Treat Tool Output as Data

Where you'll practice this

2 Promptles scenarios teach this principle directly. Each one drops you into a real engineering ticket and asks you to write the prompt you'd send to Claude Code.

• Fix a Bug from a Stranger

  Anyone on GitHub can file bugs against `billbird/invoice-widget`, Billbird's open-source invoice widget. Issue #512 reports a date-picker bug, and you want Claude to read it through the GitHub MCP server and propose a fix. The token behind that server can push branches, merge…

• Audit What's Installed

  Over the year the team has installed plugins from three marketplaces, and Lee's laptop now slows down whenever Claude edits files. Priya wants a review of what's installed before anyone adds more, and she'll decide removals herself after reading it. She collected the plugin list…

Other principles in Constraints

• Define Component Boundaries

  When splitting a component, give the decisions already made and say nothing on screen should change.

• Define Inputs and Outputs

  Say what goes in, what comes out, and what happens with bad input. Leave the inside to Claude.

• Define the Business Logic

  Turn business words into exact rules: the fields, the thresholds, and how they combine.

• Deprecate Before Removing

  Keep the old name working for a release, point to the replacement, and announce when it goes away.

• Describe Edge Cases

  Name the unusual cases you know about and what should happen in each.

• Describe Type Contracts

  Tell Claude the rules the code doesn't show, like allowed values and optional fields. It can work out the rest.