McpToolServer

A Model Context Protocol (MCP) server built with C# and ASP.NET Core that exposes 52 developer utility tools to LLMs.

The server implements the MCP specification so any compatible host (Claude Desktop, VS Code Copilot, Cursor, etc.) can discover and call tools at runtime without custom integrations.

---

Quick Start

git clone https://github.com/dmeldrum6/csharp-mcp-tools
cd csharp-mcp-tools
dotnet run --project McpToolServer.Api
# Server is now listening on http://localhost:5000

• JSON-RPC endpoint: POST http://localhost:5000/mcp
• Tool browser: GET http://localhost:5000/mcp/tools
• Health check: GET http://localhost:5000/mcp/health
• Swagger UI: http://localhost:5000/swagger

---

Connecting to Claude Desktop

Add the following to claude_desktop_config.json (typically ~/Library/Application Support/Claude/claude_desktop_config.json on macOS or %APPDATA%\Claude\claude_desktop_config.json on Windows):

{
  "mcpServers": {
    "csharp-tools": {
      "transport": "http",
      "url": "http://localhost:5000/mcp"
    }
  }
}

Restart Claude Desktop. The tools will appear in the tool picker automatically.

---

Tool Reference

Web

Tool	Description	Key Parameters
fetch_webpage	Fetch a URL and return its content as clean plain text (HTML stripped)	url (required), max_chars
fetch_json	Fetch a URL that returns JSON and return the parsed, pretty-printed result	url (required)
post_json	POST a JSON body to a URL and return the response	url, body (required)
check_url	Check the HTTP status of a URL; returns status code, final URL after redirects, and response time	url (required)

Math

Tool	Description	Key Parameters
evaluate_expression	Evaluate a mathematical expression using NCalc (supports trig, log, sqrt, variables)	expression (required)
unit_convert	Convert a value between units using UnitsNet (length, mass, temperature, …)	value, from_unit, to_unit (required)
statistics	Compute descriptive statistics (mean, median, stddev, percentiles) for a list of numbers	values (required)
linear_regression	Fit a simple linear regression y = mx + b to (x, y) data points	x_values, y_values (required)

Text

Tool	Description	Key Parameters
regex_match	Find all regex matches in text; returns positions and captured groups	pattern, text (required), flags
regex_replace	Replace regex matches with a substitution string (supports $1, ${name})	pattern, text, replacement (required)
text_diff	Generate a unified diff between two strings	old_text, new_text (required)
url_encode	URL-encode or decode a string	text (required), decode
text_stats	Count words, sentences, characters, lines; estimate reading time	text (required)
base64	Encode or decode Base64 / Base64-URL	text (required), decode, url_safe
html_to_text	Convert HTML to plain text, preserving links as [text](url)	html (required)

DateTime

Tool	Description	Key Parameters
now	Return the current date and time in multiple formats and timezones	timezone
parse_date	Parse a date string in various formats and return normalized ISO 8601	date (required), timezone
date_add	Add or subtract a duration from a date	date, amount, unit (required)
date_diff	Calculate the difference between two dates	date1, date2 (required), unit
timezone_convert	Convert a datetime from one timezone to another	datetime, from_tz, to_tz (required)
cron_next	Calculate the next N occurrences of a cron expression	expression (required), count, from_date

Crypto

Tool	Description	Key Parameters
hash	Compute a cryptographic hash (MD5, SHA-1, SHA-256, SHA-512)	text (required), algorithm
hmac	Compute an HMAC using a secret key	text, key (required), algorithm
aes_crypt	Encrypt or decrypt a string with AES-256-CBC	text, key (required), mode
generate_uuid	Generate one or more UUIDs (v4)	count
generate_password	Generate a cryptographically secure random password	length, include_symbols

DataFormats

Tool	Description	Key Parameters
parse_csv	Parse a CSV string and return data as JSON	csv (required), delimiter
convert_csv_json	Convert between CSV and JSON array-of-objects	input (required), direction
format_json	Parse, validate, and pretty-print (or minify) a JSON string	json (required), minify
convert_yaml_json	Convert between YAML and JSON	input (required), direction
query_json	Run a JSONPath query against a JSON document	json, path (required)
convert_json_xml	Convert between JSON and XML formats	input (required), direction
format_xml	Parse, validate, and pretty-print (or minify) an XML string	xml (required), minify
query_xml	Run an XPath query against an XML document	xml, xpath (required)

Network

Tool	Description	Key Parameters
dns_lookup	Resolve a hostname to IPs, or look up DNS record types	host (required), type
reverse_dns	Resolve an IP address to a hostname	ip (required)
ping	Ping a host and return round-trip time and packet loss	host (required), count
check_port	Check whether a TCP port is open on a host	host, port (required)

CodeExecution

Tool	Description	Key Parameters
run_csharp	Execute C# via the Roslyn scripting engine; returns stdout and return value	code (required), timeout_seconds, imports
evaluate_js	Evaluate JavaScript using the Jint engine (ECMAScript 2020)	code (required), timeout_seconds
run_sql	Execute SQL against a temporary in-memory SQLite database	query_sql (required), setup_sql, timeout_seconds

FileSystem (sandboxed)

Tool	Description	Key Parameters
read_file	Read a text file from the sandbox	path (required)
write_file	Write text content to a file in the sandbox	path, content (required)
list_files	List files and directories in the sandbox	path
delete_file	Delete a file or empty directory from the sandbox	path (required)
zip_files	Create a ZIP archive from files in the sandbox	files, output_path (required)
unzip_file	Extract a ZIP archive in the sandbox	path, output_dir (required)

Documents

Tool	Description	Key Parameters
image_info	Return image metadata: dimensions, format, color space, file size	url or base64 (required)
image_resize	Resize an image by dimensions or scale factor; returns base64	image, width/height or scale
image_convert	Convert an image to a different format (PNG, JPEG, WebP, …)	image, format (required)
markdown_to_html	Render Markdown text to HTML	markdown (required)
extract_text	Extract readable text from an HTML page URL, stripping nav/ads/boilerplate	url (required)

---

Configuration

All settings live under the McpTools key in appsettings.json:

{
  "McpTools": {
    "Http": {
      "TimeoutSeconds": 30,
      "UserAgent": "McpToolServer/1.0",
      "MaxResponseBytes": 5242880
    },
    "FileSystem": {
      "SandboxPath": "/tmp/mcp-sandbox",
      "MaxFileSizeBytes": 10485760,
      "MaxTotalSandboxBytes": 104857600
    },
    "CodeExecution": {
      "CSharpTimeoutSeconds": 10,
      "JsTimeoutSeconds": 5,
      "SqlTimeoutSeconds": 10
    },
    "Limits": {
      "MaxRequestBodyBytes": 1048576
    }
  }
}

Settings are bound to McpToolsOptions at startup and injected as IOptions<McpToolsOptions>.

---

Security Considerations

File system operations are restricted to the configured sandbox directory. Path traversal attempts (e.g. ../etc/passwd) are rejected before any I/O occurs.

C# execution (run_csharp) uses a text-based blocklist to reject common escape patterns (System.IO, System.Net, System.Reflection, System.Diagnostics.Process, Environment.Exit, AppDomain). This is not an OS-level sandbox — do not expose it to untrusted callers without additional host isolation (containers, gVisor, seccomp).

JavaScript execution (evaluate_js) runs inside Jint, a pure .NET interpreter with no built-in file system or networking. The blocklist also rejects require(), import, fetch(), and XMLHttpRequest.

SQL execution (run_sql) runs against an in-memory SQLite database that is discarded after each request. ATTACH, DETACH, .load, and PRAGMA are blocked.

Transport security: By default the server listens on HTTP. In production, place it behind a reverse proxy (nginx, Caddy) that terminates TLS, enforces authentication, and rate-limits requests.

---

Running Tests

# Unit + non-Integration tests (recommended for CI)
dotnet test --filter "Category!=Integration"

# Full test suite (requires network access)
dotnet test

---

Project Structure

Project	Type	Purpose
McpToolServer.Api	ASP.NET Core Web API	HTTP endpoint, routing, middleware, Swagger
McpToolServer.Tools	Class library	All 52 tool implementations, registry, core interfaces
McpToolServer.Tests	xUnit	Integration and unit tests

See CLAUDE.md for the full developer guide including how to add new tools.