defineTool

import { defineTool } from "@hellohelen-ai/goliath";

const tool = defineTool({
  name,
  description,
  parameters,
  writes,
  requires,
  execute,
  toModelOutput,
});

defineTool is an identity function that pins INPUT and OUTPUT from parameters and execute. The result is a GoliathTool.

Field	Type	Notes
name	string	What the conductor picks by. Also the key in the tools map
description	string	One sentence. Read on every step
parameters	z.ZodType<INPUT>	Flat: primitives and enums only
writes	boolean	true when the tool changes something. Goliath asks before running it
requires	string[]	Tools that must have run earlier in the turn
execute	(input, context) => OUTPUT | Promise<OUTPUT>	context.signal is the turn’s AbortSignal; context.context holds application run data
toModelOutput	(output: OUTPUT) => string	What the model sees. Default: key: value lines capped at 600 chars

outputMode: "content" opts into token-budgeted literal excerpts instead of the 600-character summary limit. context.resultBudget supplies maxTokens and the optional provider countTokens function. The harness also caps results after afterTool hooks and limits retrieved excerpts carried into subsequent model calls. Full recorded outputs remain available to application code.

requiresConfirmation: true declines a writing tool unless an explicit config-level or per-run confirmation handler approves it. Existing writing tools retain their prior default approval behavior. This flag does not replace writes: true.

See the Tools guide for what makes a tool work on a small model.