Plan mode provides read-only exploration. No file modifications. You map dependencies, evaluate approaches, and design the solution before touching anything. Then switch to direct execution to implement.
The decision is not “should I plan?” It is “does this task have uncertainty?” If yes, plan mode. If the solution is already known, direct execution.
The Data
A team tracked 100 tasks across both modes:
| Mode + Task type | Success without rollback |
|---|---|
| Plan mode → complex tasks (30) | 87% |
| Direct execution → complex tasks (20) | 45% |
| Plan mode → simple tasks (15) | 100%, but 2x slower |
| Direct execution → simple tasks (35) | 97% |
Complex tasks without planning fail more than half the time. Simple tasks with unnecessary planning waste double the time for 3% more success. Mode must match task complexity.
When to Use Plan Mode
Multiple valid approaches exist. “Add caching to the API layer” has three options — Redis, in-memory, file-based — each with different implications for the database and session layers. Plan mode explores each option’s impact before committing.
Codebase is unfamiliar. A new team member asked to implement a cross-module feature has never seen the code. Plan mode maps the structure, boundaries, and conventions before changes.
Architectural decisions needed. Restructuring a monolith into 3 microservices across 45+ files with complex interdependencies. One developer skipped planning, used direct execution, and after 30 minutes of changes across 12 files discovered the approach conflicted with the session management system. Full rollback. Plan mode would have found that conflict before any changes were made.
Many files with interdependencies. Changes that cascade across the codebase need a map of what connects to what.
When to Skip Plan Mode
Solution is known. A stack trace points to line 42, the fix is obvious. Direct execution.
Scope is clear and small. Fixing a typo, updating a constant, adding a known test case. No exploration needed.
Single-file with obvious change. No dependencies to map, no approaches to evaluate.
The criterion is not file count, not estimated time, not developer seniority. It is task complexity and uncertainty. A 1-file change in unfamiliar code might need plan mode. A 20-file change with a known pattern might not.
The Plan → Explore → Direct Workflow
For large codebases (500+ files), even plan mode can fill the context with exploration output. The combined workflow solves this:
- Plan mode — establishes the read-only safety context
- Explore subagent — performs verbose codebase discovery in isolated context, returns only a summary to the main session
- Direct execution — implements changes with the main context preserved for editing
The Explore subagent is critical for large-scale exploration. Without it, reading hundreds of files fills the main context, leaving no room for the design or implementation phase. The subagent’s summary preserves the context budget.
/compact is a lossy alternative — it compresses the conversation but may discard exploration findings needed for design. The Explore subagent is non-lossy: full results exist in the subagent’s context, and the summary provides what the main session needs.
Note: plan mode is read-only. It cannot implement changes. The workflow must switch to direct execution for the implementation phase. Subagents also do not have unlimited context — their value is isolation and summary, not greater capacity.
The “Always Plan” Anti-Pattern
A team lead proposes plan mode for every task. This is wrong. Plan mode on simple tasks wastes time — the exploration has zero value when the solution is already known. The data shows 2x overhead on simple tasks with no quality improvement (100% vs 97%).
The reverse anti-pattern — never planning — is worse. Direct execution on architectural refactors causes 55% rollback rate. But “always plan” overcorrects by adding overhead to the 35% of tasks that do not need it.
Combining for Dual Constraints
Teams need both quality (no rollbacks) and velocity (fast completion). The combination:
- Complex/uncertain tasks: Plan mode to investigate, then direct execution to implement. Quality-first approach prevents rollbacks.
- Simple/known tasks: Direct execution immediately. Velocity-first approach avoids unnecessary overhead.
This satisfies both constraints by applying each mode where it provides value.
One-liner: Plan mode when you do not know the answer yet; direct execution when you do — matching mode to task uncertainty prevents both the 55% rollback rate and the 2x overhead.