Plan Mode & Extended Thinking

Two levers for getting better results on hard tasks: make Claude plan before touching code, and give it more thinking budget.

Plan Mode

A read-only analysis mode: Claude can read files, search, and reason — but cannot edit or run state-changing commands until you approve a plan.

Enter / exit

Method	How
Cycle permission modes	Shift+Tab (Normal → Accept Edits → Plan)
Start in plan mode	claude --permission-mode plan
Ask directly	”make a plan before implementing”

The flow

1. You describe the task; Claude explores the codebase
2. Claude presents a structured plan
3. You approve (Claude implements, session auto-named from the plan), edit the plan, or reject with feedback
4. On approval, mode switches back so Claude can edit files

When to use it

• Multi-file refactors, architectural changes
• Unfamiliar codebases — read the plan to learn the terrain
• Anything where a wrong start is expensive
• Reviewing an approach with teammates before burning tokens on implementation

opusplan

/model opusplan uses Opus for plan mode reasoning, then switches to Sonnet for execution — max intelligence for the decisions, lower cost for the typing.

Ultraplan (cloud planning)

For big features: ultraplan runs deep multi-agent planning in the cloud and returns a thorough implementation plan you execute locally. Available on the web/desktop surfaces — see docs: https://code.claude.com/docs/en/ultraplan

Extended Thinking

Ask Claude to think harder on genuinely hard problems — include the word “think” in your prompt, escalating:

think about this bug
think hard about the race condition here
ultrathink: design the migration strategy for zero downtime

More thinking = slower + more tokens, so reserve it for design decisions, gnarly bugs, and tradeoff analysis — not routine edits.

Effort level

/effort (or --effort) adjusts how much reasoning the model applies session-wide (low / medium / high). Lower effort = faster, fewer tokens, more direct answers. Subagents and teammates inherit the session’s effort.

Fast Mode

The opposite lever: /fast toggles fast mode (Opus with faster output) for quick iterations on well-understood tasks. Toggle off for hard problems.

Real Case: Zero-Downtime Schema Migration

1. Shift+Tab twice → plan mode
2. "ultrathink: we need to split the users table into users + profiles
   with zero downtime. Plan the full migration."
3. Claude explores models, migrations, query sites → presents 6-step plan
   (dual-write phase, backfill, cutover, cleanup)
4. You spot a missing index in step 3 → "edit plan: add index before backfill"
5. Approve → Claude implements step by step, running tests between steps

The plan cost a few thousand tokens and prevented a production incident.

🧠 Quick Recall

• Trick: “Plan before you touch.”
• Thinking ladder: think < think hard < ultrathink.
• opusplan = “Opus brains plan, Sonnet hands type.”

👨‍🏫 Teach It

• Show: Shift+Tab into plan mode, plan a refactor, edit the plan, approve.
• They’ll trip on: staying in plan mode and wondering why nothing gets edited.

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Learning path: ⬅ 09-context-window-management.md · Index · ➡ 11-real-world-workflows.md