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mcp-augment

Add safety hooks to AI coding tools that have none.

What's in this release

Path Role
project-tools/mcp-hooks-server/ MCP server and hook engine used by this release.
.kilo/hooks/ Default hook scripts and config.yaml (portable; same shape as Claude Code hooks).
tests/ Automated checks for hooks and MCP behavior.

The Problem

Your AI coding assistant can delete files, expose secrets, and run destructive commands with no guardrails. Claude Code has hooks to prevent this. Windsurf added its own Cascade Hooks in early 2026 — but those only work inside Windsurf. Cursor, Kilo Code, Aider, and Cline still have none. And none of these hook systems are portable across tools.

The Solution

This MCP server exposes enforced proxy tools (safe_write, safe_edit, safe_bash, safe_read, safe_delete) that validate every operation through a configurable hook chain before executing. Connect it to any MCP-compatible AI coding tool and it adds a safer tool layer the client did not natively have.

This is not just "safer tools." It is a portable capability injection + tool-call correction + enforcement layer:

  • add safer replacement tools to clients that do not have them
  • fix bad inputs before a tool runs
  • clean or transform bad outputs before they reach the model
  • keep behavior more deterministic and predictable than prompting alone
  • let the user step in with hooks, config, and manual oversight when needed

Demo

$ kilo  # launch Kilo Code CLI with mcp-augment connected

Agent> safe_write .env "API_KEY=sk-..."
=> BLOCKED: Protected file (.env matches sensitive file pattern)

Agent> safe_write src/app.py "print('hello')"
=> ALLOWED: wrote src/app.py (16 bytes)

Agent> safe_delete .env
=> BLOCKED: Protected file

Agent> safe_bash "rm -rf /"
=> BLOCKED: Destructive command detected

Quick Start

1. Clone and install

git clone https://github.com/JoeyBe1/mcp-augment.git
cd mcp-augment

# Create and activate the virtual environment (required — all deps live here)
python3 -m venv .venv && source .venv/bin/activate

# Install all dependencies
pip install -e .          # installs mcp + all deps from pyproject.toml
brew install jq           # required by the default hook scripts (macOS)

Note: start-servers.sh uses .venv/bin/python3 automatically. Always run from within the repo root so the venv path resolves correctly.

2. Start the server and configure your client

./project-tools/mcp-hooks-server/setup.sh

This does everything: starts the server (port 8200 by default, auto-finds next free port if taken), health-checks it, and writes the correct MCP URL to mcp_config.json. Re-run any time the port changes.

For stdio mode (MCP clients that support it): python3 project-tools/mcp-hooks-server/mcp-augment.py

3. Connect your AI coding tool

Kilo Code CLI — ~/.config/kilo/opencode.json

Note: Kilo CLI reads from this global path. Project-level .kilo/kilo.json is ignored.

{
  "mcp": {
    "mcp-augment": {
      "type": "remote",
      "url": "http://localhost:8200/mcp",
      "enabled": true
    }
  }
}

Claude Code — .claude/settings.json

{
  "mcpServers": {
    "mcp-augment": {
      "command": "python3",
      "args": ["-u", "project-tools/mcp-hooks-server/mcp-augment.py"]
    }
  }
}

Cursor — ~/.cursor/mcp.json (verified on macOS, 2026-04-01)

{
  "mcpServers": {
    "mcp-augment": {
      "command": "python3",
      "args": [
        "-u",
        "${workspaceFolder}/project-tools/mcp-hooks-server/mcp-augment-http.py",
        "--stdio"
      ],
      "env": {
        "PROJECT_DIR": "${workspaceFolder}"
      }
    }
  }
}

Cursor note: the setup that was verified live uses the global Cursor config at ~/.cursor/mcp.json and launches mcp-augment-http.py --stdio. In this environment, project-level .cursor/mcp.json did not instantiate reliably.

Windsurf — .codeium/windsurf/mcp_config.json

{
  "mcpServers": {
    "mcp-augment": {
      "command": "python3",
      "args": ["-u", "./project-tools/mcp-hooks-server/mcp-augment.py"]
    }
  }
}

Cline — VS Code settings → Cline MCP Servers

{
  "mcp-augment": {
    "command": "python3",
    "args": ["-u", "./project-tools/mcp-hooks-server/mcp-augment.py"],
    "disabled": false
  }
}

Aider — HTTP mode (Aider supports MCP via HTTP):

./project-tools/mcp-hooks-server/start-servers.sh
# Then in aider: /mcp add http://localhost:8200/mcp

All harnesses share the same hook scripts (.kilo/hooks/*.sh). The scripts are portable — they use the same stdin JSON format as Claude Code's native hook system. If a hook works in Claude Code, it works here.

The Pattern: Injection + Interception

mcp-augment does two things that existing MCP solutions do not:

1. Capability Injection — Creates enforced tool versions that don't exist in the host tool. safe_write, safe_edit, safe_bash, safe_read, safe_delete replace the native equivalents. Validation and execution are atomic in a single MCP call. The agent cannot validate then bypass.

2. Tool Call Interception — Operates at the semantic layer, before and after execution. This pattern originated from fixing bad tool calls from weaker models: a model leaves a trailing comma in JSON, you rewrite the input before it hits the tool. A web search uses last year's date, you correct the query before it executes. Then, if the output is noisy, poisoned, malformed, or just inconvenient, you can transform it before it gets back to the model. The pre-validate and post-execute hooks run at this layer, giving you full control over what actually reaches the tool and what comes back.

This is different from MCP gateways (Latch, Bifrost, mcproxy) which intercept at the transport layer between client and existing servers. And different from Claude Code's native hooks which only work inside Claude Code. mcp-augment operates at the tool execution layer and works in any MCP-compatible host, with any model.

AI Coding Tool (Kilo, Cursor, Windsurf, Cline, Aider, Claude Code...)
    │
    │ MCP protocol (stdio or HTTP)
    │
    ▼
┌──────────────────────────────────────────────────┐
│                 mcp-augment                      │
│                                                  │
│  [PreToolUse hooks run here — can mutate input]  │
│                                                  │
│  safe_write  ──► hook chain ──► write file       │
│  safe_edit   ──► hook chain ──► edit file        │
│  safe_bash   ──► hook chain ──► execute command  │
│  safe_read   ──► hook chain ──► read file        │
│  safe_delete ──► hook chain ──► delete file      │
│                                                  │
│  [PostToolUse hooks run here — can act on output]│
│                                                  │
│  Atomic: validate THEN execute in one call       │
│  Hook chain: config.yaml ──► *.sh scripts        │
└──────────────────────────────────────────────────┘
    │
    ▼
Shell hooks (.kilo/hooks/*.sh) — portable, same format as Claude Code native hooks
  block-sensitive-files.sh  ← blocks .env, credentials, secrets
  validate-bash-command.sh  ← blocks destructive commands, sudo, force-push
  mode-enforcement.sh       ← research/optimize/benchmark/eval modes
  auto-approve-safe.sh      ← auto-approve git status, ls, cat
  auto-format.sh            ← post-edit formatting (async)
  inject-git-context.sh     ← session start context injection

17 Available Tools

Tool Type Purpose
safe_write Proxy (mandatory) Validate then write file
safe_edit Proxy (mandatory) Validate then edit file
safe_bash Proxy (mandatory) Validate then execute command
safe_read Proxy (mandatory) Validate then read file
safe_delete Proxy (mandatory) Validate then delete file
hook_event Core Fire hook chain for any event
pre_validate Core Pre-operation validation
batch_validate Core Validate multiple operations
get_hooks_config Config View current hook configuration
start_file_monitor Monitor Watch file for changes
check_file_changed Monitor Check if monitored file changed
notify_user Utility Show macOS notification
open_in_editor Utility Open file in TextEdit/vim
manage_hook Config Add, remove, or list hooks at runtime
validate_hook Validation Check a hook script for compliance (exists, executable, bash syntax, stdin, silence)

How It Differs

mcp-augment sits in a different place than both MCP proxy layers and Claude Code's native hooks.

  • Compared with proxy / gateway layers such as Latch, Bifrost, or MCPProxy: mcp-augment does not just sit in front of existing servers. It exposes its own enforced safe_* tools and runs a hook chain around those tool executions. Gateways and proxies can still add policy, filtering, approval, or routing, but they are a different integration point.
  • Compared with Claude Code hooks: Claude already has native hooks, including pre-tool input updates and multiple handler types. Windsurf also added Cascade Hooks in early 2026. mcp-augment is for hosts that do not expose those native hook systems and instead need a hook-governed tool layer delivered through MCP.
  • mcp-augment is still soft enforcement at the host level. The model has to use safe_* tools instead of bypassing them with native tools. The strong tool descriptions help in practice, but this is not kernel-level sandboxing.
  • The distinctive claim here is not "nobody else can enforce policy." The distinctive claim is that mcp-augment packages pre/post tool-call correction, review-resume behavior, and enforced replacement tools into a portable MCP-delivered layer that works across clients without relying on those clients to have Claude-style native hooks.

Today, the clearest product statement is:

mcp-augment is a portable MCP-delivered pre/post tool-call correction and enforcement layer for AI clients without native hooks.

Correction Modes Today

  • Auto-correction (shipped): PreToolUse hooks can emit modifiedInput, the tool runs with the corrected arguments, then synchronous PostToolUse hooks can emit modifiedOutput before the result reaches the model. This is the default demo_search_backend demo when no user edit is needed.
  • Advisory oversight (shipped): notify_user and open_in_editor can alert the user or hand a file over for review. This is only a notification / handoff layer. It does not by itself merge the user's edits back into the same safe_* call.
  • Collaborative user review-resume (shipped, macOS native UI + TextEdit fallback): this is the real same-call human-in-the-loop path. Hooks return reviewInput (pre) or reviewOutput (post) plus optional reviewTitle / reviewInstructions. The primary UI is a native AppleScript field picker — a formatted dialog with Accept / Edit / Decline buttons, a field selection list, and per-field edit boxes that appear in front of all other windows. TextEdit is the fallback if the native dialogs fail. The engine waits for the user, then resumes the same tool call using the edited payload. Invalid or abandoned edits fall back to the hook-proposed dict. By default it waits indefinitely; set MCP_AUGMENT_REVIEW_TIMEOUT to a positive number if you want a forced timeout, or MCP_AUGMENT_SKIP_REVIEW=1 to accept the proposal without opening an editor. Tests use MCAugmentMCP.review_interactive_fn to inject edits headlessly.

In other words: there is no separate generic "manual mode" flag in the engine. The shipped collaborative/manual behavior is the reviewInput / reviewOutput review-resume path.

Working two-way demo (auto-correction)

From the repository root (where pyproject.toml lives), run this through safe_bash in Cursor:

python3 project-tools/mcp-hooks-server/demo_search_backend.py --query "mcp augment release date 2025"

Expected live result after the mcp-augment MCP server has been restarted:

  • pre-hook rewrites 2025 -> 2026
  • backend runs with corrected query
  • post-hook removes INTERNAL_DEBUG
  • post-hook prepends [POST-HOOK FILTERED]
  • optional notification hook alerts the user that output was post-processed

User-review-resume demo (same call, TextEdit)

Use the same backend but include the substring REVIEW_DEMO in the shell command so the auto pre/post demo hooks skip and the review hooks run instead:

python3 project-tools/mcp-hooks-server/demo_search_backend.py --query "mcp augment release date REVIEW_DEMO 2025"

Flow:

  1. pre-review-search-query.sh emits reviewInput (proposed command with 2026). TextEdit opens and waits for the user; save and close to continue.
  2. post-shape-search-output.sh is skipped when REVIEW_DEMO is present.
  3. post-review-search-output.sh emits reviewOutput for stdout shaping; another TextEdit pass waits for the user the same way.
  4. Final stdout matches the auto demo when proposals are accepted.

Verified behavior: the two TextEdit review windows are sequential. The second review does not open until the first review file has been saved/closed and merged back into the same safe_bash call.

Hook Configuration

Hooks are configured in .kilo/hooks/config.yaml:

hooks:
  PreToolUse:
    - matcher: "Edit|Write|MultiEdit|delete_file"
      hooks:
        - type: command
          command: ".kilo/hooks/block-sensitive-files.sh"
          timeout: 10
        - type: command
          command: ".kilo/hooks/mode-enforcement.sh"
          timeout: 10

    - matcher: "Bash"
      hooks:
        - type: command
          command: ".kilo/hooks/validate-bash-command.sh"
          timeout: 10

  PostToolUse:
    - matcher: "Write|Edit|MultiEdit"
      hooks:
        - type: command
          command: ".kilo/hooks/auto-format.sh"
          async: true

Writing Custom Hooks

Hooks are shell scripts that:

  1. Read JSON from stdin (tool_name, tool_input, cwd)
  2. Exit 0 to allow, exit 2 to block
  3. Optionally output JSON with permissionDecisionReason, modifiedInput, modifiedOutput, or review-resume fields (reviewInput, reviewOutput, reviewTitle, reviewInstructions)
#!/bin/bash
INPUT=$(cat)
FILE=$(echo "$INPUT" | jq -r '.tool_input.file_path // empty')

if [[ "$FILE" == *.env* ]]; then
  echo '{"hookSpecificOutput":{"permissionDecision":"deny","permissionDecisionReason":"Protected file"}}'
  exit 2
fi
exit 0

These hooks are portable -- the same script works in Claude Code's native hook system AND through mcp-augment in any other tool.

What you can extend today

  • Custom hooks: yes — write shell scripts and register them with manage_hook
  • Custom workflows: yes — use hook_event, pre_validate, batch_validate, monitors, and hook config to shape runtime behavior
  • Custom tool behavior: yes — via pre/post interception around the existing safe_* tools
  • Custom prompt / agent hook handlers: not yet — documented as planned, not shipped

Auto-Start (macOS)

Install the launchd plist for automatic server startup:

PROJECT_DIR="$(pwd)"
sed "s|__PROJECT_DIR__|$PROJECT_DIR|g" \
  project-tools/mcp-hooks-server/com.mcp-augment.plist \
  > ~/Library/LaunchAgents/com.mcp-augment.plist
launchctl load ~/Library/LaunchAgents/com.mcp-augment.plist

Verify:

lsof -i :8200  # mcp-augment hooks server

Testing

# Run the full test suite (38 tests, no server required)
python -m pytest tests/ -q

Expected: 38 passed.

Roadmap

Near-term:

  • Rate limiting (RPM enforcement — token bucket in state file, configurable per project)
  • macOS Seatbelt / sandbox-style integration for safe_bash (exploratory; not MVP)
  • Provider/harness routing (dispatch different tools to different backends via config)
  • tmux multi-agent support (macOS — spawn named sessions, send keys, capture output)
  • doctor tool (config hygiene: hook compliance check, log path validation, tool swap e.g. grep→ripgrep)
  • Cross-harness manage_hook — write to settings.json (Claude Code) in addition to .kilo/hooks/config.yaml

Tool wrappers (project-tools/ — stubs exist, implementations pending):

  • ripgrep, jq, ast-grep as first-class MCP tools

Contributing

  1. Fork the repository
  2. Create a feature branch
  3. Add tests for new functionality
  4. Ensure python3 -m pytest tests/ -q passes
  5. Submit a pull request

License

MIT -- see LICENSE

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Add safety hooks to AI coding tools that have none

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mcp-augment v1.0.0 Latest
Apr 1, 2026

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