MCP Gateway

Veto MCP Gateway lets you enforce Veto policies on MCP tools/call traffic while preserving normal MCP JSON-RPC behavior.

Architecture

Veto MCP Gateway has two launch paths:

1. Managed gateway in veto-server:
   • Configure upstreams in the dashboard.
   • Call POST /v1/mcp/:slug (and optional GET /v1/mcp/:slug SSE stream).
   • Data path auth uses your Veto API key.
2. Self-hosted gateway in CLI:
   • Run veto mcp serve.
   • Route MCP requests to configured upstreams from veto/mcp.config.yaml.
   • Supports mcp-sse and mcp-stdio.

Policy decisions map to JSON-RPC responses:

• allow: upstream call is forwarded.
• deny: JSON-RPC error -32001.
• require_approval: JSON-RPC error -32002.

Self-hosted quickstart

Initialize config:

veto mcp init

Generated file:

listen:
  host: 127.0.0.1
  port: 8799
policy:
  serverUrl: http://localhost:3001
  apiKey: veto_replace_me
upstreams:
  - name: default
    transport: mcp-sse
    url: http://localhost:3000/mcp
    timeoutMs: 30000

Run diagnostics:

veto mcp doctor
veto mcp doctor --json

Start gateway:

veto mcp serve --config ./veto/mcp.config.yaml

You can also run without a config file for simple SSE setups:

veto mcp serve \
  --upstream http://localhost:3000/mcp \
  --api-key veto_xxx \
  --policy-server http://localhost:3001

Managed quickstart

1. Open dashboard settings and go to MCP Gateway.
2. Add an upstream slug and transport (mcp-sse in managed mode).
3. Test connectivity from the UI.
4. Send MCP JSON-RPC to:

curl -X POST https://api.runveto.com/v1/mcp/default \
  -H 'X-Veto-API-Key: veto_xxx' \
  -H 'content-type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Managed vs self-hosted transport support

• Managed v1 supports: mcp-sse.
• Self-hosted supports: mcp-sse, mcp-stdio.

If you need stdio for local process adapters, run self-hosted veto mcp serve.

Troubleshooting

SSE upstream timeouts

Symptoms:

• Upstream timeout
• No response in SSE stream

Checks:

• Increase timeoutMs for the upstream.
• Verify upstream endpoint accepts JSON-RPC POST payloads.
• Confirm upstream returns matching JSON-RPC id in responses.

Policy server unreachable

Symptoms:

• Policy server unreachable
• doctor reports policy server probe failure.

Checks:

• Verify policy.serverUrl.
• Verify policy.apiKey starts with veto_ and is valid.
• Confirm POST /v1/validate is reachable from gateway runtime.

Stdio differences

Symptoms:

• Managed upstream creation rejected for mcp-stdio.

Cause:

• Managed v1 intentionally blocks stdio transports.

Resolution:

• Move that upstream to self-hosted veto mcp serve.

Related

• CLI reference
• MCP API reference
• MCP SDK integration