**The key idea:** You normally roll **d20 + the relevant modifier** and compare the result with a **Difficulty Class (DC)**. Matching the DC succeeds.
## Reading a roll
| Result compared with DC | Outcome |
|---|---|
| At least **10 above** DC | **Critical success** |
| **Equal to** DC through 9 above | **Success** |
| 1–9 below DC | **Failure** |
| At least **10 below** DC | **Critical failure** |
A natural **20** improves the result by **one degree**; a natural **1** worsens it by one degree. Neither automatically guarantees a particular outcome when the DC is extremely high or low. Example: an 18 against DC 20 fails; a 20 against DC 20 succeeds; a 30 against DC 20 critically succeeds. *(Player Core, pp. 392–393.)*
## What does my skill modifier mean?
| Proficiency | Proficiency bonus |
|---|---|
| Untrained | +0 |
| Trained | Level + 2 |
| Expert | Level + 4 |
| Master | Level + 6 |
| Legendary | Level + 8 |
Generally, **skill modifier = attribute modifier + proficiency bonus + applicable bonuses and penalties**. Some actions explicitly require being trained or better; if they do not, an untrained character can normally attempt them. For attacks, spellcasting and saves, use the matching statistic printed on your sheet rather than rebuilding it every turn. *(pp. 183–185, 392–396.)*
## Bonuses, penalties and unusual checks
- **Circumstance, status and item** bonuses: only the **largest bonus of each type** applies. Likewise, use the most severe penalty of a given type. Different types can combine.
- **Untyped penalties** usually accumulate; notably range penalties and multiple attack penalties both apply.
- **Flat check:** roll a d20 against a DC, **without normal modifiers**. Examples: concealed target DC 5; hidden target DC 11.
- **Secret check:** the GM rolls, so you don't automatically know whether your impression, investigation or stealth worked.
- **Saving throws:** Fortitude protects physical resilience; Reflex avoids sudden hazards; Will resists mental effects. A **basic saving throw** usually means critical success no damage, success half, failure full, critical failure double. *(pp. 392–397, 424–426.)*
## Hero Points
| Spend | Effect |
|---|---|
| **1 Hero Point** | Reroll your check; **use the second result**, even if it is worse. This is a fortune effect. |
| **All remaining Hero Points (minimum 1)** | **Heroic Recovery** when dying, at the permitted trigger. Stabilise at 0 HP without gaining/increasing wounded from that recovery. |
You normally start each session with **1 Hero Point**, can hold **at most 3**, and lose unspent points at the end of the session. Hero Points are separate from your three actions. *Sheet 07 has the full dying/recovery context.* *(pp. 404–405.)*
## At the table
1. Say **what you're trying to achieve**.
2. Identify the roll (the GM may set the DC or roll secretly).
3. Apply the correct modifier, status effects and other bonuses.
4. Read the **degree of success**, not merely "pass/fail".
5. If the result matters, consider whether a Hero Point reroll is worth it.
**Official sources:** *Starfinder Player Core*, pp. 183–185, 392–397, 404–405. **See also:** Sheets 01, 03, 06 and 07.