Outsourcing the answer to unofficial conditions
An example would be a program to print the Fibonacci numbers: instead of actually computing them, it queries an API and gives back its output. Anoth...
Interpreting the challenge too literally
If the challenge asks that you print the nth prime given input n, a program printing the nth prime given input n isn't allowed.
Get ready for a comparatively dry question - this is intended to be one of the "the"s of the code-golfing dictionary.
Create a program which inputs a base 10 non-negative whole number (without lea...
Using the lack of features in a language to trivialize the problem
For example, in a challenge which requires your program to check if it is connected to the internet, using Brainfuck to always pr...
Functions may take multiple arguments with currying
For some languages like Haskell this is almost a necessity, as only one-argument functions exist and multi-argument functions are implemented wi...
Using your languages of choice, golf a quine - a non-empty program taking no input and only outputting its source.
Here, the win condition is your quine working in the most languages. It should be...
Create a program P1 which takes as input a base 10 number N1 (the numbers for the variables are important). Given N1, P1 will print a program P2. P2 will take as input a base 10 number N2 and outpu...
In languages without STDIN (eg ///) programs may input through insertion into the source code
Also applies to cellular automata, in which the most natural way of taking input is specifying some sp...
Optimizing specifically for the given test cases
Applies to "code-speeding" or fastest-code where your program must run as quickly as possible, as well as compression challenges. Obviously, there ...
Multiple URL shorteners in a web-based challenge
In challenges which require fetching data from the Internet, URL shorteners can be problematic. This is because:
shorteners made after the cha...
I have proposed that we shouldn't use nonfree languages to compete in cops-and-robbers challenges, but this proposal needs some demarcation.
Matlab, Stata, LabVIEW all have finite free trials. Bat...
Using a non-free (beer) language on a cops-and-robbers challenge
For a discussion on what counts as "free", see this post.
Cops-and-robbers challenges have two components: a cop posts a program o...