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# WS-API: VariableServer
```ws://localhost:8888/api/ws/VariableServer```
## Purpose
JSON Variable Server
## Client to Server Command Messages
Add a Trick Variable to the current session.
```json
{ "cmd" : "var_add",
"var_name" : string
}
```
Stop sending periodic ```var_list``` messages (*see below*) from the server.
```json
{ "cmd" : "var_pause" }
```
Resume sending periodic ```var_list``` response messages from the server.
```json
{ "cmd" : "var_unpause" }
```
Send one ```var_list``` message from the server.
```json
{ "cmd" : "var_send" }
```
Clear all variables from the current session, that is: undo all of the ```var_add``` commands.
```json
{ "cmd" : "var_clear" }
```
Disconnect from the variable server.
```json
{ "cmd" : "var_exit" }
```
Set the period (in milliseconds) at which ```var_list``` messages are sent form the server.
```json
{ "cmd" : "var_cycle",
"period" : integer
}
```
Execute the given Python code in the host sim.
```json
{ "cmd" : "python",
"pycode" : string
}
```
Send the sie structure from the server. Response will be the ```sie``` response message (*below*).
```json
{ "cmd" : "sie" }
```
Send the units for the given variable. Response will be the ```units``` response message (*below*).
```json
{ "cmd" : "units",
"var_name" : string
}
```
## Server to Client Response Messages
Error Response
```json
{ "msg_type" : "error",
"error_text" : string
}
```
Periodic response containing the values of variables requested by ```var_add```.
```json
{ "msg_type" : "var_list"
"time" : double
"values" : []
}
```
Response to the ```sie``` command (*above*).
```json
{ "msg_type" : "sie",
"data" : string
}
```
Response to the ```units``` command (*above*).
```json
{ "msg_type" : "units",
"var_name" : string,
"data" : string
}
```
## Example Variable Server Client
```html
WS Experiments
```
Continue to [Extending the HTTP API](Extend-http-api)