Skill Checks
One engine resolves everything uncertain you do — swinging a sword, picking a lock, climbing a wall, patching a wound, scavenging a ruin. Attempt something risky and the game runs a skill check: it turns your relevant stats into a number, bends that number through a difficulty curve, rolls percentile dice against it, and tells you how well (or how badly) it went.
Three things to know up front:
- A point of skill is worth about the same no matter what you attempt. Everything rides the same curve.
- Results are graded. You get degrees of success and failure, and other systems use that magnitude.
- Nothing is ever guaranteed. The curve is soft at the edges, so a master can still whiff and a novice can still get lucky.
The pipeline
Building your number
Start with a weighted blend of stats. Each check cares about a few stats, each with a weight. Climbing leans on muscle, motion, and athletics; lockpicking leans on ego and security. Your base score is the weighted sum of your total values (including bonuses from effects, drugs, and cyberware):
$$ T_{\text{flat}} = \sum_i s_i \cdot w_i $$
Weights for a check normally add up to about $1.0$, so $T_{\text{flat}}$ lands on the same $0$–$100$ scale as a single stat.
Then fold in the situation. Every bonus and penalty collapses into one modifier, clamped to $[-30, +30]$:
$$ m = \mathrm{clamp}\big(\text{bonus} - \text{penalty} - d,\; -30,\; +30\big) $$
| Term | What it is |
|---|---|
| bonus | Help from your tool, weapon, or circumstance — a good lockpick, taking aim, hitting with momentum. |
| penalty | Resistance from the world — a defender's dodge, a stiff lock, hazards in the room. |
| d | An explicit task difficulty. Higher difficulty makes the check harder. |
Add the modifier to your flat score for the raw target number (capped at $95$ before the curve):
$$ T{\text{raw}} = \min\big(95,\; T{\text{flat}} + m\big) $$
The difficulty curve
The raw target gets pushed through a logistic (sigmoid) curve centered on $50$ to produce your real success chance:
$$ P = \mathrm{clamp}\left(\frac{100}{1 + e^{-0.08\,(T_{\text{raw}} - 50)}},\; 5,\; 95\right) $$
This curve is the core of the system. A raw $50$ is a coin flip. Above it your odds climb and below it they fall, but both ends compress hard toward a 5% floor and a 95% ceiling, so you can never fully guarantee or fully eliminate any outcome.
| Raw target | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Success % | 5 | 5 | 8 | 17 | 31 | 50 | 69 | 83 | 92 | 95 | 95 |
Where your points matter most: the curve is steepest between roughly $30$ and $70$. In that band each point of skill buys the most success — a few points can swing a hard fight. Outside it, you're paying skill for diminishing returns.
The roll, and luck
The game rolls percentile dice, $1$–$100$. You succeed if the roll is at or under your success chance.
Luck buys you a do-over. Your luck stat runs through the same sigmoid to produce a luck chance, and a hidden luck roll decides whether it pays off. If it does, you roll the check twice and keep the better (lower) roll:
$$ \text{roll} = \min(d_1, d_2) \quad \text{if the luck roll succeeds} $$
Luck doesn't improve any skill directly. It just quietly saves you from bad rolls more often.
Degrees of success
A check never returns a bare "pass" or "fail." It returns degrees, from the margin between your chance and your roll:
$$ \text{margin} = P - \text{roll}, \qquad \text{degrees} = \left\lfloor \frac{\text{margin}}{10} \right\rfloor \text{(nudged away from zero)} $$
There's no "degree 0" — the result is always at least $+1$ (success) or $-1$ (failure), and bigger magnitude means a more decisive outcome.
| Margin | Degrees | Meaning |
|---|---|---|
| +30 or more | +4 and up | Resounding success |
| +20 to +29 | +3 | Strong success |
| +10 to +19 | +2 | Solid success |
| 0 to +9 | +1 | Bare success |
| −1 to −9 | −1 | Near miss |
| −10 to −19 | −2 | Clear failure |
| −20 and worse | −3 and down | Disaster |
Systems use that magnitude for graduated results: how far you climb in one move, how much you heal, how much you scavenge.
Criticals
Separate from degrees: a roll is a critical whenever it's an exact multiple of 11 — $11, 22, 33, \dots, 99$. That's 9 of every 100 rolls (~9%). A critical can turn an ordinary hit into a wounding blow, or an ordinary fumble into something memorable, depending on which system called the check.
Worked example: picking a sturdy lock
Your weighted ego/security score comes to $48$. You're using a quality pick (bonus $+8$) against a sturdy lock (difficulty $12$):
$$ m = \mathrm{clamp}(8 - 0 - 12,\,-30,\,30) = -4 $$ $$ T_{\text{raw}} = 48 + (-4) = 44 $$ $$ P = \frac{100}{1 + e^{-0.08(44 - 50)}} \approx 38\% $$
So: roughly a 38% chance. With decent luck you'll occasionally re-roll your way through, and an exact multiple of 11 makes the attempt critical.
Where checks are used
The same engine resolves combat attacks, dodging, parrying, blocking, resisting stagger, climbing, scavenging, lockpicking, crafting, medical work, and sex. Each system just picks which stats matter and what counts as a bonus, penalty, or difficulty — see Damage Reduction, Sex, and Progression: Skills.