The song's musical style and production were inspired by synth-pop and new wave arrangements from the 1980s, and its lyrics chronicle a relationship in which two lovers have separated, but remain "cool" with each other as good friends.

"Cool" received generally positive reviews from music critics, being compared to Cyndi Lauper and Madonna songs from the 1980s.

The media have drawn parallels between the song's lyrical content and the romantic relationship that Stefani had with Tony Kanal, a fellow band member of No Doubt.

However, Austin felt reluctant to give the song to TLC after breaking up with group member Chilli and wrote "Damaged" for them instead.

The earlier song is about the heartbreak of the couple's seven-year relationship ending,[8] while "Cool" presents an amicable friendship between the pair, and explains that after the years that have passed and everything they have been through, they have reached a place where they are comfortable with each other and that they still remain very good friends.

[11] "Cool" opens with all five instruments, and as Stefani begins singing, the synthesizer is lowered, and the hard-hitting drum beat steadily increases in volume.

[10] The synthesizer emulates brass and woodwind instruments, while the bass and guitar retain a prominent and regular eighth note pulse, using a I–IV–V chord progression for the verses.

Music referred to the song as "a liltingly sweet paean to post-break-up friendships",[12] while Stephen Thomas Erlewine from AllMusic called it a "high school anthem-in-waiting" theme; it also was selected as one of the album's highlights.

[13] Richard Smirke from Playlouder commented that the song successfully used the same production formula as fellow album tracks "Serious" and "What You Waiting For?

[14] Jason Damas, in a review for PopMatters, characterized it as "a slippery slice of keyboard" New Wave song referring to it as a "pitched halfway between The Go-Go's and Cyndi Lauper".

[15] Eric Greenwood from Drawer B called "Cool" "a retrofitted [song] with stale synths and chugging guitars" with "dorkier lyrics than even Cyndi Lauper would dare".

[2] Entertainment Weekly reviewer David Browne described Stefani in "Cool", and in another song from the album ("The Real Thing"), as "a glacial '80s synthpop zombie".

[32] The accompanying music video for "Cool" was directed by longtime collaborator Sophie Muller and filmed in Lake Como, Italy in June 2005.

[34] The video follows the song's theme and depicts the relationship that Stefani has with a former boyfriend, who is played by Spanish actor Daniel González.

González and his new girlfriend, played by Tony Kanal's then-girlfriend and now-wife, Erin Lokitz, are shown walking up to a villa where Stefani answers the door.

The video for "Cool" premiered on MTV's top-ten chart program Total Request Live on June 30, 2005, where it reached number three.