diff --git a/src/Contracts/ProviderInterface.php b/src/Contracts/ProviderInterface.php
index 3e12c9b..d88f3a5 100644
--- a/src/Contracts/ProviderInterface.php
+++ b/src/Contracts/ProviderInterface.php
@@ -23,6 +23,22 @@
  *
  * Every AI provider (Anthropic, OpenAI, etc.) must implement this interface
  * to participate in the PapiAI ecosystem. Handles both synchronous and streaming chat.
+ *
+ * The chat options bag is defined once here as a reusable Psalm type; providers import it with
+ * `@psalm-import-type ChatOptions from ProviderInterface` so a new option never drifts across
+ * per-provider docblocks. `toolChoice` forces the answer channel: "auto" (the default when absent),
+ * "none", "required", or `["name" => "<tool>"]` to force a specific tool. Providers validate it
+ * (see PapiAI\Core\ToolChoice) and throw before any HTTP call when it cannot be met.
+ *
+ * @psalm-type ChatOptions = array{
+ *     model?: string,
+ *     tools?: array,
+ *     maxTokens?: int,
+ *     temperature?: float,
+ *     stopSequences?: array<string>,
+ *     outputSchema?: array,
+ *     toolChoice?: string|array{name: string},
+ * }
  */
 interface ProviderInterface
 {
@@ -30,14 +46,7 @@ interface ProviderInterface
      * Send a chat completion request.
      *
      * @param array<Message> $messages The conversation messages
-     * @param array{
-     *     model?: string,
-     *     tools?: array,
-     *     maxTokens?: int,
-     *     temperature?: float,
-     *     stopSequences?: array<string>,
-     *     outputSchema?: array,
-     * } $options Request options
+     * @param ChatOptions    $options  Request options (see the class docblock, incl. toolChoice)
      *
      * @return Response The completed response with text, tool calls, and usage stats
      */
diff --git a/src/ToolChoice.php b/src/ToolChoice.php
new file mode 100644
index 0000000..fdde4f4
--- /dev/null
+++ b/src/ToolChoice.php
@@ -0,0 +1,138 @@
+<?php
+
+/*
+ * This file is part of PapiAI,
+ * A simple but powerful PHP library for building AI agents.
+ *
+ * (c) Marcello Duarte <marcello.duarte@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace PapiAI\Core;
+
+use InvalidArgumentException;
+
+/**
+ * Normalised, validated representation of the provider-agnostic `toolChoice` option.
+ *
+ * Callers pass `toolChoice` to a provider's chat() as one of:
+ *   - `'auto'`      the model decides (the default when the option is absent)
+ *   - `'none'`      the model must not call tools
+ *   - `'required'`  the model must call one of the declared tools
+ *   - `['name' => '<tool>']`  the model must call exactly that tool
+ *
+ * Each provider calls {@see self::fromOption()} to validate the value against the declared tools
+ * (failing loudly, before any HTTP call) and then maps the normalised `mode`/`toolName` to its own
+ * API mechanism. Keeping validation here guarantees identical semantics across every provider.
+ */
+final class ToolChoice
+{
+    public const AUTO = 'auto';
+    public const NONE = 'none';
+    public const REQUIRED = 'required';
+
+    /**
+     * @param string      $mode     One of AUTO, NONE, REQUIRED
+     * @param string|null $toolName The specific tool to force, when the caller named one
+     */
+    private function __construct(
+        public readonly string $mode,
+        public readonly ?string $toolName = null,
+    ) {
+    }
+
+    /**
+     * Validate and normalise a raw `toolChoice` option against the declared tools.
+     *
+     * @param string|array<string, mixed>       $value The raw toolChoice option
+     * @param array<int, array<string, mixed>>  $tools The declared tool definitions (each with a `name`)
+     *
+     * @throws InvalidArgumentException On an unknown value; on `none`/`required`/specific with no tools
+     *   declared; or when a named tool is not among the declared tools
+     */
+    public static function fromOption(string|array $value, array $tools): self
+    {
+        if (is_string($value)) {
+            if (!in_array($value, [self::AUTO, self::NONE, self::REQUIRED], true)) {
+                throw new InvalidArgumentException(sprintf(
+                    'Unknown toolChoice "%s". Expected "auto", "none", "required", or ["name" => "<tool>"].',
+                    $value,
+                ));
+            }
+
+            $mode = $value;
+            $toolName = null;
+        } else {
+            $name = $value['name'] ?? null;
+            if (!is_string($name) || $name === '') {
+                throw new InvalidArgumentException('Invalid toolChoice array. Expected ["name" => "<tool>"].');
+            }
+
+            $mode = self::REQUIRED;
+            $toolName = $name;
+        }
+
+        if ($mode !== self::AUTO && $tools === []) {
+            throw new InvalidArgumentException(sprintf(
+                'toolChoice "%s" requires at least one declared tool, but none were provided.',
+                $toolName ?? $mode,
+            ));
+        }
+
+        if ($toolName !== null) {
+            $names = self::toolNames($tools);
+            if (!in_array($toolName, $names, true)) {
+                throw new InvalidArgumentException(sprintf(
+                    'toolChoice names tool "%s", which is not among the declared tools (%s).',
+                    $toolName,
+                    $names === [] ? 'none' : implode(', ', $names),
+                ));
+            }
+        }
+
+        return new self($mode, $toolName);
+    }
+
+    /**
+     * Whether this is the default, model-decides choice.
+     *
+     * @return bool True for auto with no forced tool
+     */
+    public function isAuto(): bool
+    {
+        return $this->mode === self::AUTO && $this->toolName === null;
+    }
+
+    /**
+     * Whether a specific tool is being forced.
+     *
+     * @return bool True when a tool name was given
+     */
+    public function forcesSpecificTool(): bool
+    {
+        return $this->toolName !== null;
+    }
+
+    /**
+     * Extract the declared tool names.
+     *
+     * @param array<int, array<string, mixed>> $tools
+     *
+     * @return list<string>
+     */
+    private static function toolNames(array $tools): array
+    {
+        $names = [];
+        foreach ($tools as $tool) {
+            if (isset($tool['name']) && is_string($tool['name'])) {
+                $names[] = $tool['name'];
+            }
+        }
+
+        return $names;
+    }
+}
diff --git a/tests/Unit/ToolChoiceTest.php b/tests/Unit/ToolChoiceTest.php
new file mode 100644
index 0000000..4b31673
--- /dev/null
+++ b/tests/Unit/ToolChoiceTest.php
@@ -0,0 +1,75 @@
+<?php
+
+declare(strict_types=1);
+
+use PapiAI\Core\ToolChoice;
+
+$tools = [
+    ['name' => 'get_weather', 'description' => 'Weather', 'parameters' => []],
+    ['name' => 'search', 'description' => 'Search', 'parameters' => []],
+];
+
+describe('ToolChoice', function () use ($tools) {
+    it('normalises auto', function () {
+        $choice = ToolChoice::fromOption('auto', []);
+
+        expect($choice->mode)->toBe(ToolChoice::AUTO);
+        expect($choice->toolName)->toBeNull();
+        expect($choice->isAuto())->toBeTrue();
+        expect($choice->forcesSpecificTool())->toBeFalse();
+    });
+
+    it('normalises none', function () use ($tools) {
+        expect(ToolChoice::fromOption('none', $tools)->mode)->toBe(ToolChoice::NONE);
+    });
+
+    it('normalises required', function () use ($tools) {
+        $choice = ToolChoice::fromOption('required', $tools);
+
+        expect($choice->mode)->toBe(ToolChoice::REQUIRED);
+        expect($choice->toolName)->toBeNull();
+        expect($choice->forcesSpecificTool())->toBeFalse();
+    });
+
+    it('normalises a specific tool to required + name', function () use ($tools) {
+        $choice = ToolChoice::fromOption(['name' => 'search'], $tools);
+
+        expect($choice->mode)->toBe(ToolChoice::REQUIRED);
+        expect($choice->toolName)->toBe('search');
+        expect($choice->forcesSpecificTool())->toBeTrue();
+    });
+
+    describe('validation (fails loud, before any HTTP)', function () use ($tools) {
+        it('rejects an unknown string value', function () use ($tools) {
+            expect(fn () => ToolChoice::fromOption('always', $tools))
+                ->toThrow(InvalidArgumentException::class, 'Unknown toolChoice');
+        });
+
+        it('rejects a malformed array', function () use ($tools) {
+            expect(fn () => ToolChoice::fromOption(['tool' => 'search'], $tools))
+                ->toThrow(InvalidArgumentException::class, 'Invalid toolChoice array');
+            expect(fn () => ToolChoice::fromOption(['name' => ''], $tools))
+                ->toThrow(InvalidArgumentException::class);
+        });
+
+        it('rejects required with no tools declared', function () {
+            expect(fn () => ToolChoice::fromOption('required', []))
+                ->toThrow(InvalidArgumentException::class, 'requires at least one declared tool');
+        });
+
+        it('rejects none with no tools declared', function () {
+            expect(fn () => ToolChoice::fromOption('none', []))
+                ->toThrow(InvalidArgumentException::class, 'requires at least one declared tool');
+        });
+
+        it('rejects a specific tool with no tools declared', function () {
+            expect(fn () => ToolChoice::fromOption(['name' => 'search'], []))
+                ->toThrow(InvalidArgumentException::class);
+        });
+
+        it('rejects a specific tool name not among the declared tools', function () use ($tools) {
+            expect(fn () => ToolChoice::fromOption(['name' => 'unknown_tool'], $tools))
+                ->toThrow(InvalidArgumentException::class, 'not among the declared tools');
+        });
+    });
+});