Framework plugin support mentioned as a potential contribution target, allowing integration of sncro debugging capabilities into Django applications.
Framework plugin support mentioned as a potential contribution target, allowing integration of sncro debugging capabilities into Express.js applications.
Provides drop-in middleware for FastAPI applications, enabling sncro debugging capabilities with browser inspection and DOM interaction tools.
Provides drop-in middleware for Flask applications, enabling sncro debugging capabilities with browser inspection and DOM interaction tools.
Framework plugin support mentioned as a potential contribution target, allowing integration of sncro debugging capabilities into ASP.NET applications.
Framework plugin support mentioned as a potential contribution target, allowing integration of sncro debugging capabilities into Next.js applications.
Open-source components of sncro — the MCP relay, the browser-side agent, and the framework plugins that let AI coding assistants inspect a live browser.
Path | What |
| FastAPI app that exposes an MCP server plus long-poll endpoints for agent.js |
| Browser-side script injected by the middleware; pushes console + DOM data to the relay |
| FastAPI / Starlette plugin — drop-in middleware for FastAPI apps |
| Flask plugin — drop-in middleware for Flask apps |
|
|
Related MCP server: agnt
┌──────────────┐ MCP ┌──────────┐ long-poll ┌─────────────┐
│ Claude Code │──tools────▶│ relay │◀──────────────│ agent.js │
│ (or other │ │ (relay/) │ snapshots │ (injected │
│ MCP client) │◀──results──│ │──────────────▶│ by plugin) │
└──────────────┘ └──────────┘ └─────────────┘
▲
│ same-origin
│ cookies
┌─────────────┐
│ your app │
│ (plugin is │
│ installed) │
└─────────────┘Claude calls create_session (MCP tool) → relay returns a 9-digit session key + URL
User visits the URL in the browser where their app is running → confirms via "Allow sncro debugging?"
The plugin drops a cookie, agent.js is injected into subsequent HTML responses on that origin
agent.js pushes baseline data (console, errors) and long-polls for on-demand queries (query_element, get_page_snapshot, etc.)
Most users don't need to run the relay yourself — the hosted version at relay.sncro.net is free-tier friendly. Register your project at sncro.net and grab your project key.
FastAPI: drop middleware/sncro_middleware.py into your project, then:
from middleware.sncro_middleware import SncroMiddleware, sncro_routes
app = FastAPI(debug=True) # sncro only loads when debug=True
if app.debug:
app.include_router(sncro_routes)
app.add_middleware(SncroMiddleware, relay_url="https://relay.sncro.net")Flask: drop middleware/sncro_flask.py into your project, then:
from sncro_flask import init_sncro
app = Flask(__name__)
if app.debug:
init_sncro(app, relay_url="https://relay.sncro.net")Both middlewares only activate in debug mode — zero overhead in production.
We love new framework plugins. CONTRIBUTING.md has the full spec for what a plugin must do — cookies, routes, security headers — plus the test template. Django, Rails, Express, Next.js, ASP.NET, Go — all welcome.
Bug reports and security issues: see SECURITY.md.
MIT. See LICENSE.
The dashboard at sncro.net (project management, billing, admin) lives in a separate proprietary repo.
This server cannot be deployed
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