title: Which is more reliable for Github API Conditional Requests, ETag or Last-Modified?
body: <p>The <a href="https://developer.github.com/v3/#conditional-requests" rel="nofollow">Github API</a> specifies two headers that can be used in Conditional Requests, <code>Last-Modified</code> and <code>ETag</code>. Which is the more reliable when querying the API?</p>
  
  <p>For context: when using the api endpoint  <a href="https://developer.github.com/v3/git/trees/#get-a-tree" rel="nofollow"><code>GET /repos/:owner/:repo/git/trees/:sha</code></a> on each subdir of a large repo, every response contains the same <code>last-modified</code> value (even though the repo on github shows different authored dates) while the <code>etag</code> value for each is different. I'm wondering if the <code>ETag</code> is a more granular representation of repo content state change (for caching purposes).</p>