How do I make foot IK work on stairs in Godot?

Per foot, raycast down from the bone position. Use ground hit point + normal to drive a SkeletonIK3D or set bone pose via SkeletonModifier3D so each foot lands on its surface.

Should I use SkeletonIK3D or SkeletonModifier3D?

SkeletonModifier3D for custom logic. SkeletonIK3D is the legacy node and being phased out in favor of modular modifiers.

What about pelvis adjustment?

After IK lifts feet, lower the pelvis by the larger foot offset. Otherwise legs hyperextend. Apply pelvis offset before the IK pass so reach calculation is correct.

Fix: Godot CharacterBody3D Foot IK Fails On Stairs

Quick answer: Per-foot raycast down. Drive SkeletonModifier3D with hit position+normal. Lower pelvis by max(foot_offsets).

Walking up stairs, feet float above some steps and clip into others. Default animation has fixed-step heights; IK needs to follow surface.

The Fix

extends SkeletonModifier3D

@export var foot_l_bone: String = "FootL"
@export var foot_r_bone: String = "FootR"

func _process_modification():
    var sk = get_skeleton()
    _solve_foot(sk, foot_l_bone)
    _solve_foot(sk, foot_r_bone)

func _solve_foot(sk: Skeleton3D, name: String):
    var idx = sk.find_bone(name)
    if idx == -1: return
    var world = sk.global_transform * sk.get_bone_global_pose(idx)
    var from = world.origin + Vector3.UP * 0.5
    var to = world.origin - Vector3.UP * 0.5
    var ray = PhysicsRayQueryParameters3D.create(from, to)
    var hit = get_world_3d().direct_space_state.intersect_ray(ray)
    if hit:
        var p = sk.global_transform.affine_inverse() * hit.position
        sk.set_bone_pose_position(idx, p)

Reorder modifiers: pelvis adjuster first, foot solver second. Set per-foot blend weight when air-borne to disable the IK in flight.

Verifying

Walk up stairs. Each foot lands on its tread. Without the modifier: feet clip into steps.

“Raycast down. Set bone position. Feet land.”

Related Issues

For Skeleton3D bone reset, see bone reset. For AnimationTree travel, see travel.

Per-foot ray. Bone pose. Stairs land.