Basel German is characterised by aspirates /kʰ, tʰ, pʰ/ which are absent or at least less common in other dialects.
Typically, words from Standard German or Latin are pronounced with aspirated /kʰ, pʰ, tʰ/, too, which is not or only to a lesser extent done in other dialects.
The pronunciation per se seems to derive from French (originally Parisian), and was probably re-interpreted as a lenis /x/ according to Basel German phonology.
Basel German also has more lenis sounds in word-initial position—for example, Dag ('day').
This lenition is now often absent due to influence from other dialects, for example, the name of Santa Claus, Santiglaus, is now often pronounced with /kʰ/ or /x/, as is the word Graft (Standard German Kraft), which traditionally has a lenis sound, now also /kʰ/ and /x/.
Fortis or long consonants in general are more stable than in other dialects—'to swim' is always schwimme, whereas it is pronounced with only a short /m/ in other dialects.
This is probably because in stressed words, short vowels only appear before double or geminated/long consonants.
Examples: schwimme ('to swim'), phagge ('to pack'), drugge ('to squeeze'), roott ('to guess' — note the long /oː/ followed by fortis /tt/) Unrounding was also typical, but now it has been abandoned by many speakers.
Lengthening always occurs before lenis (short) consonants, for example in words like Daag ('day'), loose ('listen'), miir ('we').
Typically (but not exclusively) open vowels occur before /r/; for example, Oor ('ear') has the allophone [ɔː], not [oː].
Examples: eläi ('alone'), draaie ('to turn'), drei ('three'), baue ('to build'), blaau ('blue'), vier ('four'), zue ('shut'), nöi ('new'); nei ('traditional').
There is a lot of confusion especially when it comes to the use of the grapheme ⟨y⟩, which is often used for rounded sounds, i.e. /ʏ/ or /y/, whereas it is exclusively used for /i/ traditionally.
Examples: drugge ('to push'), Läggerli (typical sweet cookie; but also Läckerli), Sagg ('bag'; but sometimes also Sack), Gugge ('bag', traditional word).
Obviously, especially the typical use of ⟨y⟩ and ⟨gg⟩ leads to confusion, even among native speakers, since the dialect is not taught in schools.