Instead of doing the hard work to separately specify the search term (`q=oracle`) and tag (`tagged=blockchain`), just put whatever you put in the search box on the site (`oracle [blockchain]`) in the `q` parameter itself. [This API call][1] gives 66 results, just like the site search:

[![enter image description here](https://i.sstatic.net/GK4oY.png)](https://i.sstatic.net/GK4oY.png)

[1]: https://api.stackexchange.com/docs/excerpt-search#order=desc&sort=activity&q=oracle%20%5Bblockchain%5D&filter=!9_bDE.BDp&site=stackoverflow&run=true