Important Lessons from Claude Certification Exam Prep

Just passed the Claude Certified Architect (Foundations) exam. Total prep was about 6 hours, but to be upfront: I already had experience building agents and AI apps, so that number won't hold for everyone. What I used: claudecertificationguide.com/learn (not affiliated). The curriculum follows the 5 exam domains, and the Quick Reference page was great for last-minute review the night before. Please note that the questions in the site are way more concise and easy to understand than what you would get in a real exam. Exam basics for anyone considering it: 60 questions, 120 minutes, $125, pass mark 720/1000. Here are the 4 things that stuck with me most. They're useful whether or not you take the exam. 1. Anything that must happen every time belongs in a hook, not a prompt Prompts are suggestions. Hooks are guarantees. Claude Code has two main tool hooks: PreToolUse runs before a tool executes. It can block the call. Use it for validating inputs, enforcing formats, and protecting files. PostToolUse runs after the tool executes. It can't undo anything, but it's great for formatting, linting, and feeding results back to Claude. Example: a Python hook that stops Claude from ever editing .env files: #!/usr/bin/env python3 import json, sys event = json.load(sys.stdin) path = event.get("tool_input", {}).get("file_path", "") if path.endswith(".env"): print("Blocked: .env files are off-limits", file=sys.stderr) sys.exit(2) # exit code 2 = block the call, stderr goes to Claude Register it under PreToolUse in .claude/settings.json with the matcher Edit|Write . 2. Never let Claude review code in the same session that wrote it In the same session, Claude has its earlier reasoning in context and tends to defend its decisions instead of critiquing them. Start a fresh session for reviews. You'll get noticeably more honest feedback. Treat it like asking a different engineer for a code review. 3. Claude works as a CI reviewer with -p -p runs Claude non-interactively: it takes a prompt, prints the result, and exits. That makes it easy to drop into a pipeline: git diff main | claude -p "Review this diff for bugs and security issues" --output-format json 4. Use Plan Mode when you want analysis, not edits Ever asked "how would changing X affect this code?" and Claude just... changed X? Plan Mode is read-only: Claude can read, search, and analyze, but it can't edit files until you approve a plan. Press Shift+Tab to cycle modes (default → accept edits → plan) Or prefix your prompt with /plan Or start with claude --permission-mode plan I now use it by default in unfamiliar codebases. Happy to answer questions about the exam format or prep.