# undo
## Description
Reverts the last action in a session. Supports undoing generate-image calls, parameter changes, and other operations up to 50 steps deep. Works in conjunction with redo for full command history navigation.
## Input Schema
```typescript
{
sessionId: string // Required: e.g., "session-2025-12-11-001"
}
```
**Required**: `sessionId`
**Optional**: (none)
## Output Schema
```typescript
{
content: [
{
type: 'text',
text: JSON
}
]
}
```
**JSON structure:**
```typescript
{
success: boolean,
sessionId: string,
undoneAction: {
type: string, // e.g., "generate", "parameter_change", "rollback"
description: string,
timestamp: string
},
previousState: {
iterationIndex: number,
iterationCount: number,
lastPrompt?: string
},
undoStackRemaining: number, // How many more undos available
redoStackAvailable: number // How many redos now available
}
```
## Examples
### Example 1: Undo last generation
**Input:**
```json
{
"sessionId": "session-2025-12-11-001"
}
```
**Output:**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":true,\"sessionId\":\"session-2025-12-11-001\",\"undoneAction\":{\"type\":\"generate\",\"description\":\"Generated image with prompt 'Cyberpunk city at night'\",\"timestamp\":\"2025-12-11T14:50:15.123Z\"},\"previousState\":{\"iterationIndex\":9,\"iterationCount\":10,\"lastPrompt\":\"Mountain landscape with aurora borealis\"},\"undoStackRemaining\":9,\"redoStackAvailable\":1}"
}
]
}
```
### Example 2: Undo parameter change
**Input:**
```json
{
"sessionId": "session-2025-12-11-002"
}
```
**Output:**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":true,\"sessionId\":\"session-2025-12-11-002\",\"undoneAction\":{\"type\":\"parameter_change\",\"description\":\"Changed guidance_scale from 7.5 to 12.0\",\"timestamp\":\"2025-12-11T14:48:30.456Z\"},\"previousState\":{\"iterationIndex\":4,\"iterationCount\":5},\"undoStackRemaining\":3,\"redoStackAvailable\":1}"
}
]
}
```
### Example 3: Undo when nothing to undo
**Input:**
```json
{
"sessionId": "session-2025-12-11-003"
}
```
**Output:**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":false,\"error\":\"Nothing to undo\",\"sessionId\":\"session-2025-12-11-003\",\"undoStackRemaining\":0,\"redoStackAvailable\":0}"
}
]
}
```
### Example 4: Undo multiple times (third undo in session)
**Input:**
```json
{
"sessionId": "session-2025-12-11-001"
}
```
**Output:**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":true,\"sessionId\":\"session-2025-12-11-001\",\"undoneAction\":{\"type\":\"generate\",\"description\":\"Generated image with prompt 'Landscape variant 3'\",\"timestamp\":\"2025-12-11T14:45:22.789Z\"},\"previousState\":{\"iterationIndex\":7,\"iterationCount\":8,\"lastPrompt\":\"Landscape variant 2\"},\"undoStackRemaining\":6,\"redoStackAvailable\":3}"
}
]
}
```
## Error Cases
- **Session not found**: Invalid sessionId
- **Nothing to undo**: Undo stack is empty (fresh session or all undos exhausted)
- **Session in inconsistent state**: Recovery attempted automatically
## Notes
- Maximum undo depth: 50 operations per session
- Undo stack includes: image generation, parameter changes, rollbacks, etc.
- Each undo operation pushes the previous state onto the redo stack
- Redo stack is cleared if a new action is performed (normal editor behavior)
- Very fast operation, typically <10ms
- Useful for iterative exploration without losing work
- Pair with redo for full command history navigation
