MCP Rule Engine

An MCP server that captures code modifications, generates reusable rules, and injects them into AI agent context. Provides audit trail for every rule change.

Features

• Rule capture: Analyze code diffs via AST (Tree-sitter) and extract repeatable patterns as structured rules

• Deterministic matching: Language + file extension + tags + project ID retrieval, with weighted scoring (type/time decay/path match)

• Version audit: Every rule edit auto-creates a snapshot in RuleVersion table — query full history with getRuleVersions

• Batch workspace analysis: analyze_workspace tool diffs a git range or accepts fileContents directly (no git required)

• Session-level token budget: taskId-scoped <=2000 token tracking across multi-round query_rules calls

Related MCP server: standards-mcp

API

analyze_workspace

Analyze workspace changes and generate rule candidates. Accepts either a git commit range or direct file contents.

Inputs:

• baseCommit (string, required): Git base commit to diff against

• headCommit (string, optional): Git head commit (defaults to HEAD)

• paths (string[], optional): Filter to specific file paths

• fileContents (object[], optional): Direct content analysis — bypasses git

  • path (string): File path

  • originalContent (string, optional): Original content (omit if new file)

  • modifiedContent (string): Modified content

• taskId (string, optional): Session tracking ID for token budget isolation

query_rules

Query the most relevant rules for a given context.

Inputs:

• language (string, required): Programming language

• filePath (string, required): Current file path

• projectId (string, optional): Project scope filter

• tags (string[], optional): Tag-based filtering

• taskId (string, optional): Session tracking ID

Returns Top-K scored rules (<=2000 tokens total), with match reasons (language_match, path_match, content_match).

capture_diff

Analyze a single file diff and generate rule candidates.

Inputs:

• filePath (string, required)

• originalContent (string, required)

• modifiedContent (string, required)

• language (string, required)

• projectId (string, optional)

confirm_rule

Confirm, reject, edit, or skip a rule candidate.

Inputs:

• ruleId (string, required)

• action (enum: accept | reject | edit | skip, required)

• editedPattern (string, optional): New pattern when action=edit

• editedSuggestion (string, optional): New suggestion when action=edit

On edit, the server automatically snapshots the old content into RuleVersion before applying the update.

resolve_conflict

Resolve a conflict between two rules covering the same pattern.

Inputs:

• conflictId (string, required)

• resolution (enum: keep_a | keep_b | merge | skip, required)

• batchAllSession (boolean, optional): Apply same resolution to all conflicts this session

getRuleVersions

Query rule version history.

Inputs:

• ruleId (string, required)

Returns array of version snapshots, newest first.

list_rules

List rules with optional filters.

Inputs: All optional — language, scope (project|user|global), status (active|pending|archived), projectId, limit, offset.

Configuration

Codex CLI

codex mcp add mcp-rule-engine -- node D:/Desktop/mcp/dist/index.js

Or add to ~/.codex/config.toml:

[mcp_servers."mcp-rule-engine"]
command = "node"
args = ["D:/Desktop/mcp/dist/index.js"]
[mcp_servers."mcp-rule-engine".env]
DATABASE_URL = "file:D:/Desktop/mcp/prisma/data/rules.db"

VS Code

{
  "servers": {
    "mcp-rule-engine": {
      "command": "node",
      "args": ["D:/Desktop/mcp/dist/index.js"]
    }
  }
}

Cursor

{
  "mcpServers": {
    "mcp-rule-engine": {
      "command": "node",
      "args": ["D:/Desktop/mcp/dist/index.js"],
      "env": {
        "DATABASE_URL": "file:D:/Desktop/mcp/prisma/data/rules.db"
      }
    }
  }
}

Windows

When using node directly (as with this server), no cmd /c wrapping is needed. Ensure DATABASE_URL is an absolute path:

DATABASE_URL="file:D:/Desktop/mcp/prisma/data/rules.db"

Build

npm install
npx prisma db push    # Initialize SQLite database
npm run build          # Compile TypeScript
node dist/index.js     # Start server (stdio transport)

Tests

npm test                    # 45 unit tests
npm run test:e2e            # E2E integration test
npm run test:e2e -- --db ./tmp/test-rules.db  # Use file DB to avoid :memory: EPERM

Known Issues

• Prisma EPERM on Windows: Windows Defender may block schema-engine-windows.exe. Run: Add-MpPreference -ExclusionPath "...\\@prisma\\engines\\schema-engine-windows.exe"

• Codex --db :memory: EPERM: Sandboxed environments can't spawn cmd.exe. Use a file path instead.

• Codex 0.139.0 state DB: Abnormal exit may corrupt state_5.sqlite. Backup and remove to auto-rebuild.

License

MIT