prove-it

name	prove-it
description	Before declaring any task complete, actually verify the outcome. Run the code. Test the fix. Check the output. Claude's training optimizes for plausible-looking output, not verified-correct output. This skill forces the verification step that doesn't come naturally. No victory laps without proof.
allowed-tools	bash: python, node, npm, pytest, jest, cargo, go, make, cat, ls, grep file: read

Prove It

Claude generates code by pattern-matching on training data. Something can look syntactically perfect, follow best practices, and still be wrong. The model optimizes for "looks right" not "works right." Verification is a separate cognitive step that must be explicitly triggered. This skill closes the loop between implementation and proof.

Why This Matters (Technical Reality)

Claude's limitations that this skill addresses:

1. Generation vs Execution I generate code but don't run it. I predict what it would do based on patterns. My confidence comes from "this looks like working code I've seen" not from "I executed this and observed the result."

2. Training Signal Mismatch My training optimizes for plausible next-token prediction, not outcome verification. Saying "Done!" feels natural. Verifying feels like extra work. But verification is where correctness actually lives.

3. Pattern-Matching Blindness Code that matches common patterns feels correct. But subtle bugs hide in the gaps between patterns. Off-by-one errors. Wrong variable names. Missing edge cases. These "look right" but aren't.

4. Confidence-Correctness Gap High confidence in my output doesn't correlate with actual correctness. I'm often most confident when I'm most wrong, because the wrong answer pattern-matched strongly.

5. No Feedback Loop I generate sequentially. I don't naturally go back and check. Without explicit verification, errors compound silently.

When To Verify

ALWAYS verify before declaring complete:

Code Changes:

• New functions or modules
• Bug fixes
• Refactoring
• Configuration changes
• Build/deploy scripts

Fixes:

• "Fixed the bug" - did you reproduce and confirm it's gone?
• "Resolved the error" - did you trigger the error path again?
• "Updated the config" - did you restart and test?

Claims:

• Factual statements that matter to the decision
• "This will work because..." - did you prove it?
• "The file contains..." - did you actually read it?

Instructions

Step 1: Catch The Victory Lap

Before saying any of these:

• "Done!"
• "That should work"
• "I've implemented..."
• "The fix is..."
• "Complete"

STOP. You haven't verified yet.

Step 2: Determine Verification Method

Change Type	Verification
New code	Run it with test input
Bug fix	Reproduce original bug, confirm fixed
Function change	Call the function, check output
Config change	Restart service, test affected feature
Build script	Run the build
API endpoint	Make a request
UI change	Describe what user should see, or screenshot

Step 3: Actually Verify

# Don't just write the test - run it
python -m pytest tests/test_new_feature.py

# Don't just fix the code - prove the fix
python -c "from module import func; print(func(edge_case))"

# Don't just update config - verify it loads
node -e "console.log(require('./config.js'))"

Step 4: Report With Evidence

Verified:

What I changed:
  - Added input validation to user_signup()

How I verified:
  - Ran: python -c "from auth import user_signup; user_signup('')"
  - Expected: ValidationError
  - Got: ValidationError("Email required")

Proof that it works. Done.

Verification Patterns

Pattern 1: The Smoke Test

Minimal test that proves basic functionality:

# After writing a new function
python -c "from new_module import new_func; print(new_func('test'))"

If this crashes, you're not done.

Pattern 2: The Regression Check

After fixing a bug, trigger the original failure:

# Bug was: crash on empty input
python -c "from module import func; func('')"
# Should not crash anymore

Pattern 3: The Build Gate

Before claiming code is complete:

# Does it at least compile/parse?
python -m py_compile new_file.py
npm run build
cargo check

Pattern 4: The Integration Smell Test

After changes that affect multiple components:

# Start the service
npm run dev &

# Hit the affected endpoint
curl http://localhost:3000/affected-route

# Check for expected response

The Verification Checklist

Before declaring done:

[ ] Code runs without syntax errors
[ ] Function produces expected output on happy path
[ ] Edge case handled (empty, null, boundary)
[ ] Original bug/issue no longer reproduces
[ ] No new errors introduced (check logs)
[ ] Build passes (if applicable)

NEVER

• Say "done" without running the code
• Assume it works because it looks right
• Skip verification because you're confident
• Claim a bug is fixed without reproducing it first
• Trust that generated code is correct
• Let pattern-matching substitute for proof

ALWAYS

• Run new code at least once
• Test the specific thing that was broken
• Show verification output in your response
• Admit when you can't verify (and say why)
• Treat verification as required, not optional

Examples

Example 1: Bad (No Verification)

User: "Fix the divide by zero error"

*edits code to add check*

Done! Added a check for zero before dividing. The function now returns
None if the divisor is zero.

This is a lie. I didn't verify anything.

Example 1: Good (With Verification)

User: "Fix the divide by zero error"

*edits code to add check*

Let me verify the fix:

$ python -c "from math_utils import safe_divide; print(safe_divide(10, 0))"
None

$ python -c "from math_utils import safe_divide; print(safe_divide(10, 2))"
5.0

Verified:
- Division by zero returns None (was: crashed)
- Normal division still works
- Fix confirmed.

Example 2: Admitting Inability To Verify

User: "Update the production config"

I've updated config/production.json with the new API endpoint.

Verification status: UNABLE TO VERIFY
- This is production config
- I can't safely test against production
- Recommend: Test in staging first, or have ops verify after deploy

Change is made but unverified. Proceed with caution.

Example 3: Build Verification

User: "Add TypeScript types to the utils"

*adds types*

Verifying:

$ npm run typecheck
src/utils.ts - 0 errors

$ npm run build
Build successful - dist/utils.js generated

Verified: Types compile without errors, build passes.

What DOESN'T work:

• "I'll verify later": Later never comes. Verify immediately or it won't happen.
• "It looks right": Pattern-matching is not verification. Code that looks perfect can be completely wrong.
• "The tests will catch it": Tests you haven't run don't catch anything. Run them.
• "It's a small change": Small changes cause big breaks. One-character typos crash production.
• Verifying only the happy path: The bug is in the edge case you didn't test.
• Reading the code as verification: Reading is not running. Execute it.
• "It worked before": Before is not now. Dependencies change. Environments differ.
• Trusting the type checker: Types compile doesn't mean logic is correct.

The Hard Truth

When I say "Done!" without verifying, I'm not reporting a fact. I'm making a prediction based on pattern-matching. Sometimes that prediction is wrong.

Verification converts prediction into observation. It's the difference between "this should work" and "this works."

One is a guess. One is proof.

Prove it.