GLOG is OSR in spirit, if not in name, and thus, abides by the tenants of OSR play:

Rulings Not Rules

The Referee is encouraged to come up with on-the spot rules for surprising actions, rather than by looking up a rule. Often the simplest solution is the right call.

Player Skill, not Character Abilities

In most cases, rolling the dice is the wrong call, it takes time, breaks up the narrative, and often reduces the fun. Remember that RPGs are about storytelling not luck, so if the story is better that the character succeeds, let them. Conversely, it’s not fun for a good idea to fail just because it’s not what the Referee expected. If a task is inherently risky, and failure is just as much (if different) fun as succeeding, provide a chance of the dice.

Heroic, but not Superhero

Characters are capable, but their not superheros. A knife in the gut will still kill them, and fighting is fraught, but these characters can overcome what the average person might not. Climbing stone walls or breaking down doors is within the wheelhouse of these characters.

No "Game Balance"

Many RPGs try to make every character equal to every other character, but this changes the game from one of player skill to one of system mastery. The person who knows the most rules and plans ahead will always win. In OSR, a fresh character can come across a dragon that will eat them in a single bite, in these cases being a smart player will win the day.

The Core Mechanic

Whenever the outcome of an action is uncertain, more often than not, you’ll be rolling 1d20 and succeeding on a result equal or lower than a Target Number. Rolling more than the Target Number means failure.

Throughout the text, the term "Roll Under" will be used. In these cases, equal is under. I probably should write "Under or Equal", but I’m lazy.

Players Always* Roll

In most cases, the player will roll for themselves. This means players roll to attack and roll to be attacked. The only time a player shouldn’t roll is if they wouldn’t know if they succeeded. This is often the case for discovering secrets, listening for things, or in social situations where nobody immediately reacts.

5 Margin Rule

When appropriate, the GM may allow a check to succeed if it’s margin of failure is less than 5. In these cases, the GM should offer a semi-related consequence in return. For example, a character misses a balance check by one, which would normally mean falling to their death, the GM may instead offer to simply alert nearby enemies, and allow the player to succeed anyway. The player may choose to take the success or not.

Opposed Roles

In the case where players are interacting with each other, the aggressor rolls, but the roll is modified by 10-(the relevant stat).

Ex. A character (with Attack 12) picks up a magical sword that commands them to attack their friend (with Defense 14). The character rolls against 8 (12+[10-14]).