MCP Gateway

MCP Gateway

Enterprise multi-server MCP (Model Context Protocol) gateway providing centralized health monitoring, rate limiting, audit logging, and approval workflows for managed MCP servers.

Architecture

Four files in src/mcp-gateway/:

File	Purpose
types.ts	Data types: McpServerEntry, HealthCheckResult, AuditLogEntry, ApprovalRequest, GatewayConfig
gateway.ts	Core gateway: rate limiter, health checks, audit logging, risk assessment
registry.ts	Server registry: CRUD, filtering by tag/transport/health status
mod.ts	Module barrel exports

Health Checks

healthCheck() probes each registered HTTP MCP server by sending a tools/list JSON-RPC call. Results include:

Status	Criteria
healthy	Server responds and tool count matches registered count
degraded	Server responds but tool count differs
unhealthy	Server unreachable or returns error
unknown	Stdio transport (not checkable via HTTP)

Health check timeout: 10 seconds. Latency is recorded for each check.

Rate Limiting

Token bucket rate limiter (createRateLimiter()):

Parameter	Description
maxRequestsPerMinute	Maximum requests per minute per key
Tokens refill	At rate of maxRequestsPerMinute / 60 per second
Key	Arbitrary string (typically client ID or server ID)

const limiter = createRateLimiter({ maxRequestsPerMinute: 60 });
limiter.allowRequest("client-abc"); // → boolean
limiter.getAvailableTokens("client-abc"); // → number

Audit Logging

All tool calls through the gateway are logged:

Field	Description
id	UUID
timestamp	ISO 8601
serverId	MCP server ID
toolName	Executed tool
clientId	Requesting client
success	Whether execution succeeded
latencyMs	Response latency
errorCode	Error code if failed
tokensUsed	LLM tokens consumed

In-memory ring buffer with 10,000 entry cap. Filterable by serverId.

Approval Workflow

Risk Levels

assessRiskLevel() evaluates tool calls against pattern matching:

Level	Criteria
low	Read-only tools, safe operations
medium	Tools containing write, delete, shell, exec
high	rm -rf, DROP TABLE, DELETE FROM, format, shutdown, kill, terminate
critical	DROP DATABASE, rm -rf /, TRUNCATE

Approval Requests

Field	Description
id	UUID
serverId	Target server
toolName	Tool being invoked
args	Tool arguments
riskLevel	Assessed risk
requestedBy	Client identifier
status	pending / approved / denied / expired

Configure which risk levels require approval: approvalRequiredForRisk: ["medium", "high", "critical"].

Server Registry

In-memory registry with CRUD operations:

Function	Description
registerServer(entry)	Add server
getServer(id)	Get by ID
listServers()	All servers
findServersByTag(tag)	Filter by tag
updateServer(id, updates)	Partial update
removeServer(id)	Delete
getHealthyServers()	Status === healthy
getDegradedServers()	Status === degraded or unhealthy
getServersByTransport(type)	Filter by stdio or http

MCP Auto-Discovery

Gateway-managed servers expose their tools through the MCP protocol. The gateway discovers available tools by calling tools/list on each registered server during health checks, storing discovered tool names and counts.

Configuration

{
  "mcpGateway": {
    "enabled": true,
    "defaultRateLimit": {
      "maxRequestsPerMinute": 60,
      "burstSize": 10
    },
    "auditEnabled": true,
    "approvalRequiredForRisk": ["high", "critical"]
  }
}

McpServerEntry Schema

{
  id: string;
  name: string;
  endpoint: string;
  transport: "stdio" | "http";
  status: "healthy" | "degraded" | "unhealthy" | "unknown";
  lastHealthCheck: string;          // ISO 8601
  authType?: "none" | "oauth2" | "apiKey" | "bearer";
  authConfig?: Record<string, string>;
  tools: string[];                  // Discovered tool names
  toolCount: number;
  rateLimit?: RateLimitConfig;
  tags?: string[];
  createdAt: string;
  updatedAt: string;
}

REST API Endpoints

Method	Path	Description
GET	/api/mcp-gateway/servers	List all registered servers
POST	/api/mcp-gateway/servers	Register new server
GET	/api/mcp-gateway/servers/:id	Get server details
PUT	/api/mcp-gateway/servers/:id	Update server
DELETE	/api/mcp-gateway/servers/:id	Remove server
POST	/api/mcp-gateway/servers/:id/health	Trigger health check
GET	/api/mcp-gateway/audit	Get audit logs (filter: ?serverId=)
POST	/api/mcp-gateway/approvals	Submit approval decision

See Also

• A2A Protocol — A2A protocol with similar tool-wrapping pattern
• Distributed Nodes — Hub security model and capability tiers
• Triggers — Event-driven automation system