[4] "Ready or Not" has received positive reviews from music critics, praising the song's unique sound and Mendler's vocals, which have been compared to Cher Lloyd, Carly Rae Jepsen, and Demi Lovato.

The song was a commercial success in the United Kingdom, where it debuted in the top ten of the UK Singles Chart.

Mendler co-wrote the song with Emanuel Kiriakou, Evan Kidd Bogart and Andrew Goldstein.

[1] A Popdust review stated that "every detail is where it should be, from the multi-tracked vocals on the chorus to the synth sound effects that provide punctuation and punchlines to the verses, to some of the more clever rhymes in the lyrics—which include pairing "Oprah" with "Boca" and "I’m like a crook tonight" with "I could be your kryptonite."

The song consists of "layers of synths and backing vocals adding a musical and emotional intensity totally absent from the carefree verses.

Andrew Unterberger of Popdust was very positive with his review, saying that the song "is a playful, swinging and just impossibly catchy—the catchiest we’ve heard since our girl Carly Rae—pop number".

She praised her vocals, saying that "her sound is a mix between Carly Rae Jepsen and Demi Lovato" and described the music video as "super fun".

In its 11th week on Billboard Hot 100 the single jumped from position 94 to its peak of 49 selling 138,552 digital copies.

It also debuted at peaked number 17 on the New Zealand Singles Chart and number seven on the UK Singles Chart, selling 38,208 digital copies in its first week in the United Kingdom where it stayed in the top ten for four consecutive weeks and sold over 250,000 copies.

[citation needed] The music video was directed by Philip Andelman and it filmed at multiple locations in Los Angeles, California.

[12] The video starts with the camera showing Mendler's hands grabbing a box labelled "scavenger hunt".

[12] The music video starts with Mendler singing and hanging out with her friends at the top of Mulholland Drive.

Then some of her friends are seen in a skate park where a person is skateboarding and jumps over a guy who is lying upwards—another one of their scavenger hunts.