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JSON MCP Server

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A high-performance MCP server for comprehensive JSON file operations, including reading, writing, and advanced querying, optimized for LLM interactions.

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JSON MCP Server

A high-performance Rust-based Model Context Protocol (MCP) server that provides comprehensive JSON file operations optimized for LLM interactions. This server enables LLMs to efficiently read, write, query, and manipulate JSON files with support for extremely large datasets and advanced querying capabilities.

🚀 Features

Core JSON Tools

  • 📖 json-read: Read JSON files with optional JSONPath filtering and pagination
  • ✏️ json-write: Write or update JSON files with multiple merge strategies
  • 🔍 json-query: Execute complex JSONPath queries with various output formats
  • ✅ json-validate: Validate JSON structure and syntax with detailed diagnostics
  • ❓ json-help: Interactive help system with comprehensive examples and troubleshooting

Key Capabilities

  • Large File Support: Efficient pagination and streaming for files of any size
  • JSONPath Querying: Full JSONPath support for complex data extraction and filtering
  • Flexible Writing: Multiple modes (replace, merge_shallow, merge_deep, append) with backup options
  • LLM-Optimized: Detailed error messages and usage examples for optimal LLM interaction
  • Memory Efficient: Smart pagination prevents memory overflow on large datasets
  • MCP Compliant: Full Model Context Protocol support with proper error handling
  • Debug Logging: File-based debug logging for troubleshooting without violating MCP protocol

Tool Reference

json-read

Read and parse JSON files with optional JSONPath filtering and pagination.

Parameters:

  • file_path (string, required): Path to JSON file
  • json_path (string, optional): JSONPath expression for filtering
  • start_index (integer, optional): Starting index for pagination (default: 0)
  • limit (integer, optional): Maximum items to return (default: 1000)
  • output_format (string, optional): Output format - "json", "pretty", "compact" (default: "json")

json-write

Write or update JSON files with flexible merge strategies.

Parameters:

  • file_path (string, required): Path to JSON file
  • content (string, required): JSON content to write
  • mode (string, optional): Write mode - "replace", "merge_shallow", "merge_deep", "append" (default: "replace")

json-query

Execute JSONPath queries on JSON files with various output formats.

Parameters:

  • file_path (string, required): Path to JSON file
  • json_path (string, required): JSONPath query expression
  • output_format (string, optional): Output format - "json", "pretty", "compact", "csv", "markdown" (default: "json")

json-validate

Validate JSON file structure and syntax.

Parameters:

  • file_path (string, required): Path to JSON file to validate

json-help

Get comprehensive help about available tools and JSONPath syntax.

Parameters:

  • topic (string, optional): Help topic - "overview", "tools", "jsonpath", "examples", "troubleshooting" (default: "overview")

JSONPath Support

The server supports full JSONPath syntax for querying JSON data:

  • $ - Root element
  • .field - Child field access
  • [index] - Array index access
  • [*] - All array elements
  • ..field - Recursive descent
  • [?(@.field > value)] - Filter expressions
  • {field1, field2} - Projection

JSONPath Examples

Copy & paste — that's it
# Get all user names
$.users[*].name

# Filter users over 25
$.users[?(@.age > 25)]

# Get nested data
$.data.items[*].details.price

# All prices anywhere in document  
$..price

# Complex filtering
$.products[?(@.category == 'electronics' && @.price < 500)].name

Performance Notes

Large File Handling

  • Files of any size: The json-read tool automatically uses streaming for memory efficiency
  • Line-delimited JSON: Automatically detected and processed efficiently
  • Memory usage: Streaming keeps memory usage constant regardless of file size

Best Practices

  • Use specific JSONPath queries to filter data early
  • Set reasonable limits when processing large datasets
  • Use offset for pagination through large result sets
  • The server automatically optimizes for file size and available memory

Error Handling

The server provides detailed error messages to help diagnose issues:

  • File not found: Clear path resolution guidance
  • JSON syntax errors: Line and column information when available
  • JSONPath errors: Syntax validation and suggestions
  • Memory issues: Guidance on using streaming alternatives

Development

Project Structure

Copy & paste — that's it
json-mcp-server/
├── src/                    # Source code
│   ├── main.rs            # Application entry point and MCP server
│   ├── lib.rs             # Library exports for testing
│   ├── mcp/               # MCP protocol implementation
│   │   ├── mod.rs
│   │   ├── protocol.rs    # Protocol definitions and types
│   │   └── server.rs      # MCP server implementation
│   └── json_tools/        # JSON tool implementations
│       ├── mod.rs
│       ├── handler.rs     # Tool coordination and help system
│       ├── operations.rs  # Read/write/validate operations
│       ├── query.rs       # JSONPath querying with multiple formats
│       └── streaming.rs   # Large file streaming and pagination
├── tests/                 # Integration tests
│   └── integration_tests.rs
├── examples/              # Example configurations and data
│   ├── mcp_clients/       # Client configuration guides
│   │   ├── vscode.md      # VS Code setup
│   │   ├── claude-desktop.md
│   │   ├── github-copilot.md
│   │   ├── generic.md     # Generic MCP client setup
│   │   ├── client_implementation.md
│   │   └── python_client.py
│   ├── sample-data.json   # Sample test data
│   ├── test-commands.jsonl
│   └── test-output.json
├── dev_tools/             # Development and testing utilities
│   ├── README.md          # Development tools documentation
│   └── testing/           # Test scripts and utilities
│       ├── test_all_tools.py
│       ├── test_multiple_instances.py
│       ├── test_json_help.py
│       └── [other test files]
├── Cargo.toml            # Rust project configuration
└── README.md             # This file

Building

Copy & paste — that's it
# Development build
cargo build

# Release build  
cargo build --release

# Run tests
cargo test

# Check for issues
cargo check

Dependencies

  • tokio: Async runtime
  • serde/serde_json: JSON serialization
  • jsonpath-rust: JSONPath query support
  • anyhow: Error handling
  • clap: Command line parsing

License

This project is licensed under the MIT OR Apache-2.0 license.

Contributing

Contributions are welcome! Please ensure:

  1. Code follows Rust conventions
  2. All tests pass
  3. New features include appropriate tests
  4. Documentation is updated for new functionality

Support

For issues, questions, or contributions, please refer to the project repository.