MCP Spine

The middleware layer MCP is missing. Security, routing, token control, and compliance — between your LLM and your tools.

MCP Spine is a local-first proxy that sits between Claude Desktop (or any MCP client) and your MCP servers. One config, one entry point, full control over what goes in, what comes out, and what gets logged.

57 tools across 5 servers. One proxy. Zero tokens wasted.

The Problem

You've connected Claude to GitHub, Slack, your database, your filesystem. Now you have 40+ tools loaded, thousands of tokens burned on schemas every turn, no audit trail, no rate limits, and no way to stop the LLM from reading your boss's DMs. MCP gives agents power. Spine gives you control.

Related MCP server: mcp-doorman

What It Does

Demo

Runs on Windows, macOS, and Linux. CI tested across all three.

Web Dashboard

mcp-spine web --db spine_audit.db

Install

pip install mcp-spine

# With semantic routing (optional)
pip install mcp-spine[ml]

Quick Start

# Interactive setup wizard — detects your servers, asks about features
mcp-spine init

# Or quick default config
mcp-spine init --quick

# Check everything works
mcp-spine doctor --config spine.toml

# Start the proxy
mcp-spine serve --config spine.toml

# Open the web dashboard
mcp-spine web --db spine_audit.db

# Export analytics
mcp-spine export --format csv --hours 24 --output report.csv

Claude Desktop Integration

Replace all your individual MCP server entries with a single Spine entry:

{
  "mcpServers": {
    "spine": {
      "command": "python",
      "args": ["-m", "spine.cli", "serve", "--config", "/path/to/spine.toml"],
      "cwd": "/path/to/mcp-spine"
    }
  }
}

Features

Security Proxy (Stage 1)

• JSON-RPC message validation and sanitization

• Secret scrubbing (AWS keys, GitHub tokens, bearer tokens, private keys, connection strings)

• Per-tool and global rate limiting with sliding windows

• Path traversal prevention with symlink-aware jail

• Command injection guards for server spawning

• HMAC-fingerprinted SQLite audit trail

• Circuit breakers on failing servers

• Declarative security policies from config

Semantic Router (Stage 2)

• Local vector embeddings using all-MiniLM-L6-v2 (no API calls, no data leaves your machine)

• ChromaDB-backed tool indexing

• Query-time routing: only the most relevant tools are sent to the LLM

• spine_set_context meta-tool for explicit context switching

• Keyword overlap + recency boost reranking

• Background model loading — tools work immediately, routing activates when ready

Schema Minification (Stage 3)

• 4 aggression levels (0=off, 1=light, 2=standard, 3=aggressive)

• Level 2 achieves 61% token savings on tool schemas

• Strips $schema, titles, additionalProperties, parameter descriptions, defaults

• Preserves all required fields and type information

• Token savings tracked in audit trail and visible in web dashboard

State Guard (Stage 4)

• Watches project files via watchfiles

• Maintains SHA-256 manifest with monotonic versioning

• Injects compact state pins into tool responses

• Prevents LLMs from editing stale file versions

Human-in-the-Loop

• require_confirmation policy flag for destructive tools

• Spine intercepts the call, shows the arguments, and waits for user approval

• spine_confirm / spine_deny meta-tools for the LLM to relay the decision

• Per-tool granularity via glob patterns

Tool Output Memory

• Ring buffer caching last 50 tool results

• Deduplication by tool name + argument hash

• TTL expiration (1 hour default)

• spine_recall meta-tool to query cached results

• Prevents context loss when semantic router swaps tools between turns

Token Budget

• Daily token consumption tracking across all tool calls

• Configurable daily limit with warn/block actions

• Per-server token limits for cost control

• Persistent SQLite storage (survives restarts within the same day)

• Automatic midnight rollover

• spine_budget meta-tool to check usage mid-conversation

Plugin System

• Drop-in Python plugins that hook into the tool call pipeline

• Four hook points: on_tool_call, on_tool_response, on_tool_list, on_startup/on_shutdown

• Plugins can transform arguments, filter responses, block calls, or hide tools

• Plugin chaining — multiple plugins run in sequence

• Allow/deny lists for plugin access control

• Auto-discovery from a configurable plugins directory

• Example included: Slack channel compliance filter

Prompt Injection Detection

• Scans all tool responses before they reach the LLM

• Detects system prompt overrides, role injection, instruction hijacking, jailbreak attempts

• Detects data exfiltration URLs and encoded payloads

• Configurable action: log, strip, or block

• All detections logged as security events and sent via webhooks

Tool Aliasing

• Rename tools so the LLM sees cleaner names

• create_or_update_file → edit_github_file

• Aliases resolved transparently — downstream servers see original names

Tool Response Caching

• LRU cache for read-only tools (configurable patterns)

• Cache hits skip the downstream call entirely

• TTL-based expiration (5 minutes default)

• Automatic invalidation on cache overflow

Config Hot-Reload

• Edit spine.toml while Spine is running — changes apply in seconds

• Hot-reloadable: minifier level, rate limits, security policies, token budget, state guard patterns

• Non-reloadable (requires restart): server list, commands, audit DB path

• All reloads logged to the audit trail

Multi-User Audit

• Unique session ID generated per client connection

• Client name and version extracted from MCP handshake

• All audit entries tagged with session ID

• mcp-spine audit --sessions lists all client sessions

• mcp-spine audit --session <id> filters entries by session

Webhook Notifications

• POST alerts to Slack, Discord, or any JSON endpoint

• Triggers: security events, budget warnings, budget exceeded, tool blocked, rate limited

• Pre-formatted payloads for Slack blocks and Discord embeds

• Non-blocking (background threads)

Latency Monitoring

• Tracks response times per server (rolling window)

• Warns when average latency exceeds threshold (default 5s)

• Server latency panel in web dashboard with OK/SLOW status

Analytics Export

• mcp-spine export --format csv or --format json

• Filter by hours, event type

• Output to file or stdout for piping

Transport Support

• stdio — local subprocess servers (filesystem, GitHub, SQLite, etc.)

• SSE — legacy remote servers over HTTP/Server-Sent Events

• Streamable HTTP — MCP 2025-03-26 spec, single-endpoint bidirectional transport with session management

• All transports share the same security, routing, and audit pipeline

Web Dashboard

• Browser-based monitoring at localhost:8777

• Live stat cards: tool calls, security events, sessions, token budget, token savings

• Recent tool calls with server, session, and status

• Tool usage bar chart

• Server latency table with avg/max and OK/SLOW status

• Full request/response log with duration and token counts

• Security events and client sessions tables

• Auto-refresh every 3 seconds

• Zero dependencies (Python stdlib http.server)

Diagnostics

# Check your setup
mcp-spine doctor --config spine.toml

# Live TUI monitoring
mcp-spine dashboard

# Web dashboard
mcp-spine web --db spine_audit.db

# Usage analytics (includes token budget)
mcp-spine analytics --hours 24

# Export data
mcp-spine export --format csv --hours 168 --output weekly.csv

# Query audit log
mcp-spine audit --last 50
mcp-spine audit --security-only
mcp-spine audit --tool write_file
mcp-spine audit --sessions
mcp-spine audit --session <session-id>

Example Config

[spine]
log_level = "info"
audit_db = "spine_audit.db"

# Downstream servers — start concurrently
[[servers]]
name = "filesystem"
command = "npx"
args = ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/project"]
timeout_seconds = 120

[[servers]]
name = "github"
command = "npx"
args = ["-y", "@modelcontextprotocol/server-github"]
env = { GITHUB_TOKEN = "ghp_..." }
timeout_seconds = 180

[[servers]]
name = "sqlite"
command = "uvx"
args = ["mcp-server-sqlite", "--db-path", "/path/to/database.db"]
timeout_seconds = 60

[[servers]]
name = "memory"
command = "npx"
args = ["-y", "@modelcontextprotocol/server-memory"]
timeout_seconds = 60

[[servers]]
name = "brave-search"
command = "node"
args = ["/path/to/server-brave-search/dist/index.js"]
env = { BRAVE_API_KEY = "your_key" }
token_limit = 100000  # per-server daily budget
timeout_seconds = 60

# Remote server via Streamable HTTP (MCP 2025-03-26)
# [[servers]]
# name = "remote-api"
# transport = "streamable-http"
# url = "https://your-server.com/mcp"
# headers = { Authorization = "Bearer token" }

# Semantic routing
[routing]
max_tools = 15
rerank = true

# Schema minification — 61% token savings at level 2
[minifier]
level = 2

# Token budget
[token_budget]
daily_limit = 500000
warn_at = 0.8
action = "warn"

# Tool aliasing
[tool_aliases]
enabled = true
aliases = { "create_or_update_file" = "edit_github_file" }

# Tool response caching
[tool_cache]
enabled = true
cacheable_tools = ["read_file", "read_query", "list_directory"]
ttl_seconds = 300

# State guard
[state_guard]
enabled = true
watch_paths = ["/path/to/project"]

# Plugins
[plugins]
enabled = true
directory = "plugins"

# Webhooks
[webhooks]
enabled = true

[[webhooks.hooks]]
url = "https://hooks.slack.com/services/T.../B.../xxx"
events = ["security", "budget_warn"]
format = "slack"

# Human-in-the-loop
[[security.tools]]
pattern = "write_file"
action = "allow"
require_confirmation = true

[[security.tools]]
pattern = "write_query"
action = "allow"
require_confirmation = true

# Security
[security]
scrub_secrets_in_logs = true
audit_all_tool_calls = true
global_rate_limit = 120
per_tool_rate_limit = 60

[security.path]
allowed_roots = ["/path/to/project"]
denied_patterns = ["**/.env", "**/*.key", "**/*.pem"]

Security Model

Defense-in-depth — every layer assumes the others might fail.

Architecture

Client ◄──stdio──► MCP Spine ◄──stdio────────► Filesystem Server
                       │      ◄──stdio────────► GitHub Server
                       │      ◄──stdio────────► SQLite Server
                       │      ◄──stdio────────► Memory Server
                       │      ◄──stdio────────► Brave Search
                       │      ◄──SSE──────────► Legacy Remote
                       │      ◄──Streamable HTTP──► Modern Remote
                   ┌───┴───┐
                   │SecPol │  ← Rate limits, path jail, secret scrub
                   │Inject │  ← Prompt injection detection
                   │Router │  ← Semantic routing (local embeddings)
                   │Minify │  ← Schema compression (61% savings)
                   │Cache  │  ← Tool response caching (LRU + TTL)
                   │Guard  │  ← File state pinning (SHA-256)
                   │HITL   │  ← Human-in-the-loop confirmation
                   │Memory │  ← Tool output cache
                   │Budget │  ← Daily token tracking + limits
                   │Plugin │  ← Custom middleware hooks
                   │Audit  │  ← Session-tagged multi-user trail
                   │Hooks  │  ← Webhook notifications
                   └───────┘

Startup Sequence

1. Instant handshake (~2ms) — Responds to initialize immediately

2. Concurrent server startup — All servers connect in parallel via asyncio.gather

3. Progressive readiness — Tools available as soon as any server connects

4. Late server notification — tools/listChanged sent when slow servers finish

5. Background ML loading — Semantic router activates silently when model loads

Windows Support

Battle-tested on Windows with specific hardening for:

• MSIX sandbox paths for Claude Desktop config and logs

• npx.cmd resolution via shutil.which()

• Paths with spaces (C:\Users\John Doe\) and parentheses (C:\Program Files (x86)\)

• PureWindowsPath for cross-platform basename extraction

• Environment variable merging (config env extends, not replaces, system env)

• UTF-8 encoding without BOM

• Unbuffered stdout (-u flag) to prevent pipe hangs

Project Structure

mcp-spine/
├── pyproject.toml
├── spine/
│   ├── cli.py              # CLI: init, serve, verify, audit, dashboard, analytics, doctor, web, export
│   ├── config.py           # TOML config loader with validation
│   ├── proxy.py            # Core proxy event loop
│   ├── protocol.py         # JSON-RPC message handling
│   ├── transport.py        # Server pool, circuit breakers, concurrent startup
│   ├── audit.py            # Structured logging + SQLite audit trail + sessions
│   ├── router.py           # Semantic routing (ChromaDB + sentence-transformers)
│   ├── minifier.py         # Schema pruning (4 aggression levels)
│   ├── state_guard.py      # File watcher + SHA-256 manifest + pin injection
│   ├── memory.py           # Tool output cache (ring buffer + dedup + TTL)
│   ├── budget.py           # Token budget tracker (daily limits + persistence)
│   ├── plugins.py          # Plugin system (hooks, discovery, chaining)
│   ├── injection.py        # Prompt injection detection (8 pattern categories)
│   ├── tool_cache.py       # Tool response caching (LRU + TTL)
│   ├── webhooks.py         # Webhook notifications (Slack, Discord, JSON)
│   ├── dashboard.py        # Live TUI dashboard (Rich)
│   ├── web_dashboard.py    # Browser-based web dashboard
│   ├── sse_client.py       # SSE transport client (legacy)
│   ├── streamable_http.py  # Streamable HTTP transport (MCP 2025-03-26)
│   └── security/
│       ├── secrets.py      # Credential detection & scrubbing
│       ├── paths.py        # Path traversal jail
│       ├── validation.py   # JSON-RPC message validation
│       ├── commands.py     # Server spawn guards
│       ├── rate_limit.py   # Sliding window throttling
│       ├── integrity.py    # SHA-256 + HMAC fingerprints
│       ├── env.py          # Fail-closed env var resolution
│       └── policy.py       # Declarative security policies
├── tests/
│   ├── test_security.py
│   ├── test_config.py
│   ├── test_minifier.py
│   ├── test_state_guard.py
│   ├── test_proxy_features.py
│   ├── test_memory.py
│   ├── test_budget.py
│   └── test_plugins.py
├── examples/
│   └── slack_filter.py     # Example: Slack compliance filter plugin
├── configs/
│   └── example.spine.toml
└── .github/
    └── workflows/
        └── ci.yml

Tests

pytest tests/ -v

190+ tests. CI on Windows + Linux, Python 3.11/3.12/3.13.

License

MIT