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.NET: Support Agent Skills by SergeyMenshykh · Pull Request #4122 · microsoft/agent-framework · GitHub
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.NET: Support Agent Skills - #4122

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SergeyMenshykh merged 19 commits into
microsoft:mainfrom
SergeyMenshykh:support-agent-skills
Feb 20, 2026
Merged

.NET: Support Agent Skills#4122
SergeyMenshykh merged 19 commits into
microsoft:mainfrom
SergeyMenshykh:support-agent-skills

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@SergeyMenshykh SergeyMenshykh commented Feb 20, 2026 •
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Summary

Adds FileAgentSkillsProvider, an AIContextProvider that discovers and exposes Agent Skills from filesystem directories following the Agent Skills specification progressive disclosure pattern: advertise → load → read resources.

Changes

  • FileAgentSkillsProvider — discovers SKILL.md files from configured directories, advertises skills via system prompt injection, and provides load_skill / read_skill_resource tools for on-demand access.
  • FileAgentSkillsProviderOptions — configuration for custom prompt templates.
  • FileAgentSkillLoader / FileAgentSkill / SkillFrontmatter — internal helpers and model classes for skill discovery, frontmatter parsing, and secure resource reading (path traversal / symlink guards).
  • Unit tests covering discovery, loading, resource reading, and security scenarios.
  • Sample (Agent_Step01_BasicSkills) demonstrating usage with an expense-report skill.
  • FileAgentSkillsProvider is marked as experimental (MAAI001) using DiagnosticIds.

Key Design Decisions

  • Skills are read-only static content; no code execution.
  • XML-escaping for prompt injection safety.
  • Resource reads are guarded against path traversal and symlink escape.
  • Only skills from trusted sources should be used.

Out of Scope

  • Scripts execution, which will be added in one of the following PRs.

Closes: #3499

Copilot AI review requested due to automatic review settings February 20, 2026 11:04
@markwallace-microsoft Mark Wallace (markwallace-microsoft) added documentation Usage: [Issues, PRs], Target: documentation in the code base and learn docs .NET Usage: [Issues, PRs], Target: .Net labels Feb 20, 2026
@github-actions github-actions Bot changed the title Add FileAgentSkillsProvider for filesystem-based Agent Skills .NET: Add FileAgentSkillsProvider for filesystem-based Agent Skills Feb 20, 2026
@SergeyMenshykh SergeyMenshykh changed the title .NET: Add FileAgentSkillsProvider for filesystem-based Agent Skills .NET: Support Agent Skills Feb 20, 2026
@SergeyMenshykh
Fix file encoding: add UTF-8 BOM to .cs files
ee96900 
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot AI reviewed Feb 20, 2026
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Pull request overview

Adds a new .NET AIContextProvider that discovers Agent Skills from the filesystem and exposes them to agents via progressive disclosure (advertise → load → read resources), along with tests and a getting-started sample.

Changes:

  • Introduces FileAgentSkillsProvider + supporting loader/types to discover SKILL.md skills, advertise them via injected instructions, and expose load_skill / read_skill_resource tools.
  • Adds unit tests for discovery/parsing/resource-reading and updates projects to suppress the experimental diagnostic (MAAI001).
  • Adds a new Getting Started “Agent Skills” sample and wires it into the samples index/solution.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 9 comments.

Show a summary per file
File Description
dotnet/tests/Microsoft.Agents.AI.UnitTests/Microsoft.Agents.AI.UnitTests.csproj Suppresses experimental diagnostic in unit tests.
dotnet/tests/Microsoft.Agents.AI.UnitTests/AgentSkills/FileAgentSkillsProviderTests.cs Tests provider prompt/tool injection behavior and customization.
dotnet/tests/Microsoft.Agents.AI.UnitTests/AgentSkills/FileAgentSkillLoaderTests.cs Tests skill discovery/parsing/resource validation and read behavior.
dotnet/src/Microsoft.Agents.AI/Skills/SkillFrontmatter.cs Adds parsed frontmatter type for skill metadata.
dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillsProviderOptions.cs Adds options for customizing the advertisement prompt template.
dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillsProvider.cs Implements the context provider and exposes the two skill tools.
dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillLoader.cs Implements discovery, frontmatter parsing, and resource validation/reading.
dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkill.cs Adds internal representation of a loaded skill (body + resources).
dotnet/src/Microsoft.Agents.AI/Microsoft.Agents.AI.csproj Enables diagnostic IDs/experimental attribute injection and suppresses MAAI001.
dotnet/samples/GettingStarted/README.md Links new Agent Skills section from Getting Started index.
dotnet/samples/GettingStarted/AgentSkills/README.md Adds index README for Agent Skills samples.
dotnet/samples/GettingStarted/AgentSkills/Agent_Step01_BasicSkills/skills/expense-report/references/POLICY_FAQ.md Adds sample skill reference document.
dotnet/samples/GettingStarted/AgentSkills/Agent_Step01_BasicSkills/skills/expense-report/assets/expense-report-template.md Adds sample skill asset template.
dotnet/samples/GettingStarted/AgentSkills/Agent_Step01_BasicSkills/skills/expense-report/SKILL.md Adds sample skill with frontmatter + resource links.
dotnet/samples/GettingStarted/AgentSkills/Agent_Step01_BasicSkills/README.md Documents the sample and how progressive disclosure works.
dotnet/samples/GettingStarted/AgentSkills/Agent_Step01_BasicSkills/Program.cs Demonstrates usage of FileAgentSkillsProvider with an agent.
dotnet/samples/GettingStarted/AgentSkills/Agent_Step01_BasicSkills/Agent_Step01_BasicSkills.csproj Adds sample project and copies skill content to output.
dotnet/agent-framework-dotnet.slnx Adds the new sample to the solution structure.

Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillsProvider.cs Resolved
Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillLoader.cs Resolved
Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkill.cs Resolved
Comment thread dotnet/tests/Microsoft.Agents.AI.UnitTests/AgentSkills/FileAgentSkillLoaderTests.cs Resolved
Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillsProvider.cs Resolved
Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillLoader.cs Resolved
Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillLoader.cs Resolved
Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillLoader.cs Resolved
Comment thread dotnet/src/Microsoft.Agents.AI/Skills/FileAgentSkillsProvider.cs Resolved
@SergeyMenshykh
Fix final newline and simplify new expressions
bc23952 
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@SergeyMenshykh
Fix broken links in Agent Skills sample README
6b33e22 
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@SergeyMenshykh
Add null check for skillPaths parameter
2db5638 
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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integration — ad73840b Deployed Feb 20, 2026 by SergeyMenshykh via dotnet-build-and-test (net10.0, ubuntu-latest, Release, true, integration) #12631
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@rogerbarreto Roger Barreto (rogerbarreto) rogerbarreto approved these changes
@westey-m westey (westey-m) westey-m approved these changes
+1 more reviewer
@lokitoth Jacob Alber (lokitoth) lokitoth approved these changes
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@SergeyMenshykh SergeyMenshykh

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documentation Usage: [Issues, PRs], Target: documentation in the code base and learn docs .NET Usage: [Issues, PRs], Target: .Net

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Agent Framework
Status: Done

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Support for Agent Skills

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@SergeyMenshykh @lokitoth @rogerbarreto @westey-m @markwallace-microsoft