Delimit MCP Server

Unify Claude Code, Codex, Cursor, and Gemini CLI with persistent context, governance, and multi-model debate.

API governance, persistent ledger, multi-model deliberation, security audit, and test verification — all shared across AI coding assistants.

Quick Install (10 seconds)

- uses: delimit-ai/delimit-action@v0

What Delimit Catches

Breaking Change Detected in Pull Request

+-------------+----------------------------------------+-----------------+
| Severity    | Change                                 | Location        |
+-------------+----------------------------------------+-----------------+
| HIGH        | Field removed: email                   | User schema     |
| HIGH        | Type changed: age (integer -> string)  | User.age        |
| HIGH        | Endpoint removed                       | GET /users/{id} |
+-------------+----------------------------------------+-----------------+

Why Delimit

APIs evolve, but your consumers depend on stability. One accidental breaking change can cascade into hours of debugging and frustrated users. Delimit catches these changes before they reach production.

---

Installation

GitHub Action (CI)

Add this workflow to .github/workflows/api-check.yml:

name: API Contract Check
on: pull_request

jobs:
  delimit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: delimit-ai/delimit-action@v0

Zero configuration required. Delimit auto-detects your OpenAPI specs.

No broken builds on day one -- Delimit never fails on existing issues, only new violations in pull requests.

CLI

npm install -g delimit-cli
delimit lint openapi.yaml

MCP Server (for AI Assistants)

Install from PyPI:

pip install delimit-mcp

Claude Code / Claude Desktop

Add to your MCP config (.mcp.json or Claude Desktop settings):

{
  "mcpServers": {
    "delimit": {
      "command": "delimit-mcp"
    }
  }
}

Cursor

Add to .cursor/mcp.json in your project root:

{
  "mcpServers": {
    "delimit": {
      "command": "delimit-mcp"
    }
  }
}

Codex CLI

Add to your MCP configuration:

{
  "mcpServers": {
    "delimit": {
      "command": "delimit-mcp"
    }
  }
}

The server communicates over stdio. No API keys or external services required.

---

MCP Tools

Tool	Description
delimit_lint	Diff + policy evaluation in one call. Returns pass/fail with violations.
delimit_diff	Structural diff between two OpenAPI specs. 23 change types detected.
delimit_policy	Evaluate changes against configurable rule sets.
delimit_impact	Business and technical impact assessment of detected changes.
delimit_ledger	Audit trail of governance decisions.

Example agent usage:

> delimit_lint(old_spec="api/v1.yaml", new_spec="api/v2.yaml")

{
  "passed": false,
  "violations": [
    {"type": "endpoint_removed", "severity": "error", "path": "GET /users/{id}"},
    {"type": "field_removed", "severity": "error", "path": "User.email"}
  ],
  "summary": "2 breaking changes detected"
}

---

Detected Breaking Changes

Delimit identifies 23 change types across these categories:

• Removed endpoints -- Endpoints that existed but are now gone
• Type changes -- Fields that changed type (string -> integer)
• Removed required fields -- Required response fields that were removed
• New required parameters -- Request parameters that became required
• Method removals -- HTTP methods removed from endpoints
• Schema changes -- Incompatible modifications to request/response schemas

The action automatically compares your PR API spec against the base branch.

What Happens on First Run

1. Auto-detection (2 seconds): Scans for OpenAPI/Swagger files
2. Baseline creation (3 seconds): Establishes current state without failing
3. Analysis (5 seconds): Compares changes and evaluates policies
4. Feedback: Posts clear, actionable comments on your PR

First run output:

Auto-detected: api/openapi.yaml
Baseline established
Running in advisory mode (non-blocking)

Supports

• OpenAPI 3.0, 3.1
• Swagger 2.0
• Multiple specs in monorepos
• JSON and YAML formats

Advanced Usage

Configure Detection

If auto-detection does not work for your setup:

- uses: delimit-ai/delimit-action@v1
  with:
    old_spec: api/v1/openapi.yaml
    new_spec: api/v2/openapi.yaml
    mode: enforce  # Fail CI on breaking changes

Custom Policies

Create .delimit/policies.yml to define custom governance rules:

rules:
  - id: no_endpoint_removal
    change_types: [endpoint_removed]
    severity: error
    message: "Endpoints cannot be removed without deprecation"

Policy Presets

Three built-in presets:

Preset	Behavior
strict	All detected changes are errors
default	Breaking changes are errors, others are warnings
relaxed	All changes are warnings only

delimit lint --policy strict openapi.yaml

Examples

Example	Description	Key Learning
breaking-change-demo	How Delimit catches breaking changes	Endpoint removal, field deletion
safe-change-demo	Backward-compatible changes	Adding fields, new endpoints
monorepo-demo	Multi-service API validation	Matrix builds, service isolation

Support

• Documentation
• Report Issues
• Discussions
• Website

License

MIT