The Liddell Scott Jones dictionary is the most reliable source of information about Greek words, but it takes some effort to learn how to use it, especially the on-line version. The Perseus word study tool is very unreliable.
Here is a link to the page on which you can type in a Greek word using the Latin alphabet, following the conventions shown as to diacriticals:
http://www.perseus.tufts.edu/hopper/resolveform?redirect=true
You have to type everything exactly right, using the exact prescribed format for diacriticals, or you’ll get no response. Verbs must be in the first person singular present indicative active form, and nouns and adjectives in the nominative singular, and in the case of adjectives, masculine form. This can be very frustrating.
If you’re successful, you’ll get a choice among dictionaries–this is what you get when you search for ἀεί, entered as a)ei/:
http://www.perseus.tufts.edu/hopper/resolveform?type=exact&lookup=a)ei%2F&lang=greek
Then click on LSJ to see the LSJ entry:
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Da)ei%2F
There’s a list of various forms of the word in different dialects,. You want the standard Attic form, which is given in Item 2:
α_^ Att.
The line after the letter α indicates a long vowel and the French circumflex a short one. This means that the alpha can be either long or short in Attic.
The hard copy of the dictionary uses macrons and breves, but the on-line version uses _ for long vowels and ^ for short vowels, placed after the letter. If a vowel has a circumflex accent, there’s no need for _ because the vowel must be long.
For θύω (entered as qu/w), the situation is very complex:
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dqu%2Fw1
Some forms have a short υ; others a long:
[υ_ in fut. and aor., υ^ in pf. Act. and Pass., and aor. Pass.; υ_ generally in pres. and impf., exc. in trisyll. cases of part., …]
πράττω sends you to πράσσω, the older and more general form:
πράττω ,
A.v. πράσσω.
and in that entry you will find:
[α_ by nature, as is shown by the Ion. form πρήσσω, and by the accent in πρᾶγμα, πρᾶξις, etc.]
In the on-line version, you have to hunt for the information, but it’s there.