Is there a website like OEIS for real constants?

Inverse symbolic calculator plus:

https://isc.carma.newcastle.edu.au/

There is also a tool RIES - Find Algebraic Equations, Given Their Solution with the source code available.

Wolfram|Alpha (https://www.wolframalpha.com) can return an assortment of information about a decimal number including a list of possible closed forms, e.g.

https://www.wolframalpha.com/input/?i=1.303577269034

https://isc.carma.newcastle.edu.au/ did not do anything useful with this particular number.