Diagram of the Mercure protocol: a publisher pushes updates through the Hub to subscribed browsers and HTTP clients via Server-Sent Events

Open source · MIT licensed

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:

Get startedSelf-host the open source Hub

Production-ready editionsMercure Cloud Mercure Enterprise

Cloud hosted in the EU (Amsterdam, France-based SAS). Open source and Enterprise editions are self-hostable for full data control.Built on an open IETF-style specification. Read the spec.

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.

See all references

Need help?

Documentation

Start with the docs to discover what Mercure can do.

Read the docs

Community support

Chat with the community on Slack and Stack Overflow.

Slack Stack Overflow

Training

Level up your Mercure skills with our hands-on training.

Get trained

Professional services

Les-Tilleuls.coop offers web development, training, and consulting around Mercure.

Les-Tilleuls.coop