Keypost - MCP Policy Enforcement

2 min read Original article ↗

Policy enforcement for MCP pipelines

Add guardrails for agent tool calling. Enforce access control, rate limits, and cost management across MCP pipelines without code changes. Swap one URL and you're protected.

How it works: deterministic, in-path policy enforcement → View the policy model

The Problem

MCP servers expose powerful tools with zero restrictions

GitHub, Slack, databases - these integrations give AI agents direct access to production systems with no access controls, no rate limits, no audit trail.

One misconfigured agent can delete repositories, spam customers, or rack up unexpected API costs. You need guardrails before going to production.

Comprehensive Policy Enforcement

Protect your systems with flexible, composable policies

Access Control

Allow or deny specific tools with granular permissions

  • • Allowlist dangerous operations
  • • Role-based access rules
  • • Tool-level permissions

Parameter Constraints

Validate and restrict parameter values

  • • Regex pattern matching
  • • Value ranges and blocklists
  • • Type validation

Time-based Restrictions

Schedule tool availability by day and time

  • • Business hours enforcement
  • • Prevent weekend deployments
  • • Timezone-aware rules

DLP & PII Scanning

Block sensitive data patterns automatically

  • • SSN, credit card detection
  • • API key scanning
  • • Custom pattern blocking

Rate Limiting

Control request frequency at multiple levels

  • • Per-minute/hour/day quotas
  • • User & team-level limits
  • • Recipient-based throttling

Cost Management

Track and limit spending by team or project

  • • Budget tracking & alerts
  • • Response caching with TTL
  • • Cost attribution tags

Built for Performance

Rust-powered policy enforcement designed for speed and reliability

< 2ms

Policy Overhead

Typical policy evaluation adds minimal latency

10,000+

Requests per Second

Single instance throughput for high-scale deployments

< 5ms

P99 Latency

End-to-end response time at the 99th percentile

Architecture Highlights

Streaming Support

SSE passthrough for real-time responses

Zero-downtime Policy Updates

Change rules instantly without restarting or dropping requests

Full MCP Protocol Compliance

Works seamlessly with Claude Desktop, Cursor, and any MCP-compatible agent

Multi-tenant Isolation

Secure policy namespaces with team-level separation

Built on Rust and Tokio. Performance targets based on architecture design.

Ready to secure your MCP pipeline?

Start adding guardrails to your AI agent tool calls