# Iterative planning fails **URL:** \ **Category:** Bug Reports\ **Tags:** cli\ **Created:** [November 26, 2025, 6:56pm UTC](https://forum.cursor.com/t/iterative-planning-fails/144328 "2025-11-26T18:56:43Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![art\_m](https://avatars.discourse-cdn.com/v4/letter/a/8e7dd6/32.png) [@art\_m](https://forum.cursor.com/u/art_m)\ **Post date:** [November 26, 2025, 6:56pm UTC](https://forum.cursor.com/t/iterative-planning-fails/144328/1 "2025-11-26T18:56:43Z")
### Where does the bug appear (feature/product)? Cursor CLI ### Describe the Bug iterative planning fails. when asking cursor to update a plan, cursor hangs. it can be restarted by prompting with something like “keep going” but this should have to happen each time. i asked cursor to analyze the problem and write a bug report and it appears to have done an excellent job of it. i attach the report below: # Bug Report: mcp\_create\_plan Tool - Plan Update Failures ## Summary The `mcp_create_plan` tool fails when attempting to update existing plans using the `old_str` and `new_str` parameters for partial plan updates. The tool consistently returns “invalid string to replace” errors even when the strings appear to match the plan content. ## Environment - Tool: `mcp_create_plan` - Operation: Updating existing plan using `old_str`/`new_str` parameters - Plan size: Large (~200+ lines, complex markdown structure) ## Steps to Reproduce 1. Create an initial plan using `mcp_create_plan` with `name`, `overview`, `plan`, and `todos` parameters 2. Attempt to update the plan using `old_str` and `new_str` parameters to replace a specific section 3. Observe error: “Received invalid string to replace in plan” ## Error Details ### Error Message ```auto Error calling tool: Received invalid string to replace in plan. The current contents are: [full plan content shown] ``` ### Observed Behavior - The tool shows the full current plan content in the error message - The error occurs even when `old_str` appears to exactly match content from the plan - Multiple attempts with different string matching approaches all fail - The tool sometimes times out instead of returning an error ### Example Failed Call ```python mcp_create_plan( old_str="### Phase 5: Entry Points & Compatibility\n1. Create `bin_py/` directory...", new_str="### Phase 5: State Management & Progress Tracking\n1. Create state management system..." ) ``` ## Root Cause Analysis ### Suspected Issues 1. **Whitespace/Formatting Mismatch** : The plan content may have different whitespace (tabs vs spaces, line endings) than what’s being matched 2. **String Matching Precision** : The tool requires exact string matches including all whitespace, which is fragile 3. **Plan Content Encoding** : Special characters or markdown formatting may not match exactly 4. **Large Plan Size** : The plan is very large (~200+ lines), which may cause issues with string matching 5. **Tool Implementation** : The tool may not properly normalize whitespace or handle markdown formatting differences ## Impact - **Severity** : High - Blocks iterative plan refinement - **Workaround** : Must recreate entire plan instead of making incremental updates - **User Experience** : Frustrating - requires re-entering entire plan content for small changes ## Suggested Fixes ### Option 1: Improve String Matching - Normalize whitespace (tabs→spaces, normalize line endings) - Trim leading/trailing whitespace before comparison - Use fuzzy matching or regex patterns instead of exact string matching ### Option 2: Add Section-Based Updates - Allow updates by section ID/header instead of exact string matching - Example: `update_section="Phase 5"` instead of `old_str`/`new_str` ### Option 3: Better Error Messages - Show diff between expected and actual content - Highlight where the mismatch occurs - Suggest closest matching sections ### Option 4: Alternative Update Mechanism - Provide a way to update specific fields (e.g., `update_plan_section`, `update_todos`) - Allow appending/prepending instead of replacement - Support JSON/YAML structured updates ## Workaround Currently, the only workaround is to recreate the entire plan with all content when updates are needed, which is inefficient for large plans. ## Additional Context - The tool works correctly for initial plan creation - The issue only occurs when attempting to update existing plans - Plan content includes complex markdown with code blocks, lists, and nested structures - Multiple attempts with different string extraction methods all failed ## Requested Priority **High** - This significantly impacts usability when refining plans iteratively. ### Steps to Reproduce Create an initial plan using mcp\_create\_plan with name, overview, plan, and todos parameters Attempt to update the plan using old\_str and new\_str parameters to replace a specific section Observe error: “Received invalid string to replace in plan” ### Expected Behavior things would work ### Operating System MacOS ### Current Cursor Version (Menu → About Cursor → Copy) Version: 2.1.36 VSCode Version: 1.105.1 Commit: 9cd7c8b6cebcbccc1242df211dee45a4b6fe15e0 Date: 2025-11-26T03:43:48.079Z Electron: 37.7.0 Chromium: 138.0.7204.251 Node.js: 22.20.0 V8: 13.8.258.32-electron.0 OS: Darwin arm64 25.0.0 ### For AI issues: which model did you use? composer-1 ### Does this stop you from using Cursor No - Cursor works, but with this issue ---
**Author:** ![deanrie](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/deanrie/32/1263_2.png) [@deanrie](https://forum.cursor.com/u/deanrie)\ **Post date:** [November 27, 2025, 1:14pm UTC](https://forum.cursor.com/t/iterative-planning-fails/144328/2 "2025-11-27T13:14:03Z")
Hey, thanks for the report. This is a known issue that affects plan updates. It matches a similar bug reported for IDE Plan Mode, where the problem is that the plan storage format differs from what’s displayed, causing string matching to fail. Temporary workarounds: - Recreate the entire plan instead of using `old_str/new_str` updates (as you’ve discovered) - Manually edit plans in .cursor/plans/ if saved to the workspace If you have a Request ID from one of the failed sessions, it would help with debugging. ---
**Author:** ![system](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/system/32/99069_2.png) [@system](https://forum.cursor.com/u/system)\ **Post date:** [December 19, 2025, 1:14pm UTC](https://forum.cursor.com/t/iterative-planning-fails/144328/3 "2025-12-19T13:14:50Z")
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