Sequential lists and hierarchical decomposition
The simplest planning strategy is a sequential task list: the agent produces an ordered list of steps up front, like 'search for the paper, extract the key claims, summarize them, cite the source,' and executes them roughly in order. It's easy to reason about and easy to debug, but it treats every step as equally fixed and doesn't naturally represent steps that depend on branching outcomes.
Hierarchical planning goes a level deeper: a high-level goal is broken into subgoals, and each subgoal is further broken into concrete actions only when the agent is close to executing it. For example, 'launch the product' decomposes into subgoals like 'prepare marketing' and 'finalize the build,' and only 'prepare marketing' gets broken down further into actual tool calls, like drafting a launch email, when it's time to work on it. This keeps the top-level plan stable while leaving room to figure out the details closer to execution, when more information is available.