feat(core): add tools to list and read MCP resources

[ruomengz]

Summary

This PR introduces core tools for interacting with MCP resources, allowing the agent to list and read static or dynamic resources exposed by MCP servers.

Details

• Tool Implementation:
  • list_mcp_resources: Lists all available resources across all connected MCP servers, with optional filtering by server name.
  • read_mcp_resource: Reads the content of a specific MCP resource identified by its URI.
• Core Enhancements:
  • Updated McpClientManager with methods to aggregate resources from all active clients.
  • Registered new tools in the core tool registry.
  • Enabled these tools in "Plan Mode" to allow the agent to research available resources before execution.
• Documentation:
  • Created docs/tools/mcp-resources.md with usage instructions and examples.
  • Updated docs/reference/tools.md and docs/sidebar.json to include the new tools.
• Testing:
  • Added comprehensive unit tests for the new tools and manager methods.
  • Added integration tests verifying end-to-end resource listing and reading with a mock MCP server.

Related Issues

Closes #25335

How to Validate

1. Run unit tests: npm test -w @google/gemini-cli-core -- src/tools/list-mcp-resources.test.ts src/tools/read-mcp-resource.test.ts
2. Run integration tests: npm run test:e2e -- integration-tests/mcp-resources.test.ts
3. Manual validation: Connect an MCP server with resources (e.g., the everything server) and use:
   • "list mcp resources"
   • "read mcp resource demo://resource/static/document/architecture.md"

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the agent's capabilities by adding tools to interact with Model Context Protocol (MCP) resources. By allowing the agent to list and read these resources, it can better leverage external data sources during its planning and execution phases. The changes include necessary infrastructure updates to manage resource aggregation and ensure these tools are properly exposed and validated.

Highlights

• New MCP Resource Tools: Introduced list_mcp_resources and read_mcp_resource tools to enable discovery and retrieval of data from connected MCP servers.
• Core Integration: Updated McpClientManager to aggregate resources and registered the new tools in the core tool registry, enabling them in Plan Mode.
• Documentation and Testing: Added comprehensive documentation, unit tests, and integration tests to ensure reliable resource interaction.

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[github-actions]

Size Change: +9.84 kB (+0.03%)

Total Size: 34.1 MB

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[gemini-code-assist]

Code Review

This pull request introduces support for Model Context Protocol (MCP) resources by adding two new tools: list_mcp_resources and read_mcp_resource. These tools enable the agent to discover and retrieve data from contextual resources provided by connected MCP servers. The implementation includes new tool definitions, updates to the McpClientManager for resource discovery, and logic in the ToolRegistry to conditionally enable these tools only when resources are available. Additionally, the PR provides comprehensive documentation and both unit and integration tests to ensure the new functionality works as expected. I have no feedback to provide.

[github-actions]

✅ 59 tests passed successfully on gemini-3-flash-preview.

🧠 Model Steering Guidance

This PR modifies files that affect the model's behavior (prompts, tools, or instructions).

• ⚠️ Consider adding Evals: No behavioral evaluations (evals/*.eval.ts) were added or updated in this PR. Consider adding a test case to verify the new behavior and prevent regressions.
• 🚀 Maintainer Reminder: Please ensure that these changes do not regress results on benchmark evals before merging.

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This is an automated guidance message triggered by steering logic signatures.

[chrstnb]

Looks great!