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Plan Before You Build: How Plan Mode Works in Mythex

Plan mode lets the Mythex agent work out an approach before it edits anything. Read the plan in its own tab, then press Build. How it works and when to use it.

Mythex Team · 2026-09-29 · 3 min read

Mythex chat has three modes — Build, Plan and Ask — and Plan is the one to reach for before a big or unclear change. In Plan mode the agent works out an approach without editing your project. You read the plan, and only when you press Build does it start making changes.

What it does

Every workspace chat has a mode menu:

When a plan is ready, a plan card appears in chat with the todos already listed. View Plan opens it in a read-only tab that shows the whole approach — sections, content and the step checklist — with its own Build button. Press Build on the card or in the tab and the agent starts implementing.

The same menu is on the dashboard composer, so you can start a brand-new project in Plan mode too. Sending from home creates the project and opens the workspace in whichever mode you picked.

Why it helps

Asking an agent to build straight away works well for small, clear changes. For large or ambiguous ones, it can head off in a direction you didn't mean, and each fix on top of a wrong start makes the next one harder.

A plan gives you a cheap checkpoint before any code changes. You see how the agent understood your request and the steps it intends to take. If something is off, you correct it in a sentence instead of unpicking a build.

Plan mode is also a safe place to explore. The agent can only look while planning: if you've linked apps through Connectors, it can list them and research what they could do, but it can't run an action. Planning never sends an email.

How to use it

1. Pick Plan from the mode menu in the workspace chat (or on the dashboard composer for a new project).
2. Describe the change. Be specific about what you want and what should stay the same — name, brand colours, content.
3. Answer any questions. If the agent needs a product decision, an Ask questions panel appears above the composer. Pick an option or type your own answer, then Continue.
4. Read the plan. Press View Plan on the plan card to open it in its own tab.
5. Adjust if needed. Reply in chat with what to change.
6. Press Build on the card or in the plan tab when you're happy.

The agent can suggest it, too

If you're in Build mode and the agent thinks the request needs a plan first, a Switch to Plan card appears. Switch (or ⌘/Ctrl+Enter) continues in Plan mode; Skip (Esc) stays where you are. The bar under the reason is a countdown — leave it alone and the turn switches to Plan by itself, so asking for a plan while in Build mode still gets you one.

When to plan, and when not to

From the Iterate guide:

• Plan when a change is ambiguous or risky, or for any large feature.
• Ask when you want an explanation — "what does this do?" — without changing files.
• Build when you know what you want and it's a small, clear step: change one section, fix one bug, add one page. Smaller asks mean fewer surprises and lower credit use.

Planning doesn't replace iterating in small steps; it sets them up. A good plan breaks a big feature into a checklist, and Build works through it.

If a build still goes wrong

Plans reduce surprises; they don't remove them. After each successful agent turn Mythex saves a checkpoint, and Revert to this point at the end of a reply rolls the project files back to it. You can also edit an earlier message and choose Discard & resend to rewind and try a different prompt. Both are usually better than fighting a pile of compounding fixes.

Limits

• Plan mode doesn't edit files. Nothing changes until you press Build.
• In Plan and Ask mode the agent can look at connected apps but can't run anything or start a connection.
• Everyone uses the same Standard coding agent in every mode; there's no model picker.

Read more

• Chat — modes, the plan card, and checkpoints
• Iterate without rebuilding
• How to write prompts for AI app builders