- In 3 Slytherin Marauders the Goblins inform Tom Riddle that he can't completely empty out Voldemort's Gringott's vaults... so he leaves him a single Knut. Also fugitives can seek asylum at Gringott's because "Gringott's customers are allowed to stay and count their gold for as long as they like."
- In The Adventures Of Harry Potter, the Video Game: Exploited when Harry discovers that his life is actually a videogame he determines he'll use every cheat, grind, and underhanded tactic available in order to exploit the system. Harry becomes a Munchkin and exploits such videogame tropes as Good Bad Bugs, Save Scumming, and Take Your Time.
- In Courage and Cunning Dobby gets around the Malfoy's orders forbidding him to identify who his Masters are by telling "Harry" that he just spent the evening getting rid of the red and gold hair dye (that "Harry" had earlier pranked Draco with) out of young master's hair.
- In The Dark Witch and the Necromancer Harry relates that when summoning demons one must be careful to watch the wording:
Demons tried to kill their summoners because they despised humans generally but even more the ones, who dared to force them under their will. Which demon wanted to serve a mere human? So they tried to interpret the commands of their master in such a way, that allowed them to hurt or even kill their caster. If the summoner wasn't careful enough, that would happen very quickly. The demons had to do whatever the summoner demanded, but if he didn't word his demand carefully, the demon would take revenge later. For instance, one of the inexperienced Necromancers in the past had summoned a Demon. He had worded his demand carefully but had forgotten to forbid the demon to bring anything with him. So he brought two things, a burning torch and a barrel full of black powder. He didn't hurt or kill his summoner directly, but as he swept down back to hell, he let both fall down to the ground and the Necromancer was... well... history.
- In Deadly Eyes of A Phoenix Reborn in the first task of the Tri-Wizard tournament Harry just summons the golden egg.
- In Harry Potter and the Acts of Betrayal Harry discovered from a document at Gringott's that many years ago Tom Marvolo Riddle swore a Fealty Oath to one Orion Mordecai Black but the way it was worded Riddle swore loyalty not to Orion but to "Lord Black" and as the current "Lord Black," Harry calls in the debt.
- In Harry Potter and the Descent Into Darkness when Harry faces allegations that he "cheated" during the first task of the Tri-Wizard Tournament by subduing the dragon using Paraseltongue Harry points out that nowhere in the rules did it say he had to fight the dragon.
- In Harry Potter and the Methods of Rationality, battles between the armies only end "when Professor Quirrell, in his personal judgment, decided one army had won by practical real-world standards":
There was no formal victory condition, Professor Quirrell had explained, because then Harry would figure out how to game the rules. Harry had to admit this was a fair cop.
- In the first match with an explicit rule, namely you're what ever faction you state you are, which means points are taken away from that stated faction if you are knocked (which allowed for spies and the massive Gambit Pileup that happened in that match), Harry joined forces with Draco's army, with both of them declaring themselves as part of Hermione's army, meaning she lost the massive lead in points.
- Given that the main character of Harry Potter and the Natural 20 is a huge Munchkin from an RPG Mechanics Verse, this is to be expected. One particular example is how he handled the problem of obtaining resources to make magic items (which require a sacrifice of expensive material): buying up massive quantities of table salt. A pound of salt is worth only a few cents in the modern world, but it's worth five gold in the world of Medieval Stasis.
- In Harry Potter and the Parseltongue Legend the Hogwarts rules state that students are only allowed to bring an owl, cat, or toad, or a bonded familiar. Since Harry already underwent the familiar bond ritual with his magical cobra he's allowed to keep his snake.
- In Harry Potter and the Power of Paranoia when developing a weapon to use against Voldemort, Luna develops a way to smuggle a large amount of plastic explosives past Harry's best wards by transfiguring them into wrackspurts. This bypasses the "transifugred animals" and "weapons" wards because the wards aren't equipped to handle something that doesn't technically exist.
- The premise of the one-shot Slash Fic I bid him! Harry makes use of the old medieval law of "Verbidden" (in which a criminal facing the gallows is released in exchange for marriage) to save good!Voldemort from execution and since the law was drafted in the middle ages and homosexuality was considered abnormal it was just assumed that it would always be a woman so no one specifically wrote the law so that it had to be a woman who bidded someone.
- In If Thems The Rules with help from Melania Black Harry exploits an obscure pureblood law to keep his powerful and influential stalker firmly in the friend zone.
- In Impossible Harry utilizes this after being forced to compete in the Tri-Wizard Tournament—he enters the arena with the dragon and instead of bothering the dragon or trying to get the golden egg he summons Quidditch Through The Ages and conjures himself a comfy chair and just sits there reading for twenty minutes:
Dumbledore: Mr. Potter. What, may I ask, are you doing?
Harry: I'm doing the task.
Dumbledore: But the task is to collect the egg from dragon.
Harry: No. To complete the task I would have to get the egg from dragon however just entering the arena constitutes competing which is enough to satisfy the contract.
- In Liquida Tenebris Harry gets Voldemort to vow on his life and magic to stop touching him. Voldie swears... and then immediately starts poking him with his wand.
- In Lord of Caer Azkaban Harry promises to remain at Hogwarts until he's completed his NEWTS... and then he hoodwinks Dumbledore into letting him take his NEWTS early.
- In The Mind's Guardian, an AU in which Harry has allied himself with Fudge against Dumbledore, as much as Fudge doesn't like Dumbledore he doesn't see any way to legally be rid of him but then Harry finds a loophole:
Harry: Isn't perjury grounds for impeachment?
You're referring to him claiming Voldemort's returned? Unfortunately, speeches before the Wizengamot and ICW are not sworn statements during a judicial proceeding. If he were anyone else, the Wizengamot might hold him in contempt, but that's all anyone can do.
Harry: I wasn't referring to his 1981 speech. I meant his testimony in the January 1982 trial of Severus Snape. Hogwarts doesn't have full transcripts, but The Daily Prophet printed an excerpt. I may be remembering this incorrectly, but I believe Dumbledore used the phrase 'Voldemort's death' during his testimony. If he's running around now saying he always knew Voldemort survived then he perjured himself during Snape's trial.
- From Oh God Not Again:
Dobby: Dobby wasn't trying to save the Great Harry Potter's life nor was he trying to send him away from Hogwarts. Dobby was trying to break Harry Potter's arm.
- In Passageways Harry's grandmother mentioned a demon which was ordered by the High Priest who summoned it to protect the pharaoh - but not his kingdom. The resulting devastation was what turned Egypt into a desert wasteland.
- In Past's Player Harry promises to stop Obfuscating Stupidity if Tom Riddle will just leave him alone. Tom agrees because Harry didn't specify how long he had to "leave him alone." Feeling generous he gives him a week...
- In Pavement Diaries Bellatrix manages to steal the prophecy orb that only Harry Potter and the Dark Lord can touch:
As for how she left with the orb, It was such a trivial loophole. So trivial, yet so brilliant. Bellatrix couldn't pick up the orb, but she could move the shelf it was on. So she did, and levitated it in a bag complete with featherlight and invisible extension charms, and walked right out the front door with it.
- In Princess of the Blacks Jennifer Black is able to bring her pet raven to Hogwarts despite it not being an owl because it's her bonded familiar.
- In Saving Her, Saving Us All, Sirius is restored to life because after being sent through the Veil of Death, it turns out to be a Veil of Judgment instead, and it judges Sirius' soul to be "pure," and thus refuses to condemn him. Harry is of course tremendously relieved, but then Harry remembers how Sirius almost got Snape killed with a schoolboy prank, so in chapter 3, Harry reluctantly asks Sirius why the Veil judged him to be pure in spite of that. Sirius answers that it was because he was so dumb as a schoolboy, he genuinely-within-his-heart didn't know that his prank could have killed Snape, so the prank didn't dilute his "purity" to the Veil of Judgment.
- In To The Waters and the Wild during flying lessons because Madam Hooch told them "no broomsticks in the air" Harry just flies after Draco without a broomstick.
- Averted in Visitor when Voldemort draws up an iron-clad secrecy contract to prevent Poppy from mentioning her treating Harry Potter or anything about their meeting to Dumbledore.
"It really was as loophole-free as he'd said it would be. It really was a perfect secrecy contract. If she had actually been planning to tell Dumbledore or anyone else anything, this would have made it impossible. Even the method of 'I'm lying to you but making it so obvious that you know I am lying' had been included in it. When she was finally through it all, twenty minutes had passed. Taking the quill she was being offered, she signed her name, and the contract shone bright silver before disappearing."
- Parodied in What A Cliché:
Harry: According to rule 149-A slash B-52 subsection alpha-3 beta rotgut of the Hogwarts Rulebook, I demand a resorting!
Harry: According to rule 721-D slash N-12 subsection beta-9 theta boogedy of the Hogwarts Rulebook, bonded partners of an enrolled student have the right to reside within the castle.
- What Would Slytherin Harry Do? is all about this trope. From using plausible deniability to beat Veritaserum to pointing out that the ban on clubs without Umbridge's permission only extend to regular meetings and their meetings were highly irregular.
- One ficlet has Harry getting around the ban on underage magic by getting a job. As he points out, the job requires traveling and irregular hours, making it impossible to say he wasn't working whenever he casts a spell.