Real-time commands are immediate, non-blocking instructions that can be sent to Grbl at any time — even during motion or execution of a G-code program.
These commands are critical for pausing, resuming, checking status, or emergency stopping your CNC system without waiting for the current operation to finish.
Supported Real-Time Commands
| Command | Symbol | Description |
| Status Report | ? |
Returns current machine state, positions, and settings. Can be used repeatedly to track motion in real-time. |
| Cycle Start / Resume | ~ |
Resumes motion after a feed hold or a safety door pause. |
| Feed Hold (Pause) | ! |
Immediately pauses motion. This is a controlled stop that retains machine position and can be resumed with ~. |
| Soft Reset | Ctrl+X |
Instantly resets Grbl. All operations are stopped, and settings are reloaded. Must unlock with $X afterward. |
| Safety Door | 0x84 |
Tells Grbl the safety door is open. Motion and spindle pause safely. Resumed via door reopen/resume protocol. |
| Jog Cancel | 0x85 |
Immediately cancels any jogging operation in progress. |
| Feed Override +10% | 0x90 |
Increases the feed rate by 10%. |
| Feed Override -10% | 0x91 |
Decreases the feed rate by 10%. |
| Feed Override Reset | 0x92 |
Resets the feed rate to 100%. |
| Rapid Override -100% (disable) | 0x93 |
Disables rapid movement (sets rapid rate to 0%). |
| Rapid Override -50% | 0x94 |
Reduces rapid movement to 50% speed. |
| Rapid Override Reset | 0x95 |
Restores rapid movement to full speed. |
| Spindle Speed Override +10% | 0x99 |
Increases spindle speed by 10%. |
| Spindle Speed Override -10% | 0x9A |
Decreases spindle speed by 10%. |
| Spindle Speed Reset | 0x9B |
Resets spindle speed to 100%. |
| Toggle Spindle Stop | 0x9E |
Stops or restarts the spindle depending on its current state. |
| Toggle Flood Coolant | 0xA0 |
Turns flood coolant on or off. |
| Toggle Mist Coolant | 0xA1 |
Turns mist coolant on or off. |
Common Use Cases
-
Pause a job: Use
!to pause mid-cut safely. -
Check position: Send
?during a job to get real-time coordinates. -
Emergency recovery: Use
Ctrl+Xfor a fast reset in case of failure or crash. -
Adjust speeds: Use overrides to fine-tune feeds/spindle during a run.