- Gary the Snail
- SpongeBob SquarePants
- SpongeBob's tongue (debut)
- Squidward Tentacles
- Eugene H. Krabs
- Incidental 93
- Incidental 5
- Incidental 42
- Incidental 41
- Incidental 6
- Incidental 35
- Incidental 23
- Incidental 21
- Incidental 66
- Incidental 37B
- Incidental 36
- Incidental 65
- Incidental 14
- Incidental 30
- Incidental 45
- Incidental 64
- Incidental 70
- Incidental 48
- Incidental 31
- Incidental 71
- Incidental 47
- Incidental 22
- Incidental 67
- Incidental 3
- Incidental 91
- Incidental 40
- Incidental 49
- Incidental 60
- Incidental 9
- Bubble Bass (brown; cameo)
- Other Krusty Krab customers
- Sea urchins
- Patrick Star
- Mrs. Tentacles (debut; cameo)
- Sandy Cheeks (cameo)
The episode begins with SpongeBob waking up and realizing that it is April Fool's Day. Squidward sees him and wonders what SpongeBob is so pleased about, until he looks at the calendar, and realizes that it is April Fool's Day, which he says is SpongeBob's favorite holiday. Fearing the worst has to come, Squidward calls Mr. Krabs saying he caught something terrible and that he would not be able to make it to work. Mr. Krabs says that there is an art collector in his office who wants to buy Squidward's art and name him the artist of the month. So, Squidward immediately rushes to the Krusty Krab, only to find that it was a silly prank by SpongeBob and Mr. Krabs. Squidward attempts to resign from his job, but SpongeBob persuades him to stay, promising not to pull any further pranks on him.
However, SpongeBob continues to prank the customers inside the Krusty Krab while not pranking Squidward but getting carried away with it. The customers do not take offense to SpongeBob's pranks as they are harmless and playful in nature and they even laugh with SpongeBob. Although Squidward is not receiving any more tricks as SpongeBob promised, he gets furious over his and the customers' laughter. Eventually, an angry Squidward decides to get revenge on SpongeBob by showing him what he feels is a "real" prank.
Squidward sets an elaborate rope trap attached to an anchor suspended from the ceiling and squirts a blob of mustard in the middle of the lasso. As SpongeBob goes to clean it up, Squidward cuts the rope holding the heavy anchor, causing SpongeBob to get his foot caught in the rope, triggering a chain reaction that sends him flying around the restaurant, colliding into several objects and areas, ending with him into landing in a garbage can. Squidward laughs hysterically at him, but a hurt SpongeBob runs out of the restaurant crying. Bewildered by SpongeBob's reaction, Squidward calls out to him, saying that he was just kidding, and turns to the customers for support. But the customers are appalled by Squidward's prank, seeing it as far too harsh and nasty to be funny. They all feel sorry for SpongeBob and call Squidward out on this as they storm out of the restaurant in disgust. Distressed at their reaction, Squidward frantically insists that it was only a joke, but as he looks around at the damage his prank did to the restaurant, it slowly dawns on him that SpongeBob's pranks were actually funny, harmless, and meant to make people laugh so that SpongeBob could laugh with them, while his prank was just cruel, and meant to hurt and humiliate SpongeBob so he could laugh at him, all because he was not able to deal with it. Overcome with immense guilt, Squidward realizes that he has no choice but to apologize to SpongeBob.
Squidward goes to SpongeBob's house and sees SpongeBob's hat behind a rock. He goes over to apologize but then sees that it is just Patrick wearing the hat while digging. Squidward asks why he is wearing the hat and where SpongeBob is, and Patrick tells Squidward that SpongeBob is in the house "impressed" (instead of depressed) and was crying a lot. This, of course, makes Squidward feel even more guilty and he rushes over to SpongeBob's house and bangs on the door. He goes so far as to force his way in, but SpongeBob slides his arm through the door and removes the doorknob, clearly in no mood to talk to him. Losing patience, Squidward gets his clarinet and starts playing badly, refusing to stop until SpongeBob reluctantly answers him. Squidward attempts to apologize, but since apologizing to others is not something Squidward normally does, and because of his intense hatred toward SpongeBob, he initially finds himself to be physically incapable of doing so.
Squidward tries other methods of apologizing to SpongeBob, including sending him an apology note in a bottle but shoving the cork all the way in the bottle and apologizing to SpongeBob far away via two cans attached to a string, but these are foiled by SpongeBob not having a bottle opener and Patrick using the string as floss, respectively. Eventually, he is able to apologize by putting a bubble over his head, so that SpongeBob does not actually hear his apology. Squidward walks away, saying that his conscience is clear, but is confronted by memories of what he did. After he imagines his mother telling him he stinks, he runs back and genuinely apologizes to SpongeBob, even admitting he likes him, his friends, and everyone else in Bikini Bottom, but tells SpongeBob not to tell anyone. SpongeBob promises not to tell and forgives him, but then fully opens his front door, revealing that everyone else is inside behind him, and witnessed Squidward's apology. They all say "April Fools!" to Squidward, who is flabbergasted by this. Squidward states that he was fooling them as well before running away to his house, while laughing maniacally, causing SpongeBob to ask, "What would we do without Squidward?", ending the episode.
- SpongeBob pulling pranks on people.
- Squidward gets more irritated by SpongeBob's pranks despite not being pranked himself.
|( ‣ ) Production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
• 12th Street Rag - Sage Guyton, Jeremy Wakefield [title card]
‣ Aloha - Dick Stephen Walter [Opening]
‣ Courting Clarinets - Stefan Maciejewski ["We're gonna become peasants!"]
‣ Me for You - George Callert [Huge pitcher of lemonade/SpongeBob laughing]
‣ Dramatic Impact (3) - Ivor Slaney [Shot of calendar]
‣ Captain Lenoe's - Michael Arthur, Colin Cater, Mick Graves, The Folk Players, Sarah Graves, Simon Ritchie [Squidward calls Mr. Krabs]
‣ Airs and Graces (b) - Paddy Kingsland ["I have arrived."]
‣ The Tip Top Polka/The Cliff Polka - Chelmsford Folk Band [SpongeBob and Krabs laughing]
‣ Blue Blood F - Gregor F. Narholz ["Squidward, wait!"]
• 12th Street Rag - Sage Guyton, Jeremy Wakefield [SpongeBob playing pranks on people]
‣ Heavy Footsteps (a) - Paddy Kingsland [Squidward setting a trap]
‣ Shock (u) - Dave Hewson [Anchor falls]
‣ On with the Race - Dennis Farnon [Rope sends SpongeBob flying everywhere]
‣ Pua Paoakalani B - Kapono Beamer, Queen Lili'uokalani ["April Fools, you little sausage!"]
‣ Royal Hawaiian Hula - Kapono Beamer [Patrick digging]
‣ Fates [#62.02] - Gregor F. Narholz ["SpongeBob, let me in there!"]
• Clarinet - Brad Carow [Squidward playing clarinet]
‣ Hawaiian Cocktail - Richard Myhill [Squidward trying to apologize]
• Seaweed 2 - Steve Belfer [message in a bottle]
‣ Killer Birds - Gregor F. Narholz [Squidward remembering what others said]
‣ Paradise Isle - George de Fretes, Jan Rap [Squidward apologizes]
‣ Nostalgic Hawaii - George de Fretes, Jan Rap [Ending]
- This episode is available on the SpongeBob Goes Prehistoric, Complete 1st Season, SpongeBob SquarePants Vol. 2, Nickelodeon Fool Proof Fun, The First & Second Seasons, The Adventures Of Waterman & Supervisor!, The SpongeBob SquarePants Collection, From the Beginning, Part 1, Nicktoons: Laugh-a-Minute DVD, Big Hits: Volume 2, Triple Pack 4, The Ultimate SpongeBob Box Set, The SpongeBob SquarePants 8 Season DVD Collection, Your Shoe's Untied, Favorite Episodes, Exposed!: The Ultimate Box Set, Home Sweet Pineapple (Polish only), The Ultimate Box Set, The Complete First Season, Movies & TV Collection, The Best 200 Episodes Ever, First 100 Episodes, and Fools in April DVDs VideoNow.
- This episode is also available on the SpongeBob Goes Prehistoric and Nicktoons: Laugh-a-Minute VHS tapes.
- "Fools in April" was ranked #84 during the Best Day Ever event from November 9–10, 2006.
- The episode was originally titled as "April Fools."
- This is the first episode to use "12th Street Rag" for title card music.
- This marks the first usage of the APM tracks "Pua Paoakalani (b)," "Paradise Isle," and "Dramatic Impact (3)."
- This is Bubble Bass' final appearance in the series until 11 years later. He would later return in "Plankton's Good Eye" and would stay on the series as a recurring character since then.
- However, his skin tone in this episode is mauve rather than olive green. This is the only time he appears this way.
- The line "You stink!" is a recycled quote from "Pickles."
- Before the beginning of 2020, Nickelodeon USA originally broadcast this episode and "Neptune's Spatula" on April 1 only, making both episodes extremely rare to find on TV. The network has started to broadcast both episodes outside of April, though less often than most other episodes.
- The same was also true for "Valentine's Day" and "The Paper." Nickelodeon originally ran both episodes on Valentine's Day only, since the former is a Valentine's Day episode. The network also started to broadcast both episodes on occasion outside February.
- Nickelodeon USA continues to only broadcast "Scaredy Pants," "I Was a Teenage Gary" and "The Legend of Boo-Kini Bottom" in October, as they are all Halloween episodes.
- Nickelodeon USA continues to only broadcast "Christmas Who?" and "It's a SpongeBob Christmas!" in December, as they are both Christmas episodes.
- Nickelodeon, SpongeBob's home channel was created on April 1, 1979; thus making this episode air during the channel's 21st anniversary.
- In real life, if SpongeBob had given Gary salted shells, he would have died as salt is dangerous for sea snails.
- This could be another reason why Gary was crying in that scene.
- In the Polish dub, the episode's title is "Prima Aprilis," which translates to "April Fools."
- On the old Nickelodeon website, this episode is alternatively known as "April Fools."
- On the April 1, 2013 airing when Squidward says, "I was just kidding," it was interrupted by Nick Studio 10 which ran from March to mid-June for 30 seconds by showing a walrus roaring and cuts back when Squidward saying, "It was just a joke."
- This interruption also happened in several other SpongeBob SquarePants, The Fairly OddParents, and Monsters vs. Aliens episodes.
- This was Sandy's last appearance in season 1 and traditional cel animation before her ten-month hiatus until her return in "Wormy" in season 2.
- Coincidentally, both episodes use "12th Street Rag" as title card music.
- Innuendo: When Squidward is struggling to apologize to SpongeBob, his head briefly turns into a donkey's head and brays, which implies that Squidward is a "jack-a**." This happens again in "Christmas Who?."
- During the Best Day Ever marathon, this episode was paired with "Krusty Love."
- Plankton is the only main character to not appear in this episode.
- When Squidward looks at the calendar, his mouth does not sync with what he is saying.
- After being pranked the first time, Squidward places his hat on Mr. Krabs' desk, but he has it in his hand when he leaves Mr. Krabs' room.
- During the scene of Squidward's prank, Incidental 71 is naked and everyone except for Squidward is poorly drawn. However, when he says "April Fools, jerk," he is better drawn and is wearing a purple shirt and shorts.
- When Squidward's head explodes while apologizing, neither his house nor Patrick's house is there anymore.
- When Squidward gives SpongeBob a message in a bottle, he puts a cork in it, which disappears as it rolls towards SpongeBob.
- When Squidward sees Patrick, the hat is down to Patrick's eyebrows. However, when Squidward says, "Why are you wearing that hat?!" the hat is farther up Patrick's forehead.
- When SpongeBob and the others say "April Fools!" to Squidward, SpongeBob's mouth does not move.
- Squidward's April Fools prank propels SpongeBob with an anchor. However, when the anchor drops, SpongeBob flies like usual, but the anchor is gone completely. Also when the anchor drops, the rope is tied to both of SpongeBob's legs, but through the rest, it is tied to one of his legs.
- When the fish leave the Krusty Krab, multiple far-distance fish clone simultaneously.
- When SpongeBob tells Gary that they are moving, Gary has an eyelash that vanishes in the next shot.
- The first time Squidward tries to apologize to SpongeBob, when he blinks, his eyelids turn to the teal color they would become in season 2 rather than the seafoam they are for this season.
- When SpongeBob pranks Incidental 41, his right tooth turns yellow for a split second.
- When SpongeBob passes through Bubble Bass' rear, his shirt is white and his shorts are dark blue, but when Squidward sees the injury afterward, his shirt is light green and his shorts are purple.
- When SpongeBob is taken around the bar, there is a frame with his mouth missing.
- When SpongeBob says "What?!," his house's doorknob is missing as it should be; in the next shot, it appears.
- Even after SpongeBob reveals to the old lady his prank of giving her a spoon rather than a fork, she still walks away with the spoon.
- When Squidward imagines the fish telling him, "April Fools, jerk," Incidental 6 was shown in the illusion; earlier, Incidental 71 told him this.
- While Squidward is running through the restaurant to "catch" SpongeBob, the same characters can be seen over and over again, as if he was running in a circle, but is actually running in a straight line.
- When SpongeBob and the others say "April Fools!," to Squidward, Sandy's head and eyes duplicate themselves.