See what actually changes when you improve your prompts — not just different wording.
Inspired by the Rashomon effect — the idea that the same event can produce different outcomes depending on perspective. rashomon makes those differences explicit and comparable.
- Spending too much time on trial-and-error with prompts?
- Read best practices but not sure how they apply to your case?
- Want proof that your changes actually made things better?
rashomon analyzes, improves, and compares prompts—so you can see what actually changed, and whether it matters.
rashomon is designed for:
- Developers using Claude Code daily
- Teams iterating on complex prompts (coding, analysis, writing)
- Anyone who wants evidence, not vibes, when improving prompts
Not ideal if:
- You don't use git
- You want one-shot prompt rewriting without comparison
/rashomon Write a function to sort an array
1. Detected Issues
- BP-002 (Vague Instructions): Sort order, language, and error handling not specified
- BP-003 (Missing Output Format): No expected output structure defined
2. Improved Prompt
Write a TypeScript function that sorts a number array in ascending order.
- Return empty array for empty input
- Include JSDoc comments
- Output: function code with example usage
3. Comparison Report
| Aspect | Original | Improved |
|---|---|---|
| Type definitions | None | Included |
| Edge case handling | None | Included |
| Documentation | None | JSDoc added |
Result: Structural Improvement - The optimization made a meaningful difference.
/rashomon Summarize this article in 3 bullet points
Result: Variance - Prompt was already well-scoped; differences were stylistic only.
Requires Claude Code (this is a Claude Code plugin)
# 1. Start Claude Code
claude
# 2. Install the marketplace
/plugin marketplace add shinpr/rashomon
# 3. Install plugin
/plugin install rashomon@rashomon
# 4. Restart session (required)
# Exit and restart Claude Code/rashomon Your prompt here
From a file:
/rashomon Generate code following this skill: ./prompts/my-skill.md
For complex tasks that need more time, just mention it in natural language:
/rashomon Refactor the entire authentication module. This might take a while.
Your Prompt
↓
1. Analyze → Detect common issues automatically
↓
2. Improve → Generate optimized version
↓
3. Run Both → Execute in isolated environments
↓
4. Compare → Show what actually changed
↓
Comparison Report
Technical Details
rashomon uses git worktrees to run both prompts in completely separate environments. A worktree is a Git feature that creates independent working directories from the same repository—this ensures the two executions don't interfere with each other.
Both prompts run simultaneously via Claude Code subagents, so comparison time is roughly the same as a single execution, not double.
Main Orchestrator
├── prompt-analyzer (analyzes and optimizes)
├── prompt-executor ×2 (runs in parallel)
└── report-generator (compares results)
rashomon checks for 8 common prompt issues:
| Priority | Issues |
|---|---|
| Critical | Negative instructions ("don't do X"), vague instructions, missing output format |
| High Impact | Unstructured prompts, missing context, complex tasks without breakdown |
| Enhancement | Biased examples, no permission for uncertainty |
Pattern Details (BP-001 through BP-008)
| ID | Pattern | Problem | Fix |
|---|---|---|---|
| BP-001 | Negative Instructions | "Don't do X" often backfires—LLMs focus on what's mentioned | Reframe positively: "Don't include opinions" → "Include only factual information" |
| BP-002 | Vague Instructions | Missing specifics cause high output variance | Add explicit constraints: format, length, scope, tone |
| BP-003 | Missing Output Format | No format spec leads to inconsistent outputs | Define expected structure: JSON schema, section headers, etc. |
| ID | Pattern | Problem | Fix |
|---|---|---|---|
| BP-004 | Unstructured Prompt | Wall of text obscures priorities | Apply 4-block pattern: Context / Task / Constraints / Output Format |
| BP-005 | Missing Context | No background leads to wrong assumptions | Add purpose, audience, relevant constraints |
| BP-006 | Complex Task | Undivided complex tasks have higher error rates | Break into steps with quality checkpoints |
| ID | Pattern | Problem | Fix |
|---|---|---|---|
| BP-007 | Biased Examples | Homogeneous examples cause overfitting | Diversify: include edge cases, different formats |
| BP-008 | No Uncertainty Permission | No "I don't know" option causes hallucination | Add: "If unsure, say so" |
Not all differences are improvements. rashomon classifies results into three categories:
| Classification | Meaning | Recommendation |
|---|---|---|
| Structural | Real improvement in accuracy, completeness, or quality | Use the optimized prompt |
| Expressive | Different wording, same substance | Either version is fine |
| Variance | Just normal LLM randomness | Original prompt was already good |
Classification is based on:
- Whether detected issues (BP patterns) were resolved
- Output completeness and constraint adherence
- Consistency across multiple evaluation signals
About Knowledge Base
rashomon learns from your project over time.
Location: .claude/.rashomon/prompt-knowledge.yaml
How it works:
- Automatically enabled when the file exists
- Stores project-specific patterns (not generic best practices)
- Referenced during analysis, updated after comparisons
- Max 20 entries, lowest-confidence ones removed first
Key principle: Old knowledge isn't automatically removed. Patterns that have worked for a long time are often the most valuable.
Troubleshooting
If rashomon exits unexpectedly, temporary directories might remain:
# Worktrees are stored in system temp directory
# Clean up manually if needed:
rm -rf ${TMPDIR:-/tmp}/worktree-rashomon-*For complex prompts that need more time, mention it when invoking:
/rashomon Complex task here. This might take longer than usual.
rashomon requires a git repository. Initialize one with:
git init- Git 2.5+
- Claude Code
- Must run inside a git repository
MIT