Taming the Jenkins JSON API with Depth and "Tree"

Written by: Michael Neale
3 min read

Jenkins has a neat JSON api - which can expose or as much or as little as you want (and even do JSON-P to boot - for direct browser shenanigans). For the api purposes, you can think of Jenkins as a tree of interesting data.

You can control the "depth" of what the api returns when you do  GET on it -  depth tells it how deep to go. (?depth=X query parameter). So if you hit up your jenkins /api/json url - you can see everything down to a certain "depth". You can of course drill down - but if you have a lot of builds/jobs, then you can end up repeatedly loading data for each job - it is nice to get the data you want with one call of the api!

In one case I had, the difference between depth 2 and depth 3 was about 3MB of data *per request*. Ouch.

There is, however, a nicer way to control the data back - the "tree" query parameter - here you specify what elements and sub elements of a tree you want returned (nesting as needed) - this simple thing lets you craft a URL that specifies just the data you want back (at the cost of a horrendously long url that takes some time to tune) - this is also more efficient than filtering data as it was never generated and returned in the first place.

For example, https://yourjenkins/api/json?depth=2&pretty=true  will return something like:

Don't worry - I can't read it either. It is a bit of a "death ray" of data - let alone if you go deeper to get the data you want. If you are loading this into a client or browser this can hurt a lot.

However, the tree query parameter to the rescue (tweak the URL):


And you see something neat like this:

This is a lot more manageable (and in my case, exactly what I wanted and no more).

The whole point of this is to be explicit over what elements of the tree you want, and what fields.
In the above, I am saying I only want to know about "jobs", and the "name" and "lastBuild" fields etc. Of course - you can nest these structures - so you end up with an odd looking but powerful url that tells Jenkins to only return what you care about.

The pattern is tree=keyname[field1,field2,subkeyname[subfield1]] and so on.

Hit up your Jenkins /api to find out more.

Hope this saves you some time. 

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