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:

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.
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

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

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

Native Charter MCP

Veto also exposes Charter as a native MCP JSON-RPC surface. This is not an upstream proxy; it is Veto Cloud's own policy agent for Claude Code, Cursor, and other MCP-capable agents.

Endpoint:

POST https://api.veto.so/v1/mcp/charter

List tools:

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

Available tools:

veto_charter_turn, run a Charter turn with mode: auto | chat | compile
veto_charter_chat, ask grounded questions about registered tools, policies, and runtime context
veto_charter_compile, draft policies and return Veto verification links before anything goes live
veto_list_tools, list the tools Charter can compile against
veto_register_tools, register an agent's callable tools before Charter compiles policies

curl -X POST https://api.veto.so/v1/mcp/charter \
  -H 'X-Veto-API-Key: veto_xxx' \
  -H 'content-type: application/json' \
  -d '{
    "jsonrpc": "2.0",
    "id": "register-tools",
    "method": "tools/call",
    "params": {
      "name": "veto_register_tools",
      "arguments": {
        "tools": [
          {
            "name": "issue_refund",
            "description": "Issue a customer refund",
            "parameters": [
              { "name": "amount_usd", "type": "number", "required": true },
              { "name": "ticket_age_days", "type": "number", "required": true }
            ]
          }
        ]
      }
    }
  }'

Example compile call:

curl -X POST https://api.veto.so/v1/mcp/charter \
  -H 'X-Veto-API-Key: veto_xxx' \
  -H 'content-type: application/json' \
  -d '{
    "jsonrpc": "2.0",
    "id": "compile-refunds",
    "method": "tools/call",
    "params": {
      "name": "veto_charter_compile",
      "arguments": {
        "message": "Refunds over $200 require support lead approval."
      }
    }
  }'

Policy-changing responses include structuredContent.verification. A policy draft is not live until the returned Veto verification link is approved.

Operational smoke check:

VETO_API_KEY=veto_xxx node ops/smoke/charter-agent-surfaces.mjs

By default, the script verifies read-only Charter MCP discovery. Set VETO_CHARTER_SMOKE_WRITE=1 to also register a probe tool, and VETO_CHARTER_SMOKE_COMPILE=1 to verify compile returns a review link.