> For AI agents: guidance on navigating Viam documentation is available at https://docs.viam.com/llms.txt. # Replay mode Step through saved motion plans in the 3D scene, including the obstacles each plan was planned against. > Source: https://docs.viam.com/visualization/3d-scene/replay-mode/ Replay mode loads plans the motion service saved and steps through them in the scene. It shows a plan the motion service already computed, whatever requested it: your code, a module, the CLI, or [Move mode](/visualization/3d-scene/move-mode/). Replay also shows something the scene can't show otherwise: the obstacles a request passed in its `WorldState`. Those obstacles never appear in the live scene, but a saved plan records them, and a replayed plan draws them in place. Replay needs saved plans: the motion service has to be configured to save them, and the files synced to the cloud. To set that up, see [Save plans for replay](/motion-planning/visualize-a-motion-plan/#save-plans-for-replay). ## Load and play a plan The **Import from data** dialog lists cloud-synced plan files tagged `motion-plan`, which are plans that succeeded, and `motion-plan-err`, which are plans that failed. It searches the current machine by default; widen it to the whole organization if the plan ran elsewhere. You can also upload a plan file from your computer. Select a loaded plan to display it in the scene. A failed plan has no trajectory, so it renders the scene it planned against with nothing to step through. Play, pause, step, or scrub through a plan: each step moves the arm's links and joints to their pose at that waypoint, with the plan's obstacles in place. ## What replay shows Replay steps through the plan's waypoints only. A plan with many closely spaced waypoints, such as one with a linear constraint, plays smoothly. A plan with just a start and an end jumps between them, so replay won't show how the arm got around an obstacle. To see the motion between waypoints, preview the same move in [Move mode](/visualization/3d-scene/move-mode/), where you can switch to **Interpolated** playback. Saved plans include previews from Move mode, even ones you never ran, so the import list can include plans that never moved the machine. A loaded plan appears only in Replay mode. Switching to another mode hides it, so it doesn't affect the live scene or the **Collisions** readout in Move mode. ## Debug a plan with Inspect IK When a plan fails, the error tells you what collided, but not always whether the goal itself is impossible or only the route to it is blocked. When a plan succeeds but the arm takes a route you didn't expect, nothing tells you why. **Inspect IK** answers both. Each plan in Replay mode's list has an **Inspect IK** button, which reruns the inverse kinematics (IK) for the plan's request and lists every candidate it finds: a set of joint positions that would put the arm at the goal. Candidates are grouped by seed. Each seed is a different starting point for the search, so different seeds tend to find different joint positions, and sometimes the same ones, so the same candidate can appear more than once. You can also sort all candidates by cost: roughly how far the arm's joints would have to move from where they started. Unscored candidates sort last. Each candidate gets one of three statuses: - **Valid**: the end pose and the direct path to it are both clear. - **Path blocked**: the end pose is reachable, but the direct path to it fails, by colliding with something or by violating a constraint in the request. - **Goal blocked**: the end pose itself collides, with an obstacle or with another part of the machine. Candidates marked **unscored** are also goal blocked: the solver found no joint positions at all from that seed, so there's no pose to show. Read the overall pattern first: - **Every candidate is goal blocked**: the goal is the problem. No joint positions reach it without a collision, so move the target or the obstacle. - **Most candidates are path blocked, and none are valid**: the goal is reachable, but the route is obstructed. Look at what the path runs into. - **The arm took a surprising route**: sort by cost. The planner moves straight to the cheapest valid candidate, unless every valid one costs far more than the cheapest candidate overall; then it searches for a route around the obstacles instead, and the result can have more waypoints. If the cheapest candidates are path blocked, something was in the way of the shorter routes. Select a candidate to see it in the scene and read its failure detail, which names the geometries or the constraint involved. For a goal-blocked candidate, you can show its start and failing poses. For a valid or path-blocked candidate, you can also play its direct path, interpolated over the number of steps you choose. For a path-blocked candidate, you can show its **Last good** pose: the last pose on the path before the failure. The path shows the blocked route, so the arm passes through whatever blocks it. The direct path is a straight line in joint space, not the path the planner would take. With a linear or orientation constraint in the request, nearly every direct path violates the constraint, so most candidates show as path blocked whatever else is in the way. For those plans, read each candidate's failure detail before drawing conclusions. For more about how Viam's motion planner chooses among candidates and plans a route, see [How motion planning works](/motion-planning/how-planning-works/). ## What's next - [Save plans for replay](/motion-planning/visualize-a-motion-plan/#save-plans-for-replay): configure the motion service to save plans and sync them. - [Move mode](/visualization/3d-scene/move-mode/): plan a move from the scene and preview it, including the motion between waypoints. - [Debug a motion plan](/motion-planning/debug-motion-plan/): check frames, obstacles, and reach when a plan fails.