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Your LimeSurvey version: LimeSurvey Community Edition Verze 6.4.0+231218 
Own server or LimeSurvey hosting: Own server
Survey theme/template: Default
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Dear LimeSurvey users and developers,

our organization has plenty of surveys from which we need to fetch responses quite often. However, many of these are quite static in a sense that they don't change anymore (they are "waves" from longitudinal studies), so it's a waste of resources to download them again and again. I was thinking about some caching mechanism in our own proprietary API so a survey won’t download if it is not changed. The most "economic" way is the "get_summary" method, from which I can read if the number of responses changed. But that seems like not the most reliable source of the information desired.

What do you think about a new method that would return something like last-modified timestamp we know from HTTP requests? Or is there any better approach to this? All opinions are welcomed"

Many thanks,
Jan

Why not add an event in www.limesurvey.org/manual/AfterSurveyComplete where your ping your system to say "Hey there are a new answer" ?

Else : no Survey summary (or just id of the last response, or last response datetime etc  …)
But : you can create your own API function : gitlab.com/SondagesPro/RemoteControl/extendRemoteControl