MCP JSON Tools

@zfirsty

About MCP JSON Tools

MCP server providing tools to query, inspect, and modify local JSON files.

Config

Add this server to your MCP-compatible client using the configuration below.

{
  "mcpServers": {
    "jsonTools": {
      "description": "Tools to query, inspect, and modify local JSON and NDJSON files.",
      "command": "npx",
      "args": [
        "mcp-json-tools"
      ]
    }
  }
}

Tools

Executes a JSONPath query on a local JSON or NDJSON file and returns an array of matching values. Reads both formats automatically; NDJSON is treated as an array of objects for querying. **Syntax Note**: Use `$.path...` for JSON objects and `$[selector]` (e.g., `$[*]` or `$[?(...)]`) for NDJSON arrays.

Executes a JSONPath query on a local JSON or NDJSON file and returns matching nodes (value + path). Reads both formats automatically; NDJSON is treated as an array of objects for querying. **Syntax Note**: Use `$.path...` for JSON objects and `$[selector]` (e.g., `$[*]` or `$[?(...)]`) for NDJSON arrays.

Reads a JSON or NDJSON file, executes JavaScript code within a sandboxed VM with file content ($1, object for JSON, array for NDJSON), lodash (_), and jsonpath (jp). Returns the result OR modifies the file (preserving original format: JSON or NDJSON) if the code's last expression is { type: 'updateFile', data: <new_data> }. **Do not use explicit `return` for the final result/update object; the last evaluated expression is used.** Has a 30s timeout. **WARNING: Executes user-provided code.**

Reads multiple JSON or NDJSON files, executes JS code within a sandboxed VM with file contents ($1 is array of parsed contents), lodash (_), and jsonpath (jp). Returns the result OR modifies files (preserving original formats) if the code's last expression is { type: 'updateMultipleFiles', updates: [...] }. **Do not use explicit `return` for the final result/update object; the last evaluated expression is used.** Has a 30s timeout. **WARNING: Executes user-provided code.**

Overview

What is MCP JSON Tools?

MCP JSON Tools is an MCP server that lets you interact with local JSON and NDJSON (JSONL) files by querying with JSONPath and manipulating data via Lodash. It provides four tools—mcp_json_query, mcp_json_nodes, mcp_json_eval, and mcp_json_multi_eval—for developers using MCP‑compatible clients like Cursor or VS Code.

How to use MCP JSON Tools?

Configure your client to run the server via npx (recommended) or Node directly. In your client’s mcp.json (e.g., for Cursor or VS Code), set "command": "npx" and "args": ["mcp-json-tools"]. When using npx, all file paths passed to the tools must be absolute paths. Tools accept parameters such as file_path, json_path, js_code, and optionally count.

Key features of MCP JSON Tools

Unified format handling: reads both JSON and NDJSON automatically
Query data using standard JSONPath expressions (mcp_json_query)
Inspect values and their precise paths (mcp_json_nodes)
Analyze or modify files with sandboxed JavaScript (Lodash + JSONPath) (mcp_json_eval, mcp_json_multi_eval)
Modifications preserve the original file format (JSON or NDJSON)
Safe execution via Node.js vm module with configurable timeouts

Use cases of MCP JSON Tools

Querying specific fields from a JSON file using JSONPath
Inspecting the structure of a JSON or NDJSON file by retrieving values and paths
Performing complex analysis (e.g., calculating averages) with custom JavaScript
Modifying JSON/NDJSON files in place (e.g., adding properties or filtering records)
Batch processing multiple JSON/NDJSON files simultaneously

FAQ from MCP JSON Tools

What file formats are supported?

JSON and newline-delimited JSON (NDJSON/JSONL). NDJSON files are automatically treated as an array of objects.

How can I modify a file?

Use mcp_json_eval (single file) or mcp_json_multi_eval (multiple files). The last expression in your JavaScript code must be { type: 'updateFile', data: <new_data> } (or { type: 'updateMultipleFiles', updates: [...] }).

What JavaScript libraries are available in the eval tools?

Lodash (as _) and jsonpath (as jp) are pre‑loaded in the sandboxed VM. The file content is available as $1 (object for JSON, array for NDJSON).

What is the timeout for eval tools?

Both mcp_json_eval and mcp_json_multi_eval have a 30‑second timeout.

Is the sandboxed execution fully secure?

No. The code runs inside Node.js’s vm module, which is safer than raw eval() but still poses risks of resource exhaustion or unintended logic. Only execute trusted code.

Frequently asked questions

What file formats are supported?

JSON and newline-delimited JSON (NDJSON/JSONL). NDJSON files are automatically treated as an array of objects.

How can I modify a file?

Use `mcp_json_eval` (single file) or `mcp_json_multi_eval` (multiple files). The last expression in your JavaScript code must be `{ type: 'updateFile', data: <new_data> }` (or `{ type: 'updateMultipleFiles', updates: [...] }`).

What JavaScript libraries are available in the eval tools?

Lodash (as `_`) and jsonpath (as `jp`) are pre‑loaded in the sandboxed VM. The file content is available as `$1` (object for JSON, array for NDJSON).

What is the timeout for eval tools?

Both `mcp_json_eval` and `mcp_json_multi_eval` have a 30‑second timeout.

Is the sandboxed execution fully secure?

No. The code runs inside Node.js’s `vm` module, which is safer than raw `eval()` but still poses risks of resource exhaustion or unintended logic. Only execute trusted code.

Comments

Basic information

More Other MCP servers

IDA Pro MCP

mrexodia

AI-powered reverse engineering assistant that bridges IDA Pro with language models through MCP.

9.9K

DeepMark

DeepMark helps teachers deliver rapid, consistent marking with meaningful feedback for every student — in a fraction of the time. What once took a week, now takes one free period.

YOUB

Connect your AI assistant to your own YOUB endurance training account. Read recorded activities with full analysis, planned sessions, race goals, wellness (HRV, sleep, resting HR) and your athletic profile. Create or mov

Inbox Zero AI

elie222

The world's best AI personal assistant for email. Open source app to help you reach inbox zero fast.

11.6K

Glasswarp

See and control a real Windows PC you own — from any MCP client, locally or remotely. Observe (UIA + screenshots), click/type/drag/scroll, launch apps, owner Live View. BYOH: your machine, your key.