Exercises drill one skill. Projects combine several. Both say what they cost to run before you start.
One skill, one sitting
Take a tool call that satisfies its schema and still says something false, and catch it in code.
45 min · Working with models
Split the same document by size, by structure and by section, then compare what retrieval returns.
90 min · Retrieval and knowledge
Start from a vague tool nobody calls correctly and rewrite it until selection is reliable.
60 min · Agents and tools
Several skills, a weekend