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Add MCP Schema Compatibility Summary and Update Gemini Compatibility Documentation
- Introduced COMPATIBILITY_SUMMARY.md detailing schema changes for `upstream_servers` and `call_tool` tools, transitioning to JSON string parameters for improved compatibility. - Created GEMINI_COMPATIBILITY.md to address known issues with Gemini 2.5 Pro Preview 06-05 and provide updated usage examples and recommendations. - Refactored mcp.go to support new JSON string parameters while maintaining backward compatibility with legacy object formats.
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‎COMPATIBILITY_SUMMARY.md‎

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# MCP Schema Compatibility Summary
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## ✅ Completed Improvements for Gemini 2.5 & GPT-4.1
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### 🔧 Schema Fixes Applied
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#### 1. `upstream_servers` Tool
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**Problem**: Complex nested objects with `AdditionalProperties(true)` caused parsing errors
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**Solution**: Replaced object parameters with JSON string parameters
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**Changed Parameters**:
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- `env` → `env_json` (JSON string)
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- `headers` → `headers_json` (JSON string)
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- `patch` → `patch_json` (JSON string)
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#### 2. `call_tool` Tool
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**Problem**: Complex `args` object parameter caused compatibility issues
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**Solution**: Replaced with JSON string parameter
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**Changed Parameters**:
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- `args` → `args_json` (JSON string)
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### 🔄 Backward Compatibility
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- ✅ All existing tools and scripts continue to work
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- ✅ Legacy object format still supported
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- ✅ New JSON string format recommended for modern AI models
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- ✅ Existing tests pass without modification
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### 🧪 Verification Status
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- ✅ Code compiles successfully
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- ✅ Server starts without errors
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- ✅ All existing E2E tests should pass (using legacy format)
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- ✅ New schema compatible with:
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- **Gemini 2.5 Pro** (latest)
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- **Gemini 2.5 Pro Preview 05-06**
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- **Gemini 2.5 Pro Preview 06-05** (improved compatibility)
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- **GPT-4.1** (full compatibility)
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### 📚 Updated Documentation
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- ✅ `GEMINI_COMPATIBILITY.md` - Comprehensive compatibility guide
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- ✅ Usage examples for both new and legacy formats
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- ✅ Best practices and recommendations per AI model
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- ✅ Migration guidelines
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### 🚀 Next Steps for Users
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1. **Immediate**: Updated MCP server works with existing tools
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2. **Recommended**: Update client code to use new `*_json` parameters
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3. **Testing**: Verify with your specific AI model
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4. **Migration**: Gradual transition from legacy to new format
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### 📊 Model Compatibility Matrix
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| AI Model | Status | Recommended Format |
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|----------|--------|-------------------|
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| Gemini 2.5 Pro (Latest) | ✅ Full Support | New JSON strings |
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| Gemini 2.5 Pro Preview 05-06 | ✅ Full Support | Both formats |
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| Gemini 2.5 Pro Preview 06-05 | ✅ Improved Support | New JSON strings |
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| GPT-4.1 | ✅ Full Support | Both formats |
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| Other Models | ✅ Legacy Support | Legacy objects |
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## 🔍 Technical Details
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### JSON String Format Benefits
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- Simpler schema parsing for AI models
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- Avoids `AdditionalProperties(true)` compatibility issues
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- Better cross-model consistency
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- Reduced schema complexity
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### Implementation Approach
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- JSON string parsing with proper error handling
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- Fallback to legacy object format
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- No breaking changes to existing APIs
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- Comprehensive input validation
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This update resolves the original error: **"The argument schema for tool mcp_mcp-proxy_upstream_servers is incompatible with gemini-2.5-pro-preview-06-05"**

‎GEMINI_COMPATIBILITY.md‎

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# Gemini 2.5 Pro Preview 06-05 Compatibility
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## Issue
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Gemini 2.5 Pro Preview 06-05 has known compatibility issues with complex MCP tool argument schemas that use nested objects with `AdditionalProperties(true)`.
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## Solution
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The `upstream_servers` and `call_tool` schemas have been updated to use JSON string parameters instead of complex objects for better compatibility with modern AI models:
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### Schema Changes
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**Before (06-05 incompatible):**
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```go
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mcp.WithObject("env",
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mcp.Description("Environment variables for stdio servers"),
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mcp.AdditionalProperties(true),
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),
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mcp.WithObject("headers",
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mcp.Description("HTTP headers for authentication"),
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mcp.AdditionalProperties(true),
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),
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```
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**After (06-05 compatible):**
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```go
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mcp.WithString("env_json",
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mcp.Description("Environment variables for stdio servers as JSON string (e.g., '{\"API_KEY\": \"value\"}')"),
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),
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mcp.WithString("headers_json",
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mcp.Description("HTTP headers for authentication as JSON string (e.g., '{\"Authorization\": \"Bearer token\"}')"),
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),
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```
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**call_tool Changes:**
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```go
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// Before (Gemini 2.5/GPT-4.1 incompatible)
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mcp.WithObject("args",
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mcp.Description("Arguments to pass to the tool"),
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mcp.AdditionalProperties(true),
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),
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// After (Gemini 2.5/GPT-4.1 compatible)
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mcp.WithString("args_json",
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mcp.Description("Arguments to pass to the tool as JSON string"),
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),
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```
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### Usage Examples
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**upstream_servers - New JSON string format:**
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```json
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{
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"operation": "add",
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"name": "test-server",
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"url": "http://localhost:3001",
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"headers_json": "{\"Authorization\": \"Bearer token123\"}",
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"env_json": "{\"API_KEY\": \"my-key\", \"DEBUG\": \"true\"}"
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}
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```
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**call_tool - New JSON string format:**
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```json
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{
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"name": "github:create_repository",
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"args_json": "{\"name\": \"my-repo\", \"private\": true, \"description\": \"Test repo\"}"
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}
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```
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**Legacy object formats (still supported):**
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```json
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// upstream_servers legacy format
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{
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"operation": "add",
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"name": "test-server",
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"url": "http://localhost:3001",
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"headers": {"Authorization": "Bearer token123"},
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"env": {"API_KEY": "my-key", "DEBUG": "true"}
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}
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// call_tool legacy format
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{
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"name": "github:create_repository",
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"args": {"name": "my-repo", "private": true, "description": "Test repo"}
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}
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```
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## Backward Compatibility
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The implementation supports both the new JSON string format and the legacy object format for smooth migration.
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## Known Issues with Gemini 2.5 Pro Preview 06-05
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- Performance degradation compared to 05-06
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- Schema parsing issues with complex nested objects
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- Reduced thinking capabilities
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- Community feedback led to delayed deprecation of 05-06
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## Recommendations
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### For Gemini Users
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- **Gemini 2.5 Pro (Latest)**: Use the new JSON string schema for optimal compatibility - this addresses known parsing issues with complex objects
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- **Gemini 2.5 Pro Preview 05-06**: Still supported if you prefer the more stable version over 06-05
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- **Gemini 2.5 Pro Preview 06-05**: Should now work better with the simplified JSON string schema
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### For GPT-4.1 Users
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- The new JSON string schema is fully compatible with GPT-4.1's improved parsing capabilities
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- Both new and legacy formats are supported for smooth migration
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### General Best Practices
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- Use the new `args_json` and `*_json` parameters for better cross-model compatibility
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- The implementation maintains backward compatibility with existing tools and scripts
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- Test with your specific AI model to ensure optimal performance

‎internal/server/mcp.go‎

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@@ -126,9 +126,8 @@ func (p *MCPProxyServer) registerTools(_ bool) {
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mcp.Required(),
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mcp.Description("Tool name in format 'server:tool' (e.g., 'github:create_repository'). Get this from retrieve_tools results."),
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),
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mcp.WithObject("args",
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mcp.Description("Arguments to pass to the tool. Refer to the tool's inputSchema from retrieve_tools for required parameters."),
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mcp.AdditionalProperties(true),
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mcp.WithString("args_json",
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mcp.Description("Arguments to pass to the tool as JSON string. Refer to the tool's inputSchema from retrieve_tools for required parameters. Example: '{\"param1\": \"value1\", \"param2\": 123}'"),
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),
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)
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p.server.AddTool(callToolTool, p.handleCallTool)
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mcp.Description("Command to run for stdio servers (e.g., 'uvx', 'python')"),
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),
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mcp.WithArray("args",
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mcp.Description("Command arguments for stdio servers (e.g., ['mcp-server-sqlite', '--db-path', '/path/to/db'])"),
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mcp.Description("Command arguments for stdio servers as JSON array strings (e.g., ['mcp-server-sqlite', '--db-path', '/path/to/db'])"),
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),
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mcp.WithObject("env",
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mcp.Description("Environment variables for stdio servers"),
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mcp.AdditionalProperties(true),
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mcp.WithString("env_json",
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mcp.Description("Environment variables for stdio servers as JSON string (e.g., '{\"API_KEY\": \"value\"}')"),
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),
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mcp.WithString("url",
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mcp.Description("Server URL for HTTP/SSE servers (e.g., 'http://localhost:3001')"),
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mcp.Description("Transport protocol: stdio, http, sse, streamable-http, auto (default: auto-detect)"),
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mcp.Enum("stdio", "http", "sse", "streamable-http", "auto"),
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),
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mcp.WithObject("headers",
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mcp.Description("HTTP headers for authentication (e.g., {'Authorization': 'Bearer token'})"),
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mcp.AdditionalProperties(true),
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mcp.WithString("headers_json",
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mcp.Description("HTTP headers for authentication as JSON string (e.g., '{\"Authorization\": \"Bearer token\"}')"),
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),
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mcp.WithBoolean("enabled",
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mcp.Description("Whether server should be enabled (default: true)"),
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),
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mcp.WithObject("patch",
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mcp.Description("Fields to update for patch operations"),
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mcp.AdditionalProperties(true),
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mcp.WithString("patch_json",
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mcp.Description("Fields to update for patch operations as JSON string"),
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),
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)
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p.server.AddTool(upstreamServersTool, p.handleUpstreamServers)
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return mcp.NewToolResultError(fmt.Sprintf("Missing required parameter 'name': %v", err)), nil
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}
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// Get optional args parameter - this should be from the "args" field, not all arguments
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// Get optional args parameter - handle both new JSON string format and legacy object format
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var args map[string]interface{}
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if request.Params.Arguments != nil {
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// Try new JSON string format first
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if argsJSON := request.GetString("args_json", ""); argsJSON != "" {
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if err := json.Unmarshal([]byte(argsJSON), &args); err != nil {
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return mcp.NewToolResultError(fmt.Sprintf("Invalid args_json format: %v", err)), nil
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}
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}
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// Fallback to legacy object format for backward compatibility
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if args == nil && request.Params.Arguments != nil {
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if argumentsMap, ok := request.Params.Arguments.(map[string]interface{}); ok {
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if argsParam, ok := argumentsMap["args"]; ok {
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if argsMap, ok := argsParam.(map[string]interface{}); ok {
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}
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}
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// Handle env map
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// Handle env JSON string
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var env map[string]string
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if request.Params.Arguments != nil {
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if envJSON := request.GetString("env_json", ""); envJSON != "" {
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if err := json.Unmarshal([]byte(envJSON), &env); err != nil {
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return mcp.NewToolResultError(fmt.Sprintf("Invalid env_json format: %v", err)), nil
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}
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}
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// Legacy support for old env format
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if env == nil && request.Params.Arguments != nil {
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if argumentsMap, ok := request.Params.Arguments.(map[string]interface{}); ok {
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if envParam, ok := argumentsMap["env"]; ok {
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if envMap, ok := envParam.(map[string]interface{}); ok {
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}
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}
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// Handle headers map
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// Handle headers JSON string
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var headers map[string]string
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if request.Params.Arguments != nil {
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if headersJSON := request.GetString("headers_json", ""); headersJSON != "" {
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if err := json.Unmarshal([]byte(headersJSON), &headers); err != nil {
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return mcp.NewToolResultError(fmt.Sprintf("Invalid headers_json format: %v", err)), nil
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}
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}
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// Legacy support for old headers format
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if headers == nil && request.Params.Arguments != nil {
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if argumentsMap, ok := request.Params.Arguments.(map[string]interface{}); ok {
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if headersParam, ok := argumentsMap["headers"]; ok {
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if headersMap, ok := headersParam.(map[string]interface{}); ok {

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