promise<string> {
  // Try to use user token first
  if (this.userTokens) {
    // Check if access token is still valid
    if (!this.isUserAccessTokenExpired(this.userTokens)) {
      return this.userTokens.userAccessToken;
    }

    // Try to refresh if refresh token is valid
    if (!this.isUserRefreshTokenExpired(this.userTokens)) {
      try {
        await this.refreshUserToken();
        return this.userTokens.userAccessToken;
      } catch (error) {
        console.error('Failed to refresh user token, falling back to app access token:', error);
        this.userTokens = null;
      }
    } else {
      // Refresh token expired
      console.error('User refresh token expired. User needs to re-authorize.');
      this.userTokens = null;
      throw new Error(
        'User authorization expired. Please update EBAY_USER_REFRESH_TOKEN in .env with a new refresh token.'
      );
    }
  }

  // Fallback to app access token (client credentials)
  if (this.appAccessToken && Date.now() < this.appAccessTokenExpiry) {
    return this.appAccessToken;
  }

  await this.getOrRefreshAppAccessToken();
  return this.appAccessToken!;
}

Fallback Strategy:

Primary: User access token (if valid)
Secondary: Refresh user token (if access token expired)
Tertiary: App access token from client credentials

3. Rate Limit Error Handling

The server handles rate limits at two levels:

Client-Side Rate Limiting

Prevents requests when approaching rate limits (src/api/client.ts:15-44).

class RateLimitTracker {
  private requestTimestamps: number[] = [];
  private readonly windowMs = 60000; // 1 minute window
  private readonly maxRequests = 5000; // Conservative limit

  canMakeRequest(): boolean {
    const now = Date.now();
    // Remove timestamps older than window
    this.requestTimestamps = this.requestTimestamps.filter(
      (timestamp) => now - timestamp < this.windowMs
    );
    return this.requestTimestamps.length < this.maxRequests;
  }

  recordRequest(): void {
    this.requestTimestamps.push(Date.now());
  }
}

// Check before making request
if (!this.rateLimitTracker.canMakeRequest()) {
  const stats = this.rateLimitTracker.getStats();
  throw new Error(
    `Rate limit exceeded: ${stats.current}/${stats.max} requests in ${stats.windowMs}ms window. ` +
    `Please wait before making more requests.`
  );
}

Server-Side Rate Limit Handling (429)

When eBay API returns 429, the server provides clear guidance (src/api/client.ts:168-176).

if (error.response?.status === 429) {
  const retryAfter = error.response.headers['retry-after'];
  const waitTime = retryAfter ? parseInt(retryAfter) * 1000 : 60000;

  throw new Error(
    `eBay API rate limit exceeded. Retry after ${waitTime / 1000} seconds. ` +
    `Consider reducing request frequency or upgrading to user tokens for higher limits.`
  );
}

4. Server Error Handling (5xx)

The server implements automatic retry with exponential backoff for server errors (src/api/client.ts:179-194).

if (error.response?.status && error.response.status >= 500 && config) {
  const retryCount = config.__retryCount || 0;

  if (retryCount < 3) {
    config.__retryCount = retryCount + 1;
    const delay = Math.pow(2, retryCount) * 1000; // Exponential backoff

    console.error(
      `eBay API server error (${error.response.status}). ` +
      `Retrying in ${delay}ms (attempt ${retryCount + 1}/3)...`
    );

    await new Promise((resolve) => setTimeout(resolve, Math.min(delay, 5000)));
    return await this.httpClient.request(config);
  }
}

Retry Strategy:

Attempt 1: Immediate retry (0ms delay)
Attempt 2: 2 second delay
Attempt 3: 4 second delay
Maximum delay: 5 seconds (capped)

5. eBay API Error Handling

eBay API errors are transformed into clear, actionable messages (src/api/client.ts:196-204).

if (axios.isAxiosError(error) && error.response?.data) {
  const ebayError = error.response.data as EbayApiError;
  const errorMessage =
    ebayError.errors?.[0]?.longMessage ||
    ebayError.errors?.[0]?.message ||
    error.message;
  throw new Error(`eBay API Error: ${errorMessage}`);
}

eBay Error Format:

{
  "errors": [
    {
      "errorId": 123,
      "domain": "API_INVENTORY",
      "category": "REQUEST",
      "message": "Invalid SKU format",
      "longMessage": "The SKU 'test sku' contains invalid characters. SKUs must be alphanumeric.",
      "parameters": [
        {
          "name": "sku",
          "value": "test sku"
        }
      ]
    }
  ]
}

6. MCP Tool Error Handling

The MCP server wraps all tool executions with error handling (src/index.ts:42-66).

this.server.registerTool(
  toolDef.name,
  {
    description: toolDef.description,
    inputSchema: toolDef.inputSchema,
  },
  async (args: Record<string, unknown>) => {
    try {
      const result = await executeTool(this.api, toolDef.name, args);
      return {
        content: [
          {
            type: 'text' as const,
            text: JSON.stringify(result, null, 2),
          },
        ],
      };
    } catch (error) {
      const errorMessage = error instanceof Error ? error.message : 'Unknown error';

      return {
        content: [
          {
            type: 'text' as const,
            text: JSON.stringify({ error: errorMessage }, null, 2),
          },
        ],
        isError: true,
      };
    }
  }
);

Error Response Format:

{
  "error": "eBay API Error: The SKU 'test sku' contains invalid characters."
}

Common Error Scenarios

1. Missing Access Token

Error:

Access token is missing. Please provide your access token and refresh token by calling ebay_set_user_tokens tool in order to perform API requests.

Cause: No user tokens configured. Solutions:

Via .env File (Recommended)
Via MCP Tool
Generate New Tokens

# Add to .env file
EBAY_USER_REFRESH_TOKEN=v^1.1#i^1#...
EBAY_USER_ACCESS_TOKEN=v^1.1#i^1#...

# Run auto-setup
npm run auto-setup

# Restart MCP client

Use the ebay_set_user_tokens_with_expiry tool with:
- accessToken: Your user access token
- refreshToken: Your user refresh token
- accessTokenExpiry: Token expiration timestamp

Note: Tokens set via tool are memory-only and lost on restart

Use ebay_get_oauth_url tool to generate authorization URL
Open URL in browser and authorize
Exchange authorization code for tokens
Add tokens to .env file

2. Expired Refresh Token

Error:

User authorization expired. Please update EBAY_USER_REFRESH_TOKEN in .env with a new refresh token.

Cause: Refresh token has expired (typically after 18 months). Solution:

Generate new OAuth URL with ebay_get_oauth_url tool
Complete authorization flow
Update .env file with new refresh token
Restart server

3. Invalid SKU Format

Error:

eBay API Error: The SKU 'test sku' contains invalid characters. SKUs must be alphanumeric.

Cause: SKU contains spaces or special characters. Solution: Use alphanumeric SKUs without spaces:

// ❌ Bad
sku: "test sku"
sku: "test-sku!"

// ✅ Good
sku: "TEST_SKU_001"
sku: "TESTSKU001"

4. Rate Limit Exceeded

Error:

Rate limit exceeded: 5000/5000 requests in 60000ms window. Please wait before making more requests.

Cause: Too many requests in short time period. Solutions:

Wait for rate limit window to reset
Upgrade to user tokens (10,000-50,000 req/day vs. 1,000 with client credentials)
Reduce request frequency
Implement request batching

5. Network Timeout

Error:

timeout of 30000ms exceeded

Cause: Request took longer than 30 seconds. Solutions:

Check network connectivity
Try again later (may be temporary eBay API issue)
For bulk operations, break into smaller batches

6. Validation Errors

Error:

Validation failed: Invalid type: expected string, received number at "price.value"

Cause: Input doesn’t match expected schema. Solution: Ensure all inputs match the expected types:

// ❌ Bad
{
  price: {
    value: 19.99,  // Number
    currency: "USD"
  }
}

// ✅ Good
{
  price: {
    value: "19.99",  // String
    currency: "USD"
  }
}

Error Recovery Strategies

Automatic Recovery

The server automatically recovers from:

Expired Access Tokens - Automatically refreshes using refresh token
Server Errors (5xx) - Retries with exponential backoff (up to 3 attempts)
Network Timeouts - Can be retried manually

Manual Recovery

Some errors require manual intervention:

Expired Refresh Tokens - Requires new OAuth authorization
Invalid Credentials - Update .env file with correct credentials
Validation Errors - Fix input data
Permission Errors - Update eBay app scopes

Graceful Degradation

The server implements fallback strategies:

User Token → App Token - Falls back to client credentials if user token unavailable
Partial Data - Returns partial results when bulk operations partially fail
Default Values - Uses sensible defaults when optional parameters missing

Error Logging

The server logs errors to stderr for monitoring:

// Authentication errors
console.error('eBay API authentication error (401). Attempting to refresh user token...');
console.error('Token refreshed successfully. Retrying request...');
console.error('Failed to refresh token:', refreshError);

// Rate limit warnings
console.error(`eBay Rate Limit: ${remaining}/${limit} remaining`);

// Server errors
console.error(
  `eBay API server error (${status}). Retrying in ${delay}ms (attempt ${retryCount + 1}/3)...`
);

Log Levels:

Error: Authentication failures, API errors, rate limits
Warning: Token refresh, retry attempts
Info: Server startup, configuration validation

Debugging Errors

Enable Debug Mode

# In .env file
EBAY_DEBUG=true

This provides additional logging for:

Request/response details
Token expiry timestamps
Rate limit statistics
Retry attempts

Check Token Status

// Use ebay_get_token_status tool
{
  "hasUserTokens": true,
  "tokenType": "User",
  "accessTokenExpiry": "2025-11-16T12:00:00.000Z",
  "refreshTokenExpiry": "2027-05-16T10:00:00.000Z",
  "scopes": [
    "https://api.ebay.com/oauth/api_scope/sell.account",
    "https://api.ebay.com/oauth/api_scope/sell.inventory"
  ]
}

Check Rate Limit Statistics

// Get rate limit stats from client
const stats = client.getRateLimitStats();
// {
//   current: 4523,
//   max: 5000,
//   windowMs: 60000
// }

Review Error Context

All errors include context:

{
  "error": "eBay API Error: Invalid SKU format",
  "details": {
    "errorId": 25002,
    "domain": "API_INVENTORY",
    "category": "REQUEST",
    "parameters": [
      { "name": "sku", "value": "test sku" }
    ]
  }
}

Best Practices

1. Always Handle Errors

// ✅ Good
try {
  const result = await api.inventory.getInventoryItem(sku);
  return result;
} catch (error) {
  console.error('Failed to get inventory item:', error);
  // Handle error appropriately
  throw error;
}

// ❌ Bad
const result = await api.inventory.getInventoryItem(sku);
return result;

2. Validate Inputs Early

// ✅ Good
const schema = z.object({
  sku: z.string().min(1),
  quantity: z.number().int().min(0),
});

const validated = schema.parse(input);
await api.inventory.createInventoryItem(validated.sku, validated);

// ❌ Bad
await api.inventory.createInventoryItem(input.sku, input);

3. Provide Context in Errors

// ✅ Good
throw new Error(`Failed to create offer for SKU "${sku}": ${error.message}`);

// ❌ Bad
throw new Error(error.message);

4. Use Appropriate Error Types

class RateLimitError extends Error {
  constructor(message: string, public retryAfter: number) {
    super(message);
    this.name = 'RateLimitError';
  }
}

class AuthenticationError extends Error {
  constructor(message: string) {
    super(message);
    this.name = 'AuthenticationError';
  }
}

5. Don’t Expose Sensitive Information

// ✅ Good
throw new Error('Authentication failed. Please check credentials.');

// ❌ Bad
throw new Error(`Authentication failed. Client ID: ${clientId}, Secret: ${clientSecret}`);

Architecture

Understand the error handling architecture

Rate Limits

Learn about rate limiting and strategies

Troubleshooting

Common issues and solutions

OAuth Setup

Configure authentication properly

​Error Handling

​Error Handling Philosophy

​Error Handling Layers

​1. Input Validation Layer

​2. Authentication Error Handling

​401 Unauthorized Errors

​Token Expiry Handling

​3. Rate Limit Error Handling

​Client-Side Rate Limiting

​Server-Side Rate Limit Handling (429)

​4. Server Error Handling (5xx)

​5. eBay API Error Handling

​6. MCP Tool Error Handling

​Common Error Scenarios

​1. Missing Access Token

​2. Expired Refresh Token

​3. Invalid SKU Format

​4. Rate Limit Exceeded

​5. Network Timeout

​6. Validation Errors

​Error Recovery Strategies

​Automatic Recovery

​Manual Recovery

​Graceful Degradation

​Error Logging

​Debugging Errors

​Enable Debug Mode

​Check Token Status

​Check Rate Limit Statistics

​Review Error Context

​Best Practices

​1. Always Handle Errors

​2. Validate Inputs Early

​3. Provide Context in Errors

​4. Use Appropriate Error Types

​5. Don’t Expose Sensitive Information

​Related Topics

Architecture

Rate Limits

Troubleshooting

OAuth Setup

Error Handling

Error Handling Philosophy

Error Handling Layers

1. Input Validation Layer

2. Authentication Error Handling

401 Unauthorized Errors

Token Expiry Handling

3. Rate Limit Error Handling

Client-Side Rate Limiting

Server-Side Rate Limit Handling (429)

4. Server Error Handling (5xx)

5. eBay API Error Handling

6. MCP Tool Error Handling

Common Error Scenarios

1. Missing Access Token

2. Expired Refresh Token

3. Invalid SKU Format

4. Rate Limit Exceeded

5. Network Timeout

6. Validation Errors

Error Recovery Strategies

Automatic Recovery

Manual Recovery

Graceful Degradation

Error Logging

Debugging Errors

Enable Debug Mode

Check Token Status

Check Rate Limit Statistics

Review Error Context

Best Practices

1. Always Handle Errors

2. Validate Inputs Early

3. Provide Context in Errors

4. Use Appropriate Error Types

5. Don’t Expose Sensitive Information

Related Topics