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# WebSocket Data Format
TimePlot's WebSocket source accepts UTF-8 text frames whose contents can be parsed into one of the supported payload shapes below.
## Recommended payload
Send one JSON object per message:
```json
{
"timestampMs": 1250,
"value": 0.482
}
```
Fields:
- `value` — required numeric sample value
- `timestampMs` — optional numeric source timestamp in milliseconds
If `timestampMs` is present, TimePlot uses it to preserve the source timing relationship and aligns it onto the app's plot timebase.
If `timestampMs` is omitted, TimePlot stamps the sample at the current plot time when the message arrives.
## Other accepted object keys
TimePlot also accepts these alternate numeric field names:
- value fields: `value`, `y`, `signal`, `data`
- time fields: `timeMs`, `timestampMs`, `timestamp`, `t`
Examples:
```json
{"y": 0.91, "t": 2040}
```
```json
{"signal": -0.13, "timestamp": 9810}
```
## Arrays
A single message may contain an array of supported payloads:
```json
[
{"timestampMs": 1000, "value": 0.2},
{"timestampMs": 1100, "value": 0.3},
{"timestampMs": 1200, "value": 0.5}
]
```
This is useful for batching.
## Bare numeric messages
These also work, though JSON objects are preferred:
```text
0.418
```
or:
```json
42.5
```
These are treated as samples without an explicit timestamp.
## Unsupported / ignored messages
Messages are ignored if TimePlot cannot find a numeric sample value.
Examples of ignored payloads:
- empty strings
- non-numeric strings
- JSON objects without a numeric `value`-like field
## Demo server compatibility
The included demo server sends messages like:
```json
{
"timestampMs": 1870,
"value": 0.735812,
"sequence": 19,
"profile": "telemetry"
}
```
Extra fields are safe. TimePlot ignores anything it does not need.
## Running the demo server
```bash
bun run ws:demo
```
Environment options:
- `PORT` — default `8080`
- `TIMEPLOT_PROFILE` — `telemetry`, `chirp`, `steps`, or `burst`
- `TIMEPLOT_INTERVAL_MS` — message interval in milliseconds
Example:
```bash
PORT=8090 TIMEPLOT_PROFILE=chirp TIMEPLOT_INTERVAL_MS=50 bun run ws:demo
```
Then set a signal source type to `WebSocket` and point it at:
```text
ws://localhost:8090
```
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