Estimating GURPS Skill Levels

GURPS is a skill-based roleplaying game. If you understand how skill levels work mechanically, you can run or play a game. It’s easy to lose sight of the skill system because GURPS has elaborate options for character customization. But, if you’re feeling overwhelmed, you can always strip the system back to skills in order to create a manageable gaming experience.

The GURPS Skill Triangle

In play, GURPS skills are driven by three factors: the base skill level, the effective skill level, and the task difficulty modifiers. These three elements make up what I call the GURPS Skill Triangle. If you understand how the Triangle is put together, you can easily improvise challenges in GURPS.

Base Skill Level

The base skill level is what level the character has listed for a skill on their character sheet. The Basic Set gives the following descriptions for what base skill levels represent (paraphrasing from p. B172):

  • Ordinary folks have base skill levels ranging from 8 to 13. Skills important to the character’s profession tend to be at level 12 or 13; rarely used skills are often at level 8 or 9.
  • Experts have skill levels that go higher. In general, even a master in the field will usually max out a specific skill at 20 or 25, preferring to study complimentary skills instead of pushing an elite skill above level 25.

Base skill levels below 10 are poorly known skills; the character can succeed at the task on occasion or with aid, but frequently struggles with the ability. At skill levels 10 or 11, the character is more often successful but their abilities are still inconsistent. At level 12, skills are solid enough to cover most occupational demands (whether that be swinging a sword, negotiating a settlement, or navigating a bureaucracy). And, at levels 14 and above, the person demonstrates mastery of their ability.

Task Difficulty Modifiers

Of course, some tasks are more difficult than others. The second leg of the Triangle, task difficulty modifiers, is a catch-all for the situational modifiers that apply to a given success roll. This can include bonuses for using complimentary skills or easier-than-average conditions, penalties for poor equipment or working at a different tech level—anything that changes the odds of success. GURPS has rules that codify the modifiers for a variety of situations, but GMs can also use generic task difficulty modifiers to indicate that a task is more or less challenging.

The default task difficulty, +0, represents using the skill under normal adventuring conditions. Ordinary, everyday situations are less stressful and therefore get bonuses to reflect the less challenging circumstances. By contrast, tasks that would give pause to even brave adventurers receive task difficulty penalties in order to reflect the challenge of the situation.

Basic Set pp. B345–B346 describes the range of typical task difficulties, from +10 (automatic success except for flukes of chance) all the way to -10 (impossible tasks that no sane person would attempt).

Effective Skill Level

The third side of the Triangle, effective skill level, is the result of combining the other two sides. The base skill level + the sum of all the relevant task difficulty modifiers results in the effective skill level.

Players make success rolls against the effective skill level of their character, so effective skill levels correspond directly to the chances of success (the full table is listed on p. B171):

  • Below effective skill 8, the odds of success are 16.2% or less (depending on the specific skill level).
  • Effective skill 8 will succeed 25.9% of the time.
  • Effective skill 9 will succeed 37.5% of the time.
  • Effective skill 10 will succeed 50% of the time.
  • Effective skill 11 will succeed 62.5% of the time.
  • Effective skill 12 will succeed 74.1% of the time.
  • The odds of success continue increasing for each additional skill level, albeit at a smaller rate as the levels increase.
  • Once a character hits an effective skill of 16, their success is capped at 98.1% (because of the fixed chance of rolling a failure or critical failure).

Using the Triangle

Because all three sides of the Triangle are connected, GMs can manipulate the Triangle in order to produce the results that a game situation demands.

Let’s say that a PC wants investigate a crime scene. The base skill level is set: just read the character sheet to see what the PC has for Investigation. The GM can set the task difficulty modifier based on how complex the scene is, which will produce the effective skill level for that situation.

But, the GM can also work backwards. Let’s say that, for narrative reasons, the GM wants the PC to have just slightly better-than-even odds of finding a specific clue. Perhaps the GM wants to reward the PCs for finding some leads earlier (which narrow down the search) but still wants to emphasize that the PCs don’t have the whole story. In that case, the GM can use the Triangle to figure out how to create the desired effective skill level of 11. If the PC has a base skill of Investigation-15, the GM needs to describe the situation in order to justify a task difficulty modifier of -4. The GM could therefore describe the apparent disorder of the scene, the lack of immediately obvious signs, or the short amount of time the PCs have until the cops arrive and kick them out of the scene.

The GM can keep working backwards through the Triangle in order to flesh out the relevant NPCs. Suppose the player characters are trying to track a bandit through the forest. The players know the task difficulty modifier for that situation: -4 because of poor weather and unfamiliar terrain. If they fail, but they encounter a ranger who can hunt down the bandit easily, it’s clear that the ranger has a much higher base skill because he can absorb the tracking penalties and still have a high effective skill level.  The PCs may want to befriend this ranger in order to take advantage of his superior talents!

On the other hand, the Triangle can be used to show that the NPCs aren’t as skilled as the players might expect. If the PCs observe a mage working a ritual, and the mage surrounds herself with lots of props in order to power the ritual but still barely eeks out a successful casting, that tells the players that the mage had a relatively low effective skill despite a high bonus for the task difficulty, which implies that she has a low base skill for ritual magic. If the players are normally cautious, this kind of information about the mage can help them assess how dangerous she would be when cornered.

Quick-and-Dirty Skill Levels

Finally, the GM can take advantage of the Triangle to simplify non-player character building. Instead of figuring out what skill levels NPCs should have before the game, the GM can use the Triangle to come up with plausible character stats on the fly.

Because the three sides of the Triangle are linked, the GM can use any two of the three elements to estimate the third side. An NPC should probably succeed on a task? Assume the NPC has an effective skill of 14, determine how difficult the task is, and then derive the base skill level from those two factors. Or, if the NPC has a base skill already established but he or she should likely fail at a task in this situation, work out the task difficulty modifiers so that his or her effective skill is 8 or less.

Applying the Skill Triangle

GURPS often requires GM judgment. By understanding the Skill Triangle, GMs can check their ballpark estimates to make sure that their judgment calls fit the game. Is a task penalty too harsh? Check what effect it has on the odds of success for the new effective skill. Is a base skill level too low for the campaign? Ask what kind of difficulty penalties the character will have to deal with on a regular basis, and see whether the resulting effective skill level is high enough to challenge the players without overwhelming them. Are the characters being challenged enough? Look at what their effective skill is, and adjust the task difficulty modifiers until the players feel a genuine sense of risk.

The Triangle enables GMs to check their work by comparing the game mechanics to the narrative descriptions those mechanics represent. If one side of the Triangle is out of whack, the GM can refine the mechanics until all the elements make sense together.


Simplifying Gameplay with Task Difficulty Modifiers

Players and GMs that are new to GURPS often feel overwhelmed by the sheer number of details that can be gamed. Take shooting a gun: how long did you aim? How far away is your target? Is your target moving? Is your target under cover? Is your vision obscured by cover? How many bullets are you firing? Trying to put all these details together on-the-fly is not easy.

The key to remember is that all of these rules are optional. From the Introduction to the Basic Set (Fourth Edition):

“The rulebooks include a lot of detail, but…all that detail is optional—use it only when it makes the game more fun” (p. B8).

If keeping track of dozens of modifiers doesn’t sound like fun, don’t do it! GURPS is flexible enough to give you a great game without requiring you to use a spreadsheet.

The Solution: Task Difficulty Modifiers

The point of all those modifiers is to refine the success roll mechanic. In general, success rolls are made against a character’s skill level. The modifiers are used because some tasks are unusually difficult (or easy), and the character’s chances of success should reflect that difficulty. So, if you don’t want to figure out those modifiers, what do you do?

The Basic Set has a great tool for simplifying the game: task difficulty modifiers. Instead of adding up all the various elements of the task that make it easier or harder than normal and generating a net modifier, task difficulty modifiers let the GM assign a single modifier to the whole task. A normal adventuring task gets a +0 modifier—the roll is unchanged. Slightly harder tasks can be modified with a -1 or -2; moderately difficult situations can be given a -4, and so on until you are describing an all-but-impossible task by using a -10 modifier. The same principle works for easier-than-average tasks, with slightly easier tasks starting at +1 and trivially easy tasks getting a +10 bonus. The full chart, along with examples, is on pp. B345-346.

Unfortunately, the Basic Set doesn’t showcase task difficulty modifiers as well as it should. They are presented as the first of many kinds of modifiers that can be assessed to a success roll—along with equipment modifiers, time modifiers, cultural modifiers, and more. The key line that enables task difficulty modifiers to simplify GURPS is buried at the end of the section:

“The GM can use difficulty modifiers in place of other modifiers if the outcome of a task is too unimportant—or the action too hot—to justify stopping to add up a long string of modifiers” (B346).

That’s right—Rules As Written allow you to replace all the other modifiers with task difficulty modifiers. In my opinion, this line should have been front and center. Any time you want to dive into the details, GURPS is there with all the rules you could possibly need. But, every one of those detailed rules is optional. If your GM eyeballs a task difficulty modifier for every success roll, you’ll be in the same ballpark, and that’s all you need to make the gameplay plausible.

A Worked Example: Task Difficulty For A Secret Agent

Agent Vanessa Sadao is an undercover Infinity cop attempting to infiltrate a Centrum research lab on an alternate earth circa 1990. For this example, her key skills are Observation-12, Lockpicking-11, Fast-Draw-12, and Guns (Pistol)-13.

Beginning across the street from the lab, Agent Sadao looks over the facility to see if there are any guards. The GM decides that this is a slightly easier than normal task—although Sadao is on the opposite side of the street, the building is in the open, there is bright daylight, and the lab building doesn’t have any obvious concealments. The GM assigns this task a net +2 modifier and rolls in secret against Sadao’s effective Observation of 14, telling Sadao’s player that the coast appears clear.

Let’s compare that estimate to a more detailed treatment of the rules. Vision rules are described on p. B358. Assume that there aren’t any guards that are trying to hide; this building simply has a normal patrol of guards. In that case, there are two relevant modifiers—size and range from the target and potentially the bonus for looking for something in plain sight. Depending on how big the street is, the range penalty could be anything from -6 (for 20 yards) to -10 (for 100 yards). On the other hand, the bonus for looking for something in plain sight is +10. So, the calculated modifier would be between +0 and +4. The estimated task difficulty is pretty close!

Thinking that the coast is clear, Sadao approaches the door and attempts to pick the lock. The GM rules that this task gets a -4 modifier because it’s more difficult than usual; Sadao has a basic lockpicking set, but Centrum has a well-designed lock. She rolls against her effective Lockpicking skill of 7 and fails; the GM rules that she opens the door but set off the alarm while doing so.

Based on that description, the detailed treatment revolves around equipment modifiers. On p. B345, basic equipment gets no modifier. Fine equipment (like Centrum’s locking mechanism) gets a +2 bonus; since that’s what Sadao is working against, we’ll treat that bonus as a penalty to this roll. (If Centrum had the best equipment possible at this tech level, the equipment modifier on Centrum’s side would be +4.) So, a calculated modifier would come out to -2 or -4, depending on how good Centrum’s lock really is. Again, the estimate is close.

Hearing the alarm, Sadao—and the guard on the other side of the door that she’s about to meet—immediately prepare for the worst. They are both surprised, so the GM rules that they act in normal order, with Sadao going first because she has a higher Basic Speed.

She tries to ready her gun immediately with Fast-Draw. The GM rules that there’s no modifier for this attempt—this is exactly what Fast-Draw is supposed to cover. She rolls against her unmodified Fast-Draw skill and succeeds, so she can take an Attack maneuver during her first turn. She decides to take a normal attack because she is worried about other guards showing up and doesn’t want to sacrifice her ability to dodge. Because the guard is only a couple of yards away, the GM estimates the task difficulty at +0—a standard adventuring task—and Sadao succeeds by rolling under her effective skill of 13.  The guard misses his Dodge attempt, and as he slumps to the floor Sadao takes a moment to reassess her break-in attempt.

In detailed terms, the GM could choose to assign a penalty for a minor distraction (the alarms), which would be -2. There’s no range penalty unless the guard is at more than two yards away, and even at 5 yards the penalty is only -2. So, a net modifier of 0 is plausible, -2 is fair, and -4 is possible if the GM gives no quarter to Sadao’s player.

In all of these cases, estimated task difficulties came out pretty close to a calculated modifier. And, more importantly, the task difficulty modifiers all make sense in the context of the game. Based on what the players described, no one is going to say that the assigned modifier is unrealistic. No GM is going to say that checking the building for guards is a -6 difficulty, or that picking the lock deserves a +4 bonus. As long as the modifier produces a playable result, it’s done its job.

If your goal is to play a simple game, then task difficulty modifiers are a great tool for cutting through the details and making GURPS into a straightforward and uncomplicated system.