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Grand Central can proxy external MCP servers, giving you a unified endpoint for both Grand Central’s API-backed tools and third-party MCP servers. This provides consistent security, auditing, and cost control across all your AI agent’s capabilities.

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What are external MCP servers?

External MCP servers are MCP-compatible services hosted outside Grand Central. Third-party services come from other vendors offering specialized MCP capabilities. Open source tools are community-maintained MCP servers that provide free functionality. Partner integrations use MCP servers from Grand Central’s technology partners with pre-negotiated access. Custom servers include your organization’s own MCP servers hosted elsewhere that you want to access through Grand Central’s unified interface.

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Why route through Grand Central?

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Unified authentication

Single credential management means your Grand Central API key works for all servers - no need to manage multiple API keys across different services. This eliminates credential sprawl and simplifies your agent’s authentication logic. Centralized access control through the admin portal lets you enable or disable external servers without changing your agent’s configuration.

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Consistent security

Centralized audit trails log all tool invocations regardless of whether they target Grand Central’s native APIs or external MCP servers. Unified rate limiting applies the same controls across internal and external tools, preventing any single integration from monopolizing your quota. Single compliance point means security policies, monitoring rules, and access controls apply consistently across all MCP capabilities.

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Cost control

Usage tracking shows costs across all external MCP server calls in a single dashboard, making it easy to identify expensive integrations. Budget enforcement prevents unexpected charges from third-party services by setting spending limits per external server. Consolidated billing means one invoice for all MCP usage - both native Grand Central tools and external servers - simplifying accounting and cost allocation.

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Available external servers

External servers available through Grand Central vary by organization. Common examples include weather services (real-time weather data and forecasts), search engines (web search and knowledge retrieval), data analytics tools (statistical analysis and visualization), and file conversion services (document format transformation). Your specific installation may have different external servers configured based on organizational needs and vendor partnerships.
Check the admin portal to see available external MCP servers. Request access to additional servers through the portal - external server requests typically require manual review due to cost and compliance implications.

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How to use external servers

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1. Check availability

Log into the admin portal and navigate to the External Servers section to view available third-party MCP servers. The portal shows currently enabled external servers, available servers pending configuration, detailed server descriptions and capabilities, and cost implications per server. Filter by category (weather services, search engines, document processing, etc.) to find servers matching your needs.

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2. Request access

If an external server isn’t available yet, submit a request through the admin portal: Server Configuration Form: 
Server: Weather MCP (weather-mcp.example.com)
Use Case: AI agent needs real-time weather for trip planning
Expected Usage: ~500 calls/day
Business Justification: Customer-facing travel assistant
Cost Approval: Confirm budget allocation
External server requests typically require manual review (3 to 5 business days) because they involve third-party costs, compliance implications, and vendor relationship management.

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3. Connect your AI agent

Once enabled, external servers appear in your tool list alongside Grand Central’s native tools: 
{
  "mcpServers": {
    "grand-central": {
      "url": "https://your-instance.example.com/mcp",
      "headers": {
        "Ocp-Apim-Subscription-Key": "your-api-key"
      }
    }
  }
}
Your AI agent will automatically discover tools from both Grand Central’s API-backed tools (e.g., get_customer, create_order) and external MCP servers (e.g., get_weather, search_web) through the standard tool discovery process.

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4. Monitor usage

External server calls appear in your usage dashboard with comprehensive metrics. Call count shows the number of invocations to each external server, helping you understand usage patterns. Response times compare latency for external versus internal tools so you can identify performance bottlenecks. Costs track charges from third-party services if any apply to your external servers. Errors highlight failed calls to external servers, making troubleshooting straightforward.

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Authentication handling

Grand Central manages authentication to external servers transparently:

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For your AI agent

Your agent uses a single API key - your Grand Central subscription key - for everything. You never handle external credentials directly, meaning no external server API keys in your configuration files or code. The consistent interface applies the same authentication method for all tools, whether they come from Grand Central’s APIs or external MCP servers.

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Behind the scenes

Grand Central handles forwarding authentication to external servers, managing API keys for third-party services, token refresh and expiration handling, and credential rotation for security. All of this happens transparently without requiring any configuration in your agent code.
You never see or manage external server credentials. This prevents credential leakage and simplifies your AI agent’s security model.

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Best practices

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Start with native tools

Prefer Grand Central’s API-backed tools when available - they’re faster, cheaper, and better integrated with your platform. Only add external servers when Grand Central doesn’t provide the capability you need. External servers may have different latency and reliability characteristics than native tools, so monitor their performance carefully and implement fallback strategies where appropriate.

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Understand cost implications

Grand Central native tools are included in your platform subscription with predictable costs based on which Grand Central APIs you’re calling. External MCP servers may incur per-call charges from third-party vendors, and costs vary significantly by external service provider. Review cost details in the admin portal before enabling high-volume usage to avoid budget surprises.

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Handle external server failures

External servers can be unreachable: 
# Example: graceful degradation
try:
    weather = agent.call_tool("get_weather", {"location": "NYC"})
except ToolExecutionError as e:
    if "weather-mcp" in str(e):
        # External weather server unavailable
        weather = "Weather unavailable, proceeding without forecast"
Common issues include external server downtime (not under Grand Central’s control), rate limiting from the third-party service, authentication failures to the external provider, and network connectivity issues between Grand Central and the external server.

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Security considerations

When your AI agent calls an external MCP server tool, the tool parameters are sent to that third-party service. Be mindful of sensitive customer data, proprietary business information, and compliance requirements (GDPR, HIPAA, etc.) that may restrict what data can leave your environment.Recommendation: Review external server privacy policies (linked in admin portal) before sending sensitive data. Contact your security team if you have compliance concerns.
Grand Central logs which external server was called, the tool name and timestamp, and response status (success or failure). However, Grand Central does NOT log tool parameter values (to protect sensitive data) or full response bodies from external servers.Recommendation: For detailed external server auditing, check if the third-party service provides its own logs.
Grand Central’s compliance certifications (SOC 2, ISO 27001, etc.) cover the proxy infrastructure but NOT external third-party MCP servers.Recommendation: Verify that external MCP servers meet your organization’s compliance requirements separately.

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Requesting new external servers

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Evaluation criteria

When you submit a request through the admin portal, automated validation and manual reviewers evaluate several factors. Security practices must be acceptable - does the external MCP server follow industry standards? Reliability matters - what’s the uptime SLA, and can it handle your expected usage volume? Cost implications include per-call charges and minimum commitments that affect your budget. Compliance alignment ensures the external server meets your organization’s regulatory requirements. Support coverage clarifies what happens when the external server has issues and who’s responsible for resolution.

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Request template

Subject: New External MCP Server Request

External Server Details:
- Name: [Server Name]
- Provider: [Company/Project]
- Documentation: [URL]
- MCP Protocol Version: [e.g., 1.0.0]

Business Case:
- Use Case: [What AI agent capability does this enable?]
- Expected Volume: [Calls per day/week]
- Timeline: [When do you need this?]

Security & Compliance:
- Data Sensitivity: [What data will be sent?]
- Compliance Requirements: [GDPR, HIPAA, SOC 2, etc.]

Cost Considerations:
- External Service Pricing: [Free, $X per call, etc.]
- Budget Approval: [Yes/No, Pending]

Please evaluate for addition to Grand Central's external server catalog.

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Troubleshooting

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Tool not available

Symptom: AI agent doesn’t see expected external server tools Possible Causes: The external server may not be configured in Grand Central yet, your subscription might not include access to that server, or the external server could be temporarily disabled for maintenance. Resolution: Check admin portal to verify external server status and your subscription’s access level

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Slow response times

Symptom: External server tools take longer than Grand Central native tools Possible Causes: Geographic distance to the external server, high load on the external server, or network latency to the third-party service can all contribute to slower response times. Resolution: Check monitoring dashboard for external server latency metrics to understand baseline performance. Consider caching external server responses if appropriate for your use case to reduce latency on repeated calls. Check admin portal to see if alternative server regions are available that might offer better performance.

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Authentication errors

Symptom: External server tools fail with authentication errors Possible Causes: Grand Central’s credentials to the external server may have expired, the external server may have rotated API keys without notification, or the external server’s authentication service could be experiencing an outage. Resolution: External server credentials are managed centrally - check the admin portal’s system status page or submit a support request if authentication persists

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Unexpected costs

Symptom: Higher than expected charges for external MCP server usage Possible Causes: The external service may have per-call pricing you weren’t fully aware of, your AI agent might be calling external tools more frequently than anticipated, or the external service could have changed their pricing model. Resolution: Review usage dashboard to identify high-volume external tools that are driving costs. Optimize AI agent prompt to reduce unnecessary external calls - sometimes agents call expensive tools when cached data would suffice. Check admin portal for current external server pricing and usage forecasts to understand cost trends and plan budget accordingly.

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FAQ

No - only external MCP servers that have been configured and approved through the admin portal. This ensures security, cost control, and compliance.
Yes - calls to external MCP servers count toward your Grand Central rate limits. However, any per-call charges from the external service are separate.
Your AI agent will receive an error when calling tools from that server. Grand Central’s native tools continue working normally. Implement graceful degradation in your agent to handle external server unavailability.
Technically yes, but you lose centralized auditing, unified authentication, cost tracking, and rate limiting. Most organizations require all MCP access to go through Grand Central for governance.
The tool discovery response doesn’t distinguish between native and external tools - this is intentional to provide a unified interface. Check your usage dashboard to see which external servers are being called.

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Next steps

Monitor external usage

Track performance and costs for external MCP servers

Best practices

Optimize AI agent behavior with external tools

Limitations

Understand Grand Central platform constraints

Getting started

Learn how to request MCP access