> ## Documentation Index > Fetch the complete documentation index at: https://docs.agi.tech/llms.txt > Use this file to discover all available pages before exploring further. # Task Design & Prompting > Write prompts the phone agent executes reliably. A phone task is one natural-language instruction executed on a real device. The difference between a flaky task and a reliable one is almost always the prompt. Five principles cover most of it. ## 1. One errand per task Size each [`phone_run_task`](/api-reference/tools/phone-run-task) to a single errand, and chain follow-ups in the same session. **✅ Good - focused:** ```text theme={null} Open Settings and report the current battery percentage. ``` **❌ Bad - a whole afternoon in one prompt:** ```text theme={null} Check my battery, then go through all my unread email, reply to the important ones, find me a flight to Denver, and update my calendar. ``` Oversized tasks burn their timeout, risk `terminal: "iteration_limit"`, and lose all progress on failure. Several tasks in one session get separate timeout budgets and keep completed results. See [Cross-app workflows](/guides/use-cases/cross-app-workflows). ## 2. Name apps and targets precisely The agent operates the real UI - ambiguity on a phone means tapping the wrong thing. ```text theme={null} Open WhatsApp (the green one, not WhatsApp Business) and find my chat with "Sam Rivera". If there are multiple matches, list them and ask me instead of guessing. ``` * Name the app as it appears on the device. When unsure what is installed, check first with [`phone_get_state`](/api-reference/tools/phone-get-state) - it lists launchable apps with label and package name. * Spell out contact names, account names, and which screen or tab to use. * Give the agent an explicit escape hatch: *"if you're unsure, stop and ask me"* - that surfaces as a handoff instead of a wrong guess. ## 3. Gate anything that acts Reading is safe to automate; **sending, buying, deleting, and changing settings deserve a confirmation gate in the prompt:** ```text theme={null} Draft the message and show it to me first. Wait for my OK before sending. ``` ```text theme={null} Stop and ask me before any login or payment screen, and before granting any permissions. ``` Sensitive moments the phone detects itself - logins, confirmations, CAPTCHAs - always come back as `needs_user_control` regardless. The gate covers the judgment calls above that bar. See [Security](/guides/best-practices/security). ## 4. Specify the output you want The task's `result` is your return value - define its shape: ```text theme={null} Check my three travel apps for SFO→DEN flights next Friday. Report the three cheapest as a list: airline / departure time / price, one per line. If an app shows no results, say so explicitly rather than skipping it. ``` Structured results make the next task's prompt (and your client's reasoning) precise. Ask for "not found" to be reported explicitly so silence never has to be interpreted. ## 5. Set boundaries for read-only work Tell the agent what *not* to do, so observation doesn't become action: ```text theme={null} Summarize my unread email from this morning. Don't reply to anything, don't archive anything, don't open links. ``` ## Quick checklist * [ ] One errand, not a workflow * [ ] Apps, contacts, and screens named exactly * [ ] Confirmation gate on anything that sends, buys, deletes, or changes settings * [ ] Output format specified, including the "not found" case * [ ] Read-only boundaries stated * [ ] "Ask me if unsure" escape hatch included ## Related What happens after you press go Timeouts and task sizing