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docs/user/develop/basic/tool.md

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+# Build a tool
+
+English | [中文](tool.zh.md)
+
+A tool is a capability the model can call. This guide builds one with `defineTool`.
+
+## Minimal example
+
+```ts
+import type { Context } from 'cordis'
+import { defineTool } from '@deepseek-ai/dsh-tools'
+
+export const name = 'my-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' },
+    },
+    async execute(args) {
+      // args is inferred as { name: string }.
+      return [{ type: 'text', text: `Hello, ${args.name}!` }]
+    },
+  }))
+}
+```
+
+## Parameter definitions
+
+`parameters` uses a compact format that the framework converts to the JSON Schema sent to the model.
+
+### Primitive types
+
+```ts
+export const parameters = {
+  path: { type: 'string', required: true },
+  limit: { type: 'number' },
+  recursive: { type: 'boolean' },
+}
+// Inferred type: { path: string; limit?: number; recursive?: boolean }
+```
+
+### Enums
+
+```ts
+export const parameters = {
+  mode: { type: 'string', required: true, enum: ['read', 'write', 'append'] },
+}
+// Inferred type: { mode: string } (enum values are validated at runtime)
+```
+
+### Nested objects
+
+```ts
+export const parameters = {
+  options: {
+    type: 'object',
+    properties: {
+      timeout: { type: 'number' },
+      retries: { type: 'number' },
+    },
+  },
+}
+// Inferred type: { options?: { timeout?: number; retries?: number } }
+```
+
+### Arrays
+
+```ts
+export const parameters = {
+  tags: {
+    type: 'array',
+    items: { type: 'string' },
+  },
+}
+// Inferred type: { tags?: string[] }
+```
+
+### Property fields
+
+| Field | Type | Meaning |
+|------|------|------|
+| `type` | `'string' \| 'number' \| 'boolean' \| 'object' \| 'array'` | Value type |
+| `required` | `true` | Marks the property required and affects inference |
+| `description` | `string` | Description sent to the model |
+| `enum` | `string[]` | Allowed string values |
+| `properties` | `SchemaSpec` | Nested properties for an object |
+| `items` | `SchemaProp` | Element schema for an array |
+
+## The execute function
+
+`execute` receives validated, inferred `args` and an `exec` execution context:
+
+```ts
+import { defineTool } from '@deepseek-ai/dsh-tools'
+
+export const tool = defineTool({
+  name: 'example',
+  description: 'Return an example result.',
+  parameters: {},
+  async execute(args, exec) {
+    // args: inferred from parameters
+    // exec: ToolExecution context
+
+    // Return a ContentBlock array.
+    void args
+    void exec
+    return [{ type: 'text', text: 'result here' }]
+  },
+})
+```
+
+### Return value
+
+`execute` returns a `ContentBlock[]` that becomes the tool result visible to the model:
+
+```ts ignore-check
+// Text result
+return [{ type: 'text', text: 'file content here...' }]
+
+// Multiple blocks
+return [
+  { type: 'text', text: 'Found 3 matches:' },
+  { type: 'text', text: matchResults.join('\n') },
+]
+```
+
+### Argument validation
+
+Before calling `execute`, `defineTool` validates model-generated arguments. Invalid input raises `ToolArgsError`; the framework turns it into an `isError` result so the model can correct its call.
+
+Do not repeat type validation inside `execute`.
+
+## Presentation
+
+A tool can define UI presentation methods for terminal and ACP clients:
+
+```ts ignore-check
+defineTool({
+  name: 'bash',
+  // ...
+  presentCall(args) {
+    return {
+      card: 'terminal',
+      title: args.command,
+    }
+  },
+  presentResult(args, result) {
+    return {
+      card: 'terminal',
+      output: result.content.map(b => b.type === 'text' ? b.text : '').join(''),
+    }
+  },
+})
+```
+
+`presentCall` and `presentResult` are **pure functions**. Streaming UI and session replay may call them more than once.
+
+## Registration and unloading
+
+`ctx.tools.register()` returns a disposer, but a registration made through `ctx` is already tracked by the framework. Unloading the plugin removes the tool automatically, so the plugin does not call the disposer itself.
+
+```ts ignore-check
+// This is sufficient:
+ctx.tools.register(defineTool({ /* ... */ }))
+
+// No saved disposer or extra cleanup registration is needed.
+```
+
+## Complete example
+
+This tool counts files in a directory:
+
+```ts
+import type { Context } from 'cordis'
+import { defineTool } from '@deepseek-ai/dsh-tools'
+import { readdir } from 'node:fs/promises'
+
+export const name = 'file-counter'
+export const inject = ['tools']
+
+export function apply(ctx: Context) {
+  ctx.tools.register(defineTool({
+    name: 'count_files',
+    description: 'Count files in a directory.',
+    parameters: {
+      path: { type: 'string', required: true, description: 'Directory path' },
+      extension: { type: 'string', description: 'Filter by extension (e.g. ".ts")' },
+    },
+    async execute(args) {
+      const entries = await readdir(args.path, { withFileTypes: true })
+      let files = entries.filter(e => e.isFile())
+      if (args.extension) {
+        files = files.filter(f => f.name.endsWith(args.extension!))
+      }
+      return [{ type: 'text', text: `Found ${files.length} files.` }]
+    },
+  }))
+}
+```
+
+## Next steps
+
+- [Plugin configuration](./config.md) — make the tool configurable
+- [Capability layering](../practice/) — understand the interface/implementation/consumer pattern