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API OverviewΒΆ

Yamcs provides an HTTP API allowing external tools to integrate with Yamcs resources. Most HTTP endpoints send and expect JSON messages.


If you develop in Python consider using the Python Client which provides an idiomatic mapping for most of the operations documented here.

HTTP Verbs

The supported HTTP verbs are:


Retrieve a resource


Create a new resource


Update an existing resource


Delete a resource


All timestamps are returned as UTC and formatted according to ISO 8601. For example:

2015-08-26T08:08:40.724Z 2015-08-26

Error Handling

When an exception is caught while handling an HTTP request, the server provides feedback to the client by returning a generic exception message:

  "exception" : {
    "type": string, // Short message
    "msg": string // Long message

Clients should check on whether the status code is between 200 and 299, and if not, interpret the response with the above structure.


Cross-origin Resource Sharing (CORS) allows access to the Yamcs HTTP API from a remotely hosted web page. This is the HTML5 way of bypassing the self-origin policy typically enforced by browsers. With CORS, the browser will issue a preflight request to Yamcs to verify that it allows browser requests from the originating web page.

CORS is off by default on Yamcs Server, but available through configuration.

Response Filtering

Responses can be filtered using the query parameter fields, or alternatively by setting the HTTP header X-Yamcs-Fields. This is usually not needed, because when unspecified all fields are returned. Some clients may anyway want to be explicit, for optimizing the message sizes.

Field names are applicable to the top-level response message, and multiple fields can be separated by commas. Methods that return a list of messages apply the mask to each of the listed resources. Field paths can be of arbitrary depth separated by dots. Only the last part can refer to a repeated field.

Some examples:

Return information on the simulator instance, but include only the name and state fields:

curl 'localhost:8090/api/instances/simulator?fields=name,state'

Return a list of all instances, but include only the name and state fields:

curl 'localhost:8090/api/instances?fields=name,state'


All API methods are designed for JSON-over-HTTP. Matching type definitions in this documentation are written in TypeScript syntax because of its high readability. Note however that we do not currently mark parameters as optional (?).


As an alternative to JSON, most endpoints also support Google Protocol Buffers for a lighter footprint. To mark a request as Protobuf, set this HTTP header:

Content-Type: application/protobuf

If you also want to server to respond with Protobuf messages, add the Accept header:

Accept: application/protobuf

The proto files are available on GitHub. Using the protoc compiler, client code can be generated for Java, Python, C++ and more.

If the response status is not between 200 and 299, deserialize the response as of type yamcs.api.ExceptionMessage.