determinism

Original source / Raw SKILL.md

---
name: determinism
description: "Use when verifying outcomes with code instead of LLM judgment, versioning prompts with hashes, or ensuring reproducible agent behavior. Load for any critical verification. Scripts return boolean exit codes, not subjective assessments. Prompts use semantic versioning with SHA256 validation."
keywords: verification, deterministic, hash, version, reproducible, code-not-judgment
---

# Determinism

Reproducible outcomes through code verification and prompt versioning.

## Core Principle

> "Claude can run scripts without loading either the script or the PDF into context. And because code is deterministic, this workflow is consistent and repeatable." - Anthropic Engineering

## Instructions

1. Replace LLM judgment with script verification
2. Version prompts with semantic versioning
3. Hash-validate critical prompts: `scripts/validate-prompt.sh`
4. Use exit codes (0 = pass, 1 = fail), not text

## LLM Judgment vs Code Verification

| Task | LLM (Bad) | Code (Good) |
|------|-----------|-------------|
| Tests passed? | "The tests appear to pass" | `pytest; echo $?` → 0 or 1 |
| Valid JSON? | "This looks like valid JSON" | `python -c "json.load(f)"` |
| Server running? | "The server should be up" | `curl -s localhost/health` |

## References

| File | Load When |
|------|-----------|
| references/code-verification.md | Writing verification scripts |
| references/prompt-versioning.md | Versioning/hashing prompts |


---

## Referenced Files

> The following files are referenced in this skill and included for context.

### scripts/validate-prompt.sh

```bash
#!/bin/bash
# Validate prompt hash matches declared hash
# Usage: validate-prompt.sh PROMPT_FILE
# Exit: 0 = valid, 1 = invalid/no hash

PROMPT_FILE=${1:-"PROMPT.md"}

if [ ! -f "$PROMPT_FILE" ]; then
    echo "ERROR: File not found: $PROMPT_FILE"
    exit 1
fi

# Extract declared hash from header
DECLARED=$(grep -o 'SHA256: [a-f0-9]\+' "$PROMPT_FILE" | head -1 | cut -d' ' -f2)

if [ -z "$DECLARED" ]; then
    echo "WARN: No hash declared in $PROMPT_FILE"
    exit 0  # No hash = no validation (allow)
fi

# Calculate actual hash (strip comment lines)
CONTENT=$(grep -v '^<!--' "$PROMPT_FILE" | grep -v '^$')
ACTUAL=$(echo "$CONTENT" | shasum -a 256 | cut -d' ' -f1)

# Compare (declared may be truncated)
if [[ "$ACTUAL" == "$DECLARED"* ]]; then
    echo "PASS: Hash valid for $PROMPT_FILE"
    exit 0
else
    echo "FAIL: Hash mismatch in $PROMPT_FILE"
    echo "  Declared: $DECLARED"
    echo "  Actual:   ${ACTUAL:0:32}..."
    exit 1
fi

```