stringbox-mcp 1.2.0

StringBox

A high-performance .NET 10 MCP server that gives AI coding agents 88 text, JSON, encoding, hashing, and crypto utility functions. Designed to eliminate the token waste agents create with ad-hoc Python scripts and inline transformations.

Why

Agents waste tokens on trivial operations. They either burn context explaining Python one-liners or hallucinate base64 output. StringBox solves this by exposing deterministic functions through MCP.

Only two MCP tools are registered -- run and help. This keeps per-message token overhead under 100 tokens regardless of how many functions exist. Most function names are self-explanatory (base64_enc, snake_case, md5) so agents call them without consulting help first.

Install

.NET Global Tool

dotnet tool install -g stringbox-mcp

Native Binary

Download from GitHub Releases -- no .NET runtime required.

MCP Configuration

Claude Code

claude mcp add stringbox-mcp -- stringbox-mcp

Claude Desktop / Cursor / VS Code

Add to your MCP config file:

{
  "mcpServers": {
    "stringbox": {
      "command": "stringbox-mcp"
    }
  }
}

How It Works

Tool 1: run(fn, input, opts?)

Executes a named function. The tool description contains a compact list of all 88 function names (~160 tokens). An agent sees snake_case in the list, knows what it does, and calls run("snake_case", "myVariableName") directly.

• input is always a string (the primary data to operate on)
• opts is an optional JSON object with named parameters
• output is always a string (the result)
• errors return {"error": "message", "usage": "expected usage"}

Tool 2: help(topic?)

On-demand documentation. Only called when the agent needs parameter details for complex functions.

• help() -- category overview
• help("json") -- all functions in that category
• help("regex_replace") -- detailed docs with parameters and examples

Help is also available via run: run("help", "json") or run("help:json", "").

Examples

run("snake_case", "myVariableName")                          -> "my_variable_name"
run("base64_enc", "hello world")                             -> "aGVsbG8gd29ybGQ="
run("sha256", "hello")                                       -> "2cf24dba5fb0a30..."
run("json_query", '{"users":[{"name":"Alice"}]}',
    {"path": "$.users[0].name"})                             -> "\"Alice\""
run("regex_replace", "foo123bar",
    {"pattern": "\\d+", "replacement": "NUM"})               -> "fooNUMbar"
run("hmac", "message",
    {"algorithm": "sha256", "key": "secret"})                -> "8b5f48702995c159..."
run("uuid", "")                                              -> "550e8400-e29b-41d4-..."
run("json_flatten", '{"a":{"b":1,"c":{"d":2}}}')            -> '{"a.b":1,"a.c.d":2}'
run("aes_encrypt", "secret data",
    {"key": "<64-char hex>"})                                -> '{"ciphertext":"...","nonce":"...","tag":"..."}'

Function Reference

Case (8)

All case functions auto-detect the source convention (camel, snake, kebab, spaces, mixed, consecutive uppercase like XMLParser) and convert correctly.

String (19)

Regex (6)

All regex functions use a 5-second timeout to prevent catastrophic backtracking.

Encoding (13)

Hash (11)

JSON (13)

Uses JsonPath.Net for JSONPath queries per RFC 9535.

Text (7)

Crypto (11)

CLI

StringBox also ships as a standalone CLI tool:

dotnet tool install -g sbox

Building from Source

git clone https://github.com/Jabe/StringBox.git
cd StringBox
dotnet build
dotnet test

Native AOT

dotnet publish src/StringBox.Cli -c Release -r osx-arm64 --self-contained -p:PublishAot=true
dotnet publish src/StringBox.Mcp -c Release -r osx-arm64 --self-contained -p:PublishAot=true

Supported RIDs: osx-arm64, linux-x64, win-x64.

Architecture

StringBox.sln
├── src/
│   ├── StringBox/              # Core library (88 pure functions, zero dependencies on MCP)
│   │   └── Functions/          # One file per category
│   ├── StringBox.Cli/          # CLI tool (assembly: sbox)
│   └── StringBox.Mcp/          # MCP server (assembly: stringbox-mcp)
│       └── Tools/              # run + help MCP tool definitions
└── tests/
    └── StringBox.Tests/        # 226 tests, one file per category

The core library is separate from the MCP server so the functions can be used as a NuGet package independently:

dotnet add package StringBox

var registry = new FunctionRegistry();
var result = registry.Execute("snake_case", "myVariableName", null);
// "my_variable_name"

License

MIT