Add MCP_DISABLE_EMBEDDED_RESOURCES feature flag for client compatibility by Copilot · Pull Request #1956 · github/github-mcp-server

Copilot · 2026-02-04T12:24:14Z

Summary

Adds MCP_DISABLE_EMBEDDED_RESOURCES feature flag to return file contents as standard MCP content types (TextContent/ImageContent) instead of EmbeddedResource, improving compatibility with clients like Antigravity.

Why

Some MCP clients have limited embedded resource support, causing get_file_contents to fail or display incorrectly.

What changed

Added FeatureFlagDisableEmbeddedResources constant to pkg/github/feature_flags.go
Updated NewToolResultResource() in pkg/utils/result.go to accept flag parameter:
- Text files → TextContent with MIME type in metadata
- Binary files → ImageContent with raw binary data
- Default → EmbeddedResource (backward compatible)
Updated get_file_contents to check flag once and pass to utility function (simplified from duplicate checks)
Added Feature Flags section to docs/server-configuration.md with simplified configuration guidance
Added troubleshooting note to Antigravity installation guide

MCP impact

Tool schema or behavior changed

get_file_contents behavior changes when feature flag is enabled. Schema unchanged. Default behavior (flag disabled) preserves existing EmbeddedResource format.

Prompts tested (tool changes only)

"Get the contents of README.md in github/github-mcp-server" (text file)
"Show me the logo.png file from the repo" (binary file)
Verified both with flag enabled and disabled

Security / limits

No security or limits impact

Feature flag only changes content serialization format. No auth, data exposure, or rate limit implications.

Tool renaming

I am not renaming tools as part of this PR

Lint & tests

Linted locally with ./script/lint
Tested locally with ./script/test

Docs

Updated (README / docs / examples)

Added Feature Flags section to server configuration guide and troubleshooting note to Antigravity installation guide. Documentation simplified to remove remote server references and focus on local server configuration.

Original prompt

Using the feature flag checker in the passed in deps to tool calls, instead of returning an embedded resource always in the get_file_contents tool, let's add a flag MCP_DISABLE_EMBEDDED_RESOURCES, and when that flag is on, we do our best to return the text or base64 encoded binary content with mime type etc. the same as we would, but as general MCP content and not as embedded resource?

We should then update the docs for any clients mentioned in issues in this repository as failing to get file content (just missing), and same with spaces tool, but that's only in remote server repository, so you can't fix that (but it'll use the same feature flag).

It should be simple if conditions for the flag, at the leaf nodes where we set the return content. Make it simple, clear etc.

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

- Added FeatureFlagDisableEmbeddedResources constant to feature_flags.go - Implemented NewToolResultResourceWithFlag in utils/result.go - When flag is enabled, returns TextContent for text files - Returns ImageContent with base64 data for binary files - Maintains backward compatibility when flag is disabled - Updated get_file_contents tool to check feature flag and use new function - Added comprehensive tests for both utils function and integration with get_file_contents Co-authored-by: SamMorrowDrums <4811358+SamMorrowDrums@users.noreply.github.com>

- Added Feature Flags section to server-configuration.md - Added troubleshooting note to Antigravity installation guide - Fixed linter issue in result_test.go - Generated updated documentation Co-authored-by: SamMorrowDrums <4811358+SamMorrowDrums@users.noreply.github.com>

The MCP SDK handles base64 encoding during JSON marshaling, so the Data field should contain raw binary data, not pre-encoded base64 strings. This prevents double-encoding where base64 strings were being encoded again. - Updated NewToolResultResourceWithFlag to pass raw binary data - Updated test to verify raw binary data instead of base64 string - Removed unused encoding/base64 imports Co-authored-by: SamMorrowDrums <4811358+SamMorrowDrums@users.noreply.github.com>

- Updated test to verify raw binary data matches expected value - Fixed comment to accurately describe what is being verified - Ensures test properly validates SDK's base64 encoding behavior Co-authored-by: SamMorrowDrums <4811358+SamMorrowDrums@users.noreply.github.com>

Copilot

Pull request overview

This PR adds the MCP_DISABLE_EMBEDDED_RESOURCES feature flag to improve compatibility with MCP clients that have limited embedded resource support. When enabled, the get_file_contents tool returns file contents as standard MCP content types (TextContent for text files, ImageContent for binary files) instead of EmbeddedResource.

Changes:

Added runtime feature flag MCP_DISABLE_EMBEDDED_RESOURCES to control content serialization format
Created NewToolResultResourceWithFlag() utility function with conditional logic based on flag state
Updated get_file_contents tool to check flag and use new utility function at all return sites
Added comprehensive test coverage for flag-enabled and flag-disabled scenarios
Documented feature flag usage and added troubleshooting guidance for Antigravity client

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/github/feature_flags.go	Defines the new `MCP_DISABLE_EMBEDDED_RESOURCES` feature flag constant with documentation
pkg/utils/result.go	Implements `NewToolResultResourceWithFlag()` to return TextContent/ImageContent when flag is enabled, with fallback to EmbeddedResource
pkg/utils/result_test.go	Comprehensive unit tests covering all branches: flag disabled, text content with flag, binary content with flag, and empty content fallback
pkg/github/repositories.go	Updates `get_file_contents` to check feature flag at 4 return sites (text/binary with/without SHA)
pkg/github/repositories_test.go	Integration tests verifying flag behavior with mocked HTTP client for text and binary files
docs/server-configuration.md	Adds Feature Flags section documenting flag purpose, usage, and configuration for local/remote servers
docs/installation-guides/install-antigravity.md	Adds troubleshooting guidance for file content display issues with note about upcoming remote server support

Copilot · 2026-02-04T13:04:55Z

pkg/utils/result.go

+			},
+		}
+	case len(contents.Blob) > 0:
+		// Binary content - use ImageContent with base64 data


This comment mentions "base64 data" which could be misleading. ImageContent stores raw binary data in the Data field, not base64-encoded data. The SDK handles the base64 encoding only during JSON marshaling (as noted in the comment below), so this comment should say "Binary content - use ImageContent with raw binary data" to be more accurate.

Suggested change

// Binary content - use ImageContent with base64 data

// Binary content - use ImageContent with raw binary data

Fixed in 916c71b - updated comment to say "Binary content - use ImageContent with raw binary data".

Copilot · 2026-02-04T13:04:55Z

pkg/utils/result.go

+	var content mcp.Content
+	switch {
+	case contents.Text != "":
+		// Text content - use TextContent with mime type in annotations


The comment incorrectly states "mime type in annotations" but the MIME type is actually stored in Meta, not Annotations. The comment should be corrected to say "mime type in metadata" or "mime type in Meta" for accuracy.

Suggested change

// Text content - use TextContent with mime type in annotations

// Text content - use TextContent with mime type in metadata (Meta)

Fixed in 916c71b - updated comment to say "Text content - use TextContent with MIME type in metadata".

SamMorrowDrums

@copilot I left a bunch of cleanup suggestions amounting to:

no trailers in documentation
ignore remote server, just document the ENV and arg methods for STDIO server feature flag configuration
no pointless function rename

SamMorrowDrums · 2026-02-04T13:03:13Z

docs/installation-guides/install-antigravity.md

+
+If you experience issues with the `get_file_contents` tool not displaying file contents correctly, this may be due to limited embedded resource support in some versions of Antigravity.
+
+**Solution:** The remote GitHub MCP Server will soon support the `MCP_DISABLE_EMBEDDED_RESOURCES` feature flag to improve compatibility. This flag makes file contents return as standard MCP content types that work better across different clients.


@copilot the spoiler soon support is not good. Neither is for updates on this feature you should just document. We can ignore the remote server entirely for now, and update that once it's shipped.

Updated in 916c71b - removed "soon support" and "for updates" references, simplified to just document the known limitation.

SamMorrowDrums · 2026-02-04T13:04:42Z

docs/server-configuration.md

+**Coming soon:** Remote server support for this flag will be available in the next release.
+
+</td>
+<td>
+
+Feature flags are checked at runtime via the feature flag checker. Configuration method depends on your deployment:
+
+**For custom integrations:**
+```go
+featureChecker := func(ctx context.Context, flagName string) (bool, error) {
+    if flagName == "MCP_DISABLE_EMBEDDED_RESOURCES" {
+        return true, nil // Enable the flag
+    }
+    return false, nil
+}
+```
+
+</td>
+</tr>
+</table>
+
+> **Note:** This feature flag does not affect other tools, only `get_file_contents`. The default behavior (embedded resources) is maintained when the flag is not enabled, ensuring backward compatibility.


All of the selection is redundant. We don't need to add trailers or describe what tools it does or doesn't do or mention the remote server yet.

Removed in 916c71b - simplified to just explain what the flag does and that it's configured via feature flag checker, removed remote server references and extra notes.

SamMorrowDrums · 2026-02-04T13:05:53Z

pkg/github/repositories.go

 						// Include SHA in the result metadata
 						if fileSHA != "" {
-							return utils.NewToolResultResource(fmt.Sprintf("successfully downloaded text file (SHA: %s)", fileSHA)+successNote, result), nil, nil
+							return utils.NewToolResultResourceWithFlag(fmt.Sprintf("successfully downloaded text file (SHA: %s)", fileSHA)+successNote, result, disableEmbedded), nil, nil


Did we need to rename this function at all? I don't think so, the flag is not material to the naming of the function, it's just a new argument. @copilot

Fixed in 916c71b - reverted to using NewToolResultResource with the flag as a new parameter instead of creating a separate function.

SamMorrowDrums · 2026-02-04T13:06:10Z

pkg/github/repositories.go

 						MIMEType: contentType,
 					}
+					// Check if embedded resources should be disabled
+					disableEmbedded := deps.IsFeatureEnabled(ctx, FeatureFlagDisableEmbeddedResources)


Are we checking this twice in same function?

Fixed in 916c71b - moved flag check before the if/else block so it's only checked once and reused for both text and binary content paths.

- Reverted function rename: NewToolResultResource now takes flag parameter directly - Fixed duplicate flag checks: check once and reuse variable - Fixed comments: "base64 data" → "raw binary data", "annotations" → "metadata" - Simplified Antigravity docs: removed "soon support" and update references - Simplified server-configuration.md: removed remote server mentions and redundant notes Co-authored-by: SamMorrowDrums <4811358+SamMorrowDrums@users.noreply.github.com>

Copilot · 2026-02-04T13:12:02Z

@copilot I left a bunch of cleanup suggestions amounting to:

no trailers in documentation...

All addressed in 916c71b:

Removed trailers and "soon support" from documentation
Removed remote server references, documented feature flag configuration only
Reverted function rename - NewToolResultResource now takes flag as parameter

Initial plan

183705f

Copilot AI assigned Copilot and SamMorrowDrums Feb 4, 2026

Copilot started work on behalf of SamMorrowDrums February 4, 2026 12:24 View session

Copilot AI and others added 4 commits February 4, 2026 12:32

Copilot AI changed the title ~~[WIP] Add flag to disable embedded resources in get_file_contents tool~~ Add MCP_DISABLE_EMBEDDED_RESOURCES feature flag for client compatibility Feb 4, 2026

Copilot AI requested a review from SamMorrowDrums February 4, 2026 12:41

Copilot finished work on behalf of SamMorrowDrums February 4, 2026 12:41

SamMorrowDrums marked this pull request as ready for review February 4, 2026 13:01

SamMorrowDrums requested a review from a team as a code owner February 4, 2026 13:01

Copilot AI review requested due to automatic review settings February 4, 2026 13:01

Copilot started reviewing on behalf of SamMorrowDrums February 4, 2026 13:01 View session

Copilot AI reviewed Feb 4, 2026

View reviewed changes

SamMorrowDrums reviewed Feb 4, 2026

View reviewed changes

Copilot started work on behalf of SamMorrowDrums February 4, 2026 13:08 View session

Copilot AI requested a review from SamMorrowDrums February 4, 2026 13:13

Copilot finished work on behalf of SamMorrowDrums February 4, 2026 13:13

	// Binary content - use ImageContent with base64 data
	// Binary content - use ImageContent with raw binary data

	// Text content - use TextContent with mime type in annotations
	// Text content - use TextContent with mime type in metadata (Meta)


		If you experience issues with the `get_file_contents` tool not displaying file contents correctly, this may be due to limited embedded resource support in some versions of Antigravity.

		Solution: The remote GitHub MCP Server will soon support the `MCP_DISABLE_EMBEDDED_RESOURCES` feature flag to improve compatibility. This flag makes file contents return as standard MCP content types that work better across different clients.

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Summary

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