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Custom Tools
Plugins can register custom tools when OpenCode's built-in tools can't handle a specific job.
Once a custom tool is set up, it participates in the same tool system as the built-ins.
When Should You Make a Tool?
Custom tools are useful for specialized actions the agent performs repeatedly:
- Querying an internal database safely
- Calling a project-specific API
- Wrapping a complicated script behind a simpler interface
- Looking up metadata from a system the repo depends on
The main benefit is a clean, task-specific interface instead of forcing the agent to reinvent the same script every time it needs that action.
Every OpenCode custom tool comes from a plugin. Defining a new tool for a project/repo just means adding a small plugin file under .opencode/plugins/.