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DeepSeek Harness Docs

Build a tool

Create the tool plugin

Section titled “Create the tool plugin”

Replace scratch-plugin/src/my-plugin.ts with:

import type { Context } from '@deepseek-ai/cordis'
import { defineTool } from '@deepseek-ai/dsh-tools'


export const name = 'greet-tool'
export const inject = ['tools']


export function apply(ctx: Context) {
  ctx.tools.register(defineTool({
    name: 'greet',
    description: 'Greet someone by name.',
    parameters: {
      name: { type: 'string', required: true, description: 'The name to greet' },
    },
    output: {
      schema: { type: 'string' },
      render: (_args, value) => [{ type: 'text', text: value }],
    },
    async execute(args) {
      return `Hello, ${args.name}!`
    },
  }))
}

inject makes Cordis wait for the tool registry. defineTool infers and validates args from parameters; execute returns the canonical value declared by output.schema, and output.render converts that value to model-facing content.

Run and call the tool

Section titled “Run and call the tool”

Restart the development command if it is not running:

Terminal window
pnpm dsh web --patch ./scratch-plugin/cordis.yml

Open http://127.0.0.1:3080 and ask: Use the greet tool to greet Ada. The model can call greet and receives Hello, Ada! as the tool result.

Next steps

Section titled “Next steps”