Mercure: Real-time Made Easy
Mercure streams real-time updates from your servers to any client. It is a fast, reliable, battery-efficient replacement for WebSockets and every library, framework, or hosted service built on top of them.
Mercure shines when you need to stream LLM tokens, agent steps, or any other server-driven update to your users. It relies on SSE, the same transport behind streaming responses in ChatGPT, Claude, and the OpenAI/Anthropic APIs. The same simple building block also adds streaming and asynchronous capabilities to REST and GraphQL APIs, mobile apps, and IoT devices.
Mercure is free and open source. For production deployments, we run two managed editions on top of the same code:
Mercure: at a glance
Stream LLM tokens, AI agent steps, and tool-call updates
Cloud-native: official Docker image and Helm chart on Artifact Hub
Built on Caddy: automatic HTTPS, HTTP/2 and HTTP/3, zstd compression
Fully configurable through a REST API and structured config files
Official real-time solution for Symfony and Symfony UX
Native browser support, no client-side SDK
Publish with a single authenticated POST request
Subscribe via Server-Sent Events over plain HTTP
Private updates with JWT authorization and topic selectors
Automatic reconnection with Last-Event-ID replay and state reconciliation
Built-in event store for event sourcing
Presence API and subscription events
Production observability: Prometheus and OpenMetrics endpoints, structured JSON logs, OpenTelemetry-ready via Caddy
Drop-in for REST and GraphQL APIs
Works with any backend: Node.js, PHP, Python, Go, serverless
Optional end-to-end encryption with JWE
Open IETF-style protocol with multiple independent implementations
Privacy by design
Built for regulated industries and sovereign workloads. Mercure Cloud runs in the EU under French jurisdiction; the open source Hub and Mercure Enterprise can be self-hosted on your own infrastructure for full data control.
Mercure Cloud, hosted in Europe
EU-only data residency: production runs in Amsterdam on European infrastructure, operated by a French SAS under GDPR and CNIL oversight.
Self-host for full control
The MIT-licensed Hub and Mercure Enterprise run anywhere, including air-gapped and sovereign clouds. Bring your own keys, your own region, your own compliance scope.
Modern encryption out of the box
State-of-the-art TLS via Caddy with automatic certificate management, HTTP/2 and HTTP/3 by default, plus optional end-to-end encryption with JWE and JWT-authorized topic selectors.
Hardened by default
Rootless-compatible Docker images, hardened Helm chart with NetworkPolicies and pod security, automated vulnerability scanning and dependency review on every commit.
They use Mercure
Plus government agencies, banks, healthcare systems, SaaS leaders, retailers and media groups across Europe, the Americas and Asia. Some run the open source Hub on their own infrastructure; others use Mercure Cloud or Mercure Enterprise.
Need help?
Documentation
Start with the docs to discover what Mercure can do.
Community support
Chat with the community on Slack and Stack Overflow.
Training
Level up your Mercure skills with our hands-on training.
Professional services
Les-Tilleuls.coop offers web development, training, and consulting around Mercure.