HostedToolSearchTool with DeferredTools in the type by jozkee · Pull Request #7471 · dotnet/extensions

jozkee · 2026-04-16T17:37:38Z

Alternative to #7377.

Propose HostedToolSearchTool with the tools specified in the type as an IList<string>? DeferredTools.

This should allow us to nicely support MCP servers too by shoving the Server Name in the lists.
We lose the ability to specify defer_loading with a decorator, defer_loading is really not important for local tool search since returned tools are better not included at all until tool search finds it.
Namespace grouping would be handled by passing multiple HostedToolSearchTools. That seems like a rough edge but not terrible, I'm wondering if it would be better to wait until we have a built-in NamespaceTool.

Microsoft Reviewers: Open in CodeFlow

…r tool search support Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

…rredTools/NonDeferredTools - Redesign HostedToolSearchTool with DeferredTools/NonDeferredTools properties - Remove SearchableAIFunctionDeclaration (no longer needed) - Revert DelegatingAIFunctionDeclaration to internal - Update OpenAI provider: use HostedToolSearchTool enable/disable logic for defer_loading - Add ChatOptions parameter to AsOpenAIResponseTool extension method - Use AOT-safe ModelReaderWriter.Read with OpenAIContext.Default - Update API baselines and tests Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

…tor ToResponseTool signature - Fix O(N²) by finding HostedToolSearchTool once before the tools loop instead of scanning the list for each tool - Remove HostedToolSearchTool from json baseline (experimental types don't need entries) - Refactor ToResponseTool(AITool, ...) to take HostedToolSearchTool? directly instead of extracting from ChatOptions each time - Remove FindToolSearchTool helper method (inlined into callers) Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

…SearchTool private Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

…ation test Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

…s/NonDeferredTools from HostedToolSearchTool Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/extensions/sessions/7a29d49e-c422-4fe7-81f4-366bd781b460

…ai-dotnet#1053 comment, add DeferLoadingTools to HostedMcpServerTool Agent-Logs-Url: https://github.com/dotnet/extensions/sessions/08f652ed-169c-43c3-a247-829ebd0b3e4f Co-authored-by: jozkee <16040868+jozkee@users.noreply.github.com>

…gTools from HostedMcpServerTool, add interaction tests - Remove Namespace property and namespaceName parameter from SearchableAIFunctionDeclaration - Remove DeferLoadingTools property from HostedMcpServerTool - Update OpenAIResponsesChatClient to drop namespace patching and MCP defer_loading patching - Update RemoteMCP_DeferLoadingTools integration test to use AsOpenAIResponseTool() + Patch.Set + AsAITool() - Add tool_search_call/tool_search_output assertions to integration test - Add SearchableAIFunctionDeclaration + ApprovalRequiredAIFunction interaction tests - Add FunctionInvokingChatClient test for approval detection through searchable wrapper Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Remove [Experimental(AIToolSearch)] attribute from DelegatingAIFunctionDeclaration, SearchableAIFunctionDeclaration, and HostedToolSearchTool. Remove the AIToolSearch diagnostic constant from DiagnosticIds. Add API baseline entries for all three types in Microsoft.Extensions.AI.Abstractions.json. Clean up unused usings. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add tests verifying that the OpenAI API returns HTTP 400 when HostedToolSearchTool is used without any deferred tools: - UseToolSearch_OnlyToolSearchNoFunctions - UseToolSearch_WithNonDeferredFunctionsOnly Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…arch-support # Conflicts: # src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json

…e grouping in OpenAIResponsesChatClient - Add Namespace property and namespaceName parameter to SearchableAIFunctionDeclaration - Add namespaceName parameter to CreateToolSet for bulk namespace assignment - Add namespace grouping logic in OpenAIResponsesChatClient tools loop - Add ToNamespaceResponseTool helper using ModelReaderWriter for AOT-safe JSON - Add namespace unit tests in SearchableAIFunctionDeclarationTests - Add namespace VerbatimHttpHandler tests in OpenAIResponseClientTests - Add UseToolSearch_WithNamespace integration test with tool_search assertions - Add tool_search_call/tool_search_output assertions to existing integration test - Update API baseline Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…rouping from OpenAI provider Agent-Logs-Url: https://github.com/dotnet/extensions/sessions/a0e8d299-9f73-4db3-be63-674f590aa717 Co-authored-by: jozkee <16040868+jozkee@users.noreply.github.com>

…espace grouping from OpenAI provider" This reverts commit 89d8df4. Co-authored-by: jozkee <16040868+jozkee@users.noreply.github.com>

@namespace

… and restore @namespace param name Agent-Logs-Url: https://github.com/dotnet/extensions/sessions/1783bbad-9689-4b08-bfcc-79988248c2ff Co-authored-by: jozkee <16040868+jozkee@users.noreply.github.com>

- Replace per-tool SearchableAIFunctionDeclaration with collections-based DeferredTools and Namespace properties on HostedToolSearchTool - Support multiple HostedToolSearchTool instances with different/same namespaces (same namespace merges, first-claims wins) - Patch defer_loading on both FunctionTool and McpTool when claimed by a HostedToolSearchTool - Group deferred FunctionTool and McpTool into namespace containers - Widen ToNamespaceResponseTool to accept any ResponseTool - Add AsOpenAIResponseTool ChatOptions parameter for defer context - Delete SearchableAIFunctionDeclaration and its tests - Make DelegatingAIFunctionDeclaration internal (no external consumers) - Add conversion, VerbatimHttpHandler, and integration tests Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Adds a revised “tool_search” implementation for OpenAI Responses that enables deferred tool loading and optional namespace grouping via a new HostedToolSearchTool abstraction, with extensive unit/integration test coverage.

Changes:

Introduces HostedToolSearchTool with IList<string>? DeferredTools and optional Namespace for grouping deferred tools.
Updates OpenAI Responses tool conversion to emit tool_search, patch defer_loading, and wrap deferred tools in {"type":"namespace"} containers when configured.
Expands unit/integration tests to validate request JSON and runtime behavior for deferred loading, namespaces, and MCP scenarios.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/Libraries/Microsoft.Extensions.AI.OpenAI.Tests/OpenAIResponseClientTests.cs	Adds VerbatimHttpHandler request-shape tests covering tool_search, deferred loading, namespaces, and MCP grouping.
test/Libraries/Microsoft.Extensions.AI.OpenAI.Tests/OpenAIResponseClientIntegrationTests.cs	Adds live integration coverage for tool_search behavior (including MCP + RawRepresentation assertions).
test/Libraries/Microsoft.Extensions.AI.OpenAI.Tests/OpenAIConversionTests.cs	Adds conversion tests for tool_search emission and defer-loading patching based on `ChatOptions`.
test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Tools/HostedToolSearchToolTests.cs	Adds basic round-trip tests for `HostedToolSearchTool` properties.
src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs	Implements `HostedToolSearchTool` conversion + defer-loading patching + namespace tool container construction.
src/Libraries/Microsoft.Extensions.AI.OpenAI/MicrosoftExtensionsAIResponsesExtensions.cs	Extends `AsOpenAIResponseTool(AITool)` to accept optional `ChatOptions` for conversion context.
src/Libraries/Microsoft.Extensions.AI.OpenAI/Microsoft.Extensions.AI.OpenAI.json	Updates API contract for the changed extension method signature (optional `ChatOptions`).
src/Libraries/Microsoft.Extensions.AI.Abstractions/Tools/HostedToolSearchTool.cs	Adds the new marker tool type and public surface (`DeferredTools`, `Namespace`).
src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json	Adds the new public API surface for `HostedToolSearchTool`.

Copilot · 2026-04-16T17:44:35Z

+/// By default, when a <see cref="HostedToolSearchTool"/> is present in the tools list, all other tools are treated
+/// as having deferred loading enabled. Use <see cref="DeferredTools"/> to control which tools have deferred loading
+/// on a per-tool basis.


The remarks say that when HostedToolSearchTool is present “all other tools are treated as having deferred loading enabled”, but the provider logic only applies defer_loading to function tools and MCP server tools (hosted tools like web_search aren’t deferred). Consider tightening the wording to “all function/MCP tools (or all tools that support deferred loading)” to avoid misleading API docs.

Copilot · 2026-04-16T17:44:35Z

+    /// When non-null, all deferred function tools are wrapped inside a <c>{"type":"namespace","name":"..."}</c>
+    /// container. Non-deferred tools remain as top-level tools.
+    /// </para>
+    /// <para>
+    /// When <see langword="null"/> (the default), deferred tools are sent as top-level function tools


The Namespace property remarks say “all deferred function tools are wrapped” but the OpenAI provider also namespaces deferred MCP server tools (see McpToolNamespaceGrouping tests / responseTool is McpTool branch). Update the docs to include MCP tools (or more generally “deferred tools”) so behavior matches the documentation.

Suggested change

/// When non-null, all deferred function tools are wrapped inside a <c>{"type":"namespace","name":"..."}</c>

/// container. Non-deferred tools remain as top-level tools.

/// </para>

/// <para>

/// When <see langword="null"/> (the default), deferred tools are sent as top-level function tools

/// When non-null, all deferred tools are wrapped inside a <c>{"type":"namespace","name":"..."}</c>

/// container. Non-deferred tools remain as top-level tools.

/// </para>

/// <para>

/// When <see langword="null"/> (the default), deferred tools are sent as top-level tools

Copilot · 2026-04-16T17:44:36Z

+    /// <summary>Checks whether any <see cref="HostedToolSearchTool"/> in the options considers the tool deferred.</summary>
+    private static bool IsDeferredByAnyToolSearch(string toolName, ChatOptions? options)
+    {
+        if (options?.Tools is { } tools)
+        {
+            foreach (AITool t in tools)
+            {
+                if (t is HostedToolSearchTool toolSearch && IsDeferredLoading(toolName, toolSearch))
+                {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }


The deferred-loading / namespace lookup currently scans options.Tools repeatedly (IsDeferredByAnyToolSearch loops tools for every function/MCP tool, and FindNamespaceForTool loops tools again for each tool during request construction), making tool processing O(n²). Consider precomputing a lookup (e.g., HashSet of deferred tool names + toolName→namespace map) once per request to reduce overhead and simplify the control flow.

Copilot AI and others added 20 commits April 3, 2026 14:37

Implement HostedToolSearchTool and SearchableAIFunctionDeclaration fo…

475d067

…r tool search support Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Extract shared FindToolSearchTool helper to deduplicate lookup code

40f3432

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Simplify ToResponseTool: add ChatOptions-only overload, make FindTool…

5997a6a

…SearchTool private Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Add unit tests for HostedToolSearchTool JSON serialization and integr…

7f3893f

…ation test Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Update tests

2b39eb9

revert namespace param rename

78f7d57

Merge remote-tracking branch 'upstream/main' into copilot/add-tool-se…

1822466

…arch-support # Conflicts: # src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json

Feedback

ba60cd3

Remove Namespace from SearchableAIFunctionDeclaration and namespace g…

89d8df4

…rouping from OpenAI provider Agent-Logs-Url: https://github.com/dotnet/extensions/sessions/a0e8d299-9f73-4db3-be63-674f590aa717 Co-authored-by: jozkee <16040868+jozkee@users.noreply.github.com>

Revert "Remove Namespace from SearchableAIFunctionDeclaration and nam…

0579b05

…espace grouping from OpenAI provider" This reverts commit 89d8df4. Co-authored-by: jozkee <16040868+jozkee@users.noreply.github.com>

Fix CI: replace KeyValuePair deconstruction for net462/netstandard2.0…

3a28bd0

… and restore @namespace param name Agent-Logs-Url: https://github.com/dotnet/extensions/sessions/1783bbad-9689-4b08-bfcc-79988248c2ff Co-authored-by: jozkee <16040868+jozkee@users.noreply.github.com>

jozkee requested a review from a team as a code owner April 16, 2026 17:37

Copilot AI review requested due to automatic review settings April 16, 2026 17:37

github-actions bot added the area-ai Microsoft.Extensions.AI libraries label Apr 16, 2026

jozkee changed the title ~~Copilot/tool search v2~~ HostedToolSearchTool with DeferredTools in the type Apr 16, 2026

dotnet-policy-service bot assigned jozkee Apr 16, 2026

Copilot started reviewing on behalf of jozkee April 16, 2026 17:38 View session

jozkee mentioned this pull request Apr 16, 2026

Add HostedToolSearchTool and SearchableAIFunctionDeclaration for tool search / deferred loading support #7377

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HostedToolSearchTool with DeferredTools in the type#7471

HostedToolSearchTool with DeferredTools in the type#7471
jozkee wants to merge 20 commits intomainfrom
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