Assert

MCP server for Assert — lets your AI coding agent generate, run, and inspect E2E tests without leaving the chat.

Describe a user flow in plain English. Assert generates a Playwright test, executes it in a real browser, and returns step-level results and failure screenshots — all from a single tool call in Cursor, Claude, Windsurf, or any MCP-compatible agent.

Sign up free at assert.click to get your API key and project ID before using this package.

What your agent can do

• Generate — describe a flow, get back a Markdown scenario ready to save and run
• Run — execute a saved scenario or ad-hoc Markdown against a real Chromium browser
• Inspect — fetch step-level pass/fail, error messages, and failure screenshot URLs
• List — browse saved scenarios visible to the API key

Requirements

• Node.js >=18.17
• A project-scoped Assert key — get one at assert.click

Setup

1. Create assert.config.json in your repo:

{
  "projectApiKey": "assert_project_key_here",
  "projectId": "project_123"
}

2. Add the MCP server to your agent config:

{
  "mcpServers": {
    "assert": {
      "command": "npx",
      "args": ["-y", "@assert-click/mcp"],
      "env": {
        "ASSERT_CONFIG": "/absolute/path/to/assert.config.json"
      }
    }
  }
}

That's it. Your agent now has access to all four Assert tools.

Private URLs

Targets such as localhost, 127.0.0.1, and LAN or VPN IP addresses are blocked by default.

Use a public URL unless the machine executing the Assert run is intentionally configured to allow private targets with:

ALLOW_PRIVATE_TARGETS=true

Set that on the machine or process running Assert. Do not put it in assert.config.json.

Environment variables

• ASSERT_API_KEY: API key (alternative to storing it in assert.config.json)
• ASSERT_PROJECT_ID: optional default project ID
• ASSERT_CONFIG: optional path to a config file or directory

Config files

The MCP server will look for these files from the current directory upward:

• assert.config.json
• assert.config.local.json

assert.config.local.json is merged on top of assert.config.json.

If you prefer env-based secrets instead of committing the key:

{
  "projectApiKeyEnv": "ASSERT_API_KEY",
  "projectId": "project_123"
}

Tools

assert_generate

Generate a Markdown scenario from a plain-English description.

Input:

• description: string — what the user should be able to do
• url: string — the starting URL
• project_id?: string
• save?: boolean — save to the project (default: false)

Returns:

{
  "scenario_id": "scenario_123",
  "markdown": "URL: https://example.com/login\nSCENARIO: Login\nPROCESS:\n  - Fill \"email\" with \"[email protected]\"\nEXPECT: Dashboard",
  "saved": true
}

assert_run

Execute a saved scenario or ad-hoc Markdown in a real browser.

Input:

• scenario_id?: string
• markdown?: string
• project_id?: string
• request_id?: string

Exactly one of scenario_id or markdown must be provided.

Returns:

{
  "run_id": "run_123",
  "status": "queued",
  "estimated_duration_seconds": null
}

assert_status

Fetch step-level results for a run.

Input:

• run_id: string

Returns:

{
  "run_id": "run_123",
  "status": "passed",
  "duration_ms": 4200,
  "steps": [
    {
      "description": "Fill email",
      "status": "passed",
      "error": null,
      "screenshot_url": null
    }
  ],
  "failure_summary": null,
  "full_log_url": null
}

assert_list

List saved scenarios visible to the API key.

Input:

• project_id?: string
• cursor?: string
• limit?: number

project_id is currently reserved for future filtering support. The current API lists all scenarios visible to the API key.

Returns:

{
  "scenarios": [
    {
      "id": "scenario_123",
      "name": "Login flow",
      "project_id": null,
      "last_run_status": "passed",
      "last_run_at": "2026-03-31T10:00:00.000Z",
      "url": "https://example.com/login"
    }
  ],
  "next_cursor": null
}

Errors

Errors are returned as structured JSON:

{
  "error": {
    "code": "INVALID_API_KEY",
    "message": "The ASSERT_API_KEY is invalid or missing.",
    "field": null
  }
}

Common codes:

• INVALID_API_KEY
• SCENARIO_NOT_FOUND
• RUN_NOT_FOUND
• VALIDATION_ERROR
• UPSTREAM_ERROR

License

MIT