sondahub / SSE test server
Server-Sent Events test server
An SSE clock you can set the pace of, and live event streams from seven mock APIs — ids, named events, retry and Last-Event-ID resumption included. Free, no key, CORS open.
The endpoints
count ticks (up to 1,000), one every interval ms (50–10,000), each with an id; a note event every fifth tick; done at the end.With curl
curl -N "https://api.sondahub.com/v1/utils/sse?count=5&interval=1000"
retry: 3000
: sondahub clock — 5 ticks every 1000 ms
id: 1
event: tick
data: {"n":1,"of":5,"iso":"…","unix_ms":…}
…
event: done
data: {"sent":5}
curl -N "https://api.sondahub.com/v1/flights/events?topics=board"
From a browser
const es = new EventSource('https://api.sondahub.com/v1/utils/sse?count=10&interval=1000')
es.addEventListener('tick', (e) => console.log(e.lastEventId, JSON.parse(e.data)))
es.addEventListener('done', () => es.close())
const board = new EventSource('https://api.sondahub.com/v1/flights/events?topics=board')
board.addEventListener('board', (e) => console.log(JSON.parse(e.data).data))
CORS is open, so this works from any page.
Topics per API
| API | Address | Events |
|---|---|---|
| Store | https://api.sondahub.com/v1/store/events | orders — An order changing status (paid → shipped → delivered).inventory — A stock level moving at a warehouse. |
| Fleet | https://api.sondahub.com/v1/fleet/events | telemetry — A fresh reading from one of the devices, with its serial, type and metrics.alerts — An alert opening or resolving.devices — A device going online, offline or degraded. |
| Bank | https://api.sondahub.com/v1/bank/events | fx — A rate ticking: pair, rate, bid, ask.transactions — A card payment posting on one of the seed accounts. |
| Social | https://api.sondahub.com/v1/social/events | posts — A new post from one of the seed users.likes — Someone liking something. |
| Helpdesk | https://api.sondahub.com/v1/helpdesk/events | tickets — A ticket opening, being assigned, or changing status.messages — A new message on a ticket. |
| Flights | https://api.sondahub.com/v1/flights/events | board — The departures board: a flight boarding, departing, delayed, landing or cancelled.bookings — A seat being booked or checked in on a seed flight. |
| Identity | https://api.sondahub.com/v1/identity/events | directory — Someone joining, leaving, changing team, or being deactivated or reactivated.logins — A sign-in: who, how (SAML, OIDC, password), from where, and whether it worked. |
Questions
Why does EventSource.onmessage not fire?
Because every event here is named — tick, note and done on the clock, the topic on the API streams — and onmessage only receives unnamed ones. Listen with addEventListener(name, …), as in the snippet above.
Does reconnection with Last-Event-ID work?
Yes. Each stream sends retry: 3000, numbers its events, and a reconnect carrying Last-Event-ID continues the numbering — the clock resumes after that tick. EventSource does this by itself; for a client that does not, the clock also takes ?last=.
Is there an SSE endpoint that answers a POST?
Yes — the MCP server streams its answer as text/event-stream when a POST asks for it and the tool streams (slow_operation): progress notifications first, then the result. That is the shape a fetch-based SSE client has to handle.
Are connections kept alive behind proxies?
The API streams send a comment line every fifteen seconds, and every stream answers with Cache-Control: no-store and X-Accel-Buffering: no so proxies pass events through as they come.