From af21430853086d8656e7c4707275821687772baa Mon Sep 17 00:00:00 2001
From: Sophia <niannian1054@gmail.com>
Date: Thu, 14 Aug 2025 16:54:46 -0700
Subject: [PATCH 1/2] feat: add tool choice and parallel tool calls control

- Implement provider-specific tool choice handling
- Add InvalidToolChoiceError for validation
- Enhance tool execution flow to prevent infinite loops with non-auto choices
---
 lib/ruby_llm/chat.rb                      | 44 +++++++++++++++++++----
 lib/ruby_llm/error.rb                     |  1 +
 lib/ruby_llm/provider.rb                  |  7 +++-
 lib/ruby_llm/providers/anthropic/chat.rb  | 15 +++++---
 lib/ruby_llm/providers/anthropic/tools.rb |  9 +++++
 lib/ruby_llm/providers/bedrock/chat.rb    |  8 +++--
 lib/ruby_llm/providers/gemini/chat.rb     | 12 +++++--
 lib/ruby_llm/providers/gemini/tools.rb    | 15 ++++++++
 lib/ruby_llm/providers/mistral/chat.rb    |  3 +-
 lib/ruby_llm/providers/openai/chat.rb     | 11 ++++--
 lib/ruby_llm/providers/openai/tools.rb    | 16 +++++++++
 11 files changed, 122 insertions(+), 19 deletions(-)

diff --git a/lib/ruby_llm/chat.rb b/lib/ruby_llm/chat.rb
index 7131aeb7..f9ec5150 100644
--- a/lib/ruby_llm/chat.rb
+++ b/lib/ruby_llm/chat.rb
@@ -11,7 +11,7 @@ module RubyLLM
   class Chat
     include Enumerable
 
-    attr_reader :model, :messages, :tools, :params, :headers, :schema
+    attr_reader :model, :messages, :tools, :tool_choice, :parallel_tool_calls, :params, :headers, :schema
 
     def initialize(model: nil, provider: nil, assume_model_exists: false, context: nil)
       if assume_model_exists && !provider
@@ -23,6 +23,8 @@ def initialize(model: nil, provider: nil, assume_model_exists: false, context: n
       model_id = model || @config.default_model
       with_model(model_id, provider: provider, assume_exists: assume_model_exists)
       @temperature = 0.7
+      @tool_choice = nil
+      @parallel_tool_calls = nil
       @messages = []
       @tools = {}
       @params = {}
@@ -50,15 +52,19 @@ def with_instructions(instructions, replace: false)
       self
     end
 
-    def with_tool(tool)
-      tool_instance = tool.is_a?(Class) ? tool.new : tool
-      @tools[tool_instance.name.to_sym] = tool_instance
+    def with_tool(tool, choice: nil, parallel: nil)
+      unless tool.nil?
+        tool_instance = tool.is_a?(Class) ? tool.new : tool
+        @tools[tool_instance.name.to_sym] = tool_instance
+      end
+      update_tool_options(choice:, parallel:)
       self
     end
 
-    def with_tools(*tools, replace: false)
+    def with_tools(*tools, replace: false, choice: nil, parallel: nil)
       @tools.clear if replace
       tools.compact.each { |tool| with_tool tool }
+      update_tool_options(choice:, parallel:)
       self
     end
 
@@ -136,6 +142,8 @@ def complete(&) # rubocop:disable Metrics/PerceivedComplexity
         params: @params,
         headers: @headers,
         schema: @schema,
+        tool_choice: @tool_choice,
+        parallel_tool_calls: @parallel_tool_calls,
         &wrap_streaming_block(&)
       )
 
@@ -189,7 +197,7 @@ def wrap_streaming_block(&block)
       end
     end
 
-    def handle_tool_calls(response, &)
+    def handle_tool_calls(response, &) # rubocop:disable Metrics/PerceivedComplexity
       halt_result = nil
 
       response.tool_calls.each_value do |tool_call|
@@ -203,7 +211,9 @@ def handle_tool_calls(response, &)
         halt_result = result if result.is_a?(Tool::Halt)
       end
 
-      halt_result || complete(&)
+      return halt_result if halt_result
+
+      should_continue_after_tools? ? complete(&) : response
     end
 
     def execute_tool(tool_call)
@@ -212,6 +222,26 @@ def execute_tool(tool_call)
       tool.call(args)
     end
 
+    def update_tool_options(choice:, parallel:)
+      unless choice.nil?
+        valid_tool_choices = %i[auto none any] + tools.keys
+        unless valid_tool_choices.include?(choice.to_sym)
+          raise InvalidToolChoiceError,
+                "Invalid tool choice: #{choice}. Valid choices are: #{valid_tool_choices.join(', ')}"
+        end
+
+        @tool_choice = choice.to_sym
+      end
+
+      @parallel_tool_calls = !!parallel unless parallel.nil?
+    end
+
+    def should_continue_after_tools?
+      # Continue conversation only with :auto tool choice to avoid infinite loops.
+      # With :any or specific tool choices, the model would keep calling tools repeatedly.
+      tool_choice.nil? || tool_choice == :auto
+    end
+
     def instance_variables
       super - %i[@connection @config]
     end
diff --git a/lib/ruby_llm/error.rb b/lib/ruby_llm/error.rb
index 1bcc018b..a20fa0f2 100644
--- a/lib/ruby_llm/error.rb
+++ b/lib/ruby_llm/error.rb
@@ -22,6 +22,7 @@ def initialize(response = nil, message = nil)
   # Error classes for non-HTTP errors
   class ConfigurationError < StandardError; end
   class InvalidRoleError < StandardError; end
+  class InvalidToolChoiceError < StandardError; end
   class ModelNotFoundError < StandardError; end
   class UnsupportedAttachmentError < StandardError; end
 
diff --git a/lib/ruby_llm/provider.rb b/lib/ruby_llm/provider.rb
index ed0c2ac8..be8c3127 100644
--- a/lib/ruby_llm/provider.rb
+++ b/lib/ruby_llm/provider.rb
@@ -40,7 +40,9 @@ def configuration_requirements
       self.class.configuration_requirements
     end
 
-    def complete(messages, tools:, temperature:, model:, params: {}, headers: {}, schema: nil, &) # rubocop:disable Metrics/ParameterLists
+    # rubocop:disable Metrics/ParameterLists
+    def complete(messages, tools:, temperature:, model:, params: {}, headers: {}, schema: nil,
+                 tool_choice: nil, parallel_tool_calls: nil, &)
       normalized_temperature = maybe_normalize_temperature(temperature, model)
 
       payload = Utils.deep_merge(
@@ -48,6 +50,8 @@ def complete(messages, tools:, temperature:, model:, params: {}, headers: {}, sc
         render_payload(
           messages,
           tools: tools,
+          tool_choice: tool_choice,
+          parallel_tool_calls: parallel_tool_calls,
           temperature: normalized_temperature,
           model: model,
           stream: block_given?,
@@ -61,6 +65,7 @@ def complete(messages, tools:, temperature:, model:, params: {}, headers: {}, sc
         sync_response @connection, payload, headers
       end
     end
+    # rubocop:enable Metrics/ParameterLists
 
     def list_models
       response = @connection.get models_url
diff --git a/lib/ruby_llm/providers/anthropic/chat.rb b/lib/ruby_llm/providers/anthropic/chat.rb
index 64cd764b..cbc0db92 100644
--- a/lib/ruby_llm/providers/anthropic/chat.rb
+++ b/lib/ruby_llm/providers/anthropic/chat.rb
@@ -11,14 +11,17 @@ def completion_url
           '/v1/messages'
         end
 
-        def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil) # rubocop:disable Metrics/ParameterLists,Lint/UnusedMethodArgument
+        # rubocop:disable Metrics/ParameterLists,Lint/UnusedMethodArgument
+        def render_payload(messages, tools:, tool_choice:, parallel_tool_calls:,
+                           temperature:, model:, stream: false, schema: nil)
           system_messages, chat_messages = separate_messages(messages)
           system_content = build_system_content(system_messages)
 
           build_base_payload(chat_messages, model, stream).tap do |payload|
-            add_optional_fields(payload, system_content:, tools:, temperature:)
+            add_optional_fields(payload, system_content:, tools:, tool_choice:, parallel_tool_calls:, temperature:)
           end
         end
+        # rubocop:enable Metrics/ParameterLists,Lint/UnusedMethodArgument
 
         def separate_messages(messages)
           messages.partition { |msg| msg.role == :system }
@@ -44,8 +47,12 @@ def build_base_payload(chat_messages, model, stream)
           }
         end
 
-        def add_optional_fields(payload, system_content:, tools:, temperature:)
-          payload[:tools] = tools.values.map { |t| Tools.function_for(t) } if tools.any?
+        def add_optional_fields(payload, system_content:, tools:, tool_choice:, parallel_tool_calls:, temperature:) # rubocop:disable Metrics/ParameterLists
+          if tools.any?
+            payload[:tools] = tools.values.map { |t| Tools.function_for(t) }
+            payload[:tool_choice] = build_tool_choice(tool_choice, parallel_tool_calls) unless tool_choice.nil?
+          end
+
           payload[:system] = system_content unless system_content.empty?
           payload[:temperature] = temperature unless temperature.nil?
         end
diff --git a/lib/ruby_llm/providers/anthropic/tools.rb b/lib/ruby_llm/providers/anthropic/tools.rb
index 0b4d1c7c..8f26cb79 100644
--- a/lib/ruby_llm/providers/anthropic/tools.rb
+++ b/lib/ruby_llm/providers/anthropic/tools.rb
@@ -102,6 +102,15 @@ def clean_parameters(parameters)
         def required_parameters(parameters)
           parameters.select { |_, param| param.required }.keys
         end
+
+        def build_tool_choice(tool_choice, parallel_tool_calls)
+          {
+            type: %i[auto any none].include?(tool_choice) ? tool_choice : :tool
+          }.tap do |tc|
+            tc[:name] = tool_choice if tc[:type] == :tool
+            tc[:disable_parallel_tool_use] = !parallel_tool_calls unless tc[:type] == :none || parallel_tool_calls.nil?
+          end
+        end
       end
     end
   end
diff --git a/lib/ruby_llm/providers/bedrock/chat.rb b/lib/ruby_llm/providers/bedrock/chat.rb
index 94655d11..a4d5220f 100644
--- a/lib/ruby_llm/providers/bedrock/chat.rb
+++ b/lib/ruby_llm/providers/bedrock/chat.rb
@@ -40,7 +40,9 @@ def completion_url
           "model/#{@model_id}/invoke"
         end
 
-        def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil) # rubocop:disable Lint/UnusedMethodArgument,Metrics/ParameterLists
+        # rubocop:disable Metrics/ParameterLists,Lint/UnusedMethodArgument
+        def render_payload(messages, tools:, tool_choice:, parallel_tool_calls:,
+                           temperature:, model:, stream: false, schema: nil)
           # Hold model_id in instance variable for use in completion_url and stream_url
           @model_id = model
 
@@ -48,9 +50,11 @@ def render_payload(messages, tools:, temperature:, model:, stream: false, schema
           system_content = Anthropic::Chat.build_system_content(system_messages)
 
           build_base_payload(chat_messages, model).tap do |payload|
-            Anthropic::Chat.add_optional_fields(payload, system_content:, tools:, temperature:)
+            Anthropic::Chat.add_optional_fields(payload, system_content:, tools:, tool_choice:,
+                                                         parallel_tool_calls:, temperature:)
           end
         end
+        # rubocop:enable Metrics/ParameterLists,Lint/UnusedMethodArgument
 
         def build_base_payload(chat_messages, model)
           {
diff --git a/lib/ruby_llm/providers/gemini/chat.rb b/lib/ruby_llm/providers/gemini/chat.rb
index 5254722a..d25dd8c2 100644
--- a/lib/ruby_llm/providers/gemini/chat.rb
+++ b/lib/ruby_llm/providers/gemini/chat.rb
@@ -11,7 +11,9 @@ def completion_url
           "models/#{@model}:generateContent"
         end
 
-        def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil) # rubocop:disable Metrics/ParameterLists,Lint/UnusedMethodArgument
+        # rubocop:disable Metrics/ParameterLists,Lint/UnusedMethodArgument
+        def render_payload(messages, tools:, tool_choice:, parallel_tool_calls:,
+                           temperature:, model:, stream: false, schema: nil)
           @model = model # Store model for completion_url/stream_url
           payload = {
             contents: format_messages(messages),
@@ -25,9 +27,15 @@ def render_payload(messages, tools:, temperature:, model:, stream: false, schema
             payload[:generationConfig][:responseSchema] = convert_schema_to_gemini(schema)
           end
 
-          payload[:tools] = format_tools(tools) if tools.any?
+          if tools.any?
+            payload[:tools] = format_tools(tools)
+            # Gemini doesn't support controlling parallel tool calls
+            payload[:toolConfig] = build_tool_config(tool_choice) unless tool_choice.nil?
+          end
+
           payload
         end
+        # rubocop:enable Metrics/ParameterLists,Lint/UnusedMethodArgument
 
         private
 
diff --git a/lib/ruby_llm/providers/gemini/tools.rb b/lib/ruby_llm/providers/gemini/tools.rb
index fd178d24..7a31a0a1 100644
--- a/lib/ruby_llm/providers/gemini/tools.rb
+++ b/lib/ruby_llm/providers/gemini/tools.rb
@@ -76,6 +76,21 @@ def param_type_for_gemini(type)
           else 'STRING'
           end
         end
+
+        def build_tool_config(tool_choice)
+          {
+            functionCallingConfig: {
+              mode: specific_tool_choice?(tool_choice) ? 'any' : tool_choice
+            }.tap do |config|
+              # Use allowedFunctionNames to simulate specific tool choice
+              config[:allowedFunctionNames] = [tool_choice] if specific_tool_choice?(tool_choice)
+            end
+          }
+        end
+
+        def specific_tool_choice?(tool_choice)
+          !%i[auto none any].include?(tool_choice)
+        end
       end
     end
   end
diff --git a/lib/ruby_llm/providers/mistral/chat.rb b/lib/ruby_llm/providers/mistral/chat.rb
index 74d508d1..c2a6321e 100644
--- a/lib/ruby_llm/providers/mistral/chat.rb
+++ b/lib/ruby_llm/providers/mistral/chat.rb
@@ -13,7 +13,8 @@ def format_role(role)
         end
 
         # rubocop:disable Metrics/ParameterLists
-        def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil)
+        def render_payload(messages, tools:, tool_choice:, parallel_tool_calls:, temperature:, model:, stream: false,
+                           schema: nil)
           payload = super
           # Mistral doesn't support stream_options
           payload.delete(:stream_options)
diff --git a/lib/ruby_llm/providers/openai/chat.rb b/lib/ruby_llm/providers/openai/chat.rb
index 9ed7e170..7d0a5fd6 100644
--- a/lib/ruby_llm/providers/openai/chat.rb
+++ b/lib/ruby_llm/providers/openai/chat.rb
@@ -11,7 +11,9 @@ def completion_url
 
         module_function
 
-        def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil) # rubocop:disable Metrics/ParameterLists
+        # rubocop:disable Metrics/ParameterLists
+        def render_payload(messages, tools:, tool_choice:, parallel_tool_calls:,
+                           temperature:, model:, stream: false, schema: nil)
           payload = {
             model: model,
             messages: format_messages(messages),
@@ -21,7 +23,11 @@ def render_payload(messages, tools:, temperature:, model:, stream: false, schema
           # Only include temperature if it's not nil (some models don't accept it)
           payload[:temperature] = temperature unless temperature.nil?
 
-          payload[:tools] = tools.map { |_, tool| tool_for(tool) } if tools.any?
+          if tools.any?
+            payload[:tools] = tools.map { |_, tool| tool_for(tool) }
+            payload[:tool_choice] = build_tool_choice(tool_choice) unless tool_choice.nil?
+            payload[:parallel_tool_calls] = parallel_tool_calls unless parallel_tool_calls.nil?
+          end
 
           if schema
             # Use strict mode from schema if specified, default to true
@@ -40,6 +46,7 @@ def render_payload(messages, tools:, temperature:, model:, stream: false, schema
           payload[:stream_options] = { include_usage: true } if stream
           payload
         end
+        # rubocop:enable Metrics/ParameterLists
 
         def parse_completion_response(response)
           data = response.body
diff --git a/lib/ruby_llm/providers/openai/tools.rb b/lib/ruby_llm/providers/openai/tools.rb
index e4b76c0c..7cf87d89 100644
--- a/lib/ruby_llm/providers/openai/tools.rb
+++ b/lib/ruby_llm/providers/openai/tools.rb
@@ -67,6 +67,22 @@ def parse_tool_calls(tool_calls, parse_arguments: true)
             ]
           end
         end
+
+        def build_tool_choice(tool_choice)
+          case tool_choice
+          when :auto, :none
+            tool_choice
+          when :any
+            :required
+          else
+            {
+              type: 'function',
+              function: {
+                name: tool_choice
+              }
+            }
+          end
+        end
       end
     end
   end

From 47923bce1257bad450cad69a012e51a726e04a8e Mon Sep 17 00:00:00 2001
From: Sophia <niannian1054@gmail.com>
Date: Thu, 14 Aug 2025 18:00:05 -0700
Subject: [PATCH 2/2] docs: add Tool Choice Control section to tools.md

---
 docs/_core_features/tools.md | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/docs/_core_features/tools.md b/docs/_core_features/tools.md
index aadb73f6..3e352804 100644
--- a/docs/_core_features/tools.md
+++ b/docs/_core_features/tools.md
@@ -136,6 +136,27 @@ puts response.content
 # => "Current weather at 52.52, 13.4: Temperature: 12.5°C, Wind Speed: 8.3 km/h, Conditions: Mainly clear, partly cloudy, and overcast."
 ```
 
+### Tool Choice Control
+
+Control when and how tools are called using `choice` and `parallel` options:
+
+```ruby
+chat = RubyLLM.chat(model: 'gpt-4o')
+
+# Choice options
+chat.with_tool(Weather, choice: :auto)    # Model decides whether to call any provided tools or not (default)
+chat.with_tool(Weather, choice: :any)     # Model must use one of the provided tools
+chat.with_tool(Weather, choice: :none)    # No tools
+chat.with_tool(Weather, choice: :weather) # Force specific tool
+
+# Parallel tool calls
+chat.with_tools(Weather, Calculator, parallel: true)  # Model can output multiple tool calls at once (default)
+chat.with_tools(Weather, Calculator, parallel: false) # At most one tool call
+```
+
+> With `:any` or specific tool choices, tool results are not automatically sent back to the AI model (see The Tool Execution Flow section below) to prevent infinite loops.
+{: .note }
+
 ### Model Compatibility
 {: .d-inline-block }