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String Utility Belt

Official registry AI and agents

MCP server exposing String Utility Belt's utilities and pipelines as tools for AI agents.

Source code Website Documentation

What can you do with String Utility Belt?

  • Pipelines — add, reorder (drag and drop), duplicate, disable/solo steps; undo/redo; per-step
  • Share and save — pipelines (and optionally the input) as compressed #/p/… links, a named
  • Magic — detects the input's format (base64, JWT, gzip, JSON, …) and suggests or appends the
  • Input/output — file upload (text and binary), fetch-a-URL via the Worker proxy, input history,
  • Engine — runs in a Web Worker with cancellation, adaptive debounce, a chunked mode for
  • App — command palette (Ctrl+K), keyboard shortcuts (?), fuzzy utility search with

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

NPM package @string-utility-belt/mcp
Claude Code 
claude mcp add string-utility-belt -- npx -y @string-utility-belt/mcp@1.10.2
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "string-utility-belt": {
            "command": "npx",
            "args": [
                "-y",
                "@string-utility-belt/mcp@1.10.2"
            ]
        }
    }
}

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. String Utility Belt
  2. Use it from your agent, terminal or editor
  3. Features
  4. Using the app
  5. Development
  6. Other surfaces
  7. Support the project
  8. Contributing
  9. License

String Utility Belt

stringutilitybelt.com · Usage guide · All utilities · Integrations

Chain string transformations into visual pipelines with live, per-step previews. 246 utilities — encodings, hashes, ciphers, compression, data formats (JSON/YAML/TOML/CSV/XML), line and text operations, analysis, generators, web/dev helpers, numbers, dates and colours — all running client-side, with the same engine available as a CLI, an HTTP API, an MCP server, a browser extension and a VS Code extension.

Use it from your agent, terminal or editor

Every utility also runs on your own machine, outside the browser:

# Give Claude Code (or any MCP client) exact hashing, encoding and decoding instead of a guess
claude mcp add subelt -- npx -y @string-utility-belt/mcp

# Pipe text through a pipeline from the shell
echo 'eyJ1c2VyIjoiYWRhIn0=' | npx subelt base64_decode json_pretty

Features

  • Pipelines — add, reorder (drag and drop), duplicate, disable/solo steps; undo/redo; per-step previews, diffs, timings and error policies (pass through / stop / empty); conditional steps; parallel branches with concat/zip/json/pick merges; macros (collapse a sub-chain into one step); "run on each" steps (run a sub-chain on every line, delimited piece, JSON array element or object value).
  • Share and save — pipelines (and optionally the input) as compressed #/p/… links, a named pipeline library with JSON import/export, a preset gallery, an embeddable #/embed/… widget.
  • Magic — detects the input's format (base64, JWT, gzip, JSON, …) and suggests or appends the decoding step; "decode until stable" mode.
  • Input/output — file upload (text and binary), fetch-a-URL via the Worker proxy, input history, side-by-side and diff views, hex view for bytes, syntax highlighting, stats bar, smart download names, copy-as (raw / JSON literal / hex / base64).
  • Engine — runs in a Web Worker with cancellation, adaptive debounce, a chunked mode for multi-MB inputs and a preview-first-64 KB option; custom JavaScript steps run in a sandboxed, network-less iframe + worker, and are quarantined when they arrive from someone else's link.
  • App — command palette (Ctrl+K), keyboard shortcuts (?), fuzzy utility search with favourites/recents and type-aware badges, light/dark themes, per-utility doc pages with a live playground, installable PWA with offline support and an OS share target, i18n scaffold.

Using the app

Open stringutilitybelt.com — nothing to install, and every transformation runs in your browser (see the privacy policy for the few features that contact the server). The site sets no cookies and runs no tracking scripts: Cloudflare Web Analytics counts page views without cookies, the site's own server counts clicks on sponsor and tool links, utilities added, and editor opens and runs by id alone, neither ever receives what you paste, and the site's Content-Security-Policy blocks scripts from anywhere else. The how-to guide lives in the app itself: click Docs in the header, or go to /docs/. Each utility's settings and examples are on its own page, listed at /utilities/.

From a terminal, the same engine is one command away:

echo -n hello | npx subelt trim base64_encode hash   # SHA-256 of the base64

Development

Requires Node.js 20.19+ or 22.12+.

git clone https://github.com/String-Utility-Belt/string-utility-belt.git
cd string-utility-belt
npm ci
npm run dev          # generates the utility manifest, then starts Vite
npm test             # Vitest (unit, component, golden-example and property tests)
npm run lint
npm run typecheck
CommandWhat it does
npm run genRegenerate src/utilities/_generated/* (run automatically before dev/build)
npm run buildProduction build of the web app
npm run check:bundleEnforce the entry-chunk budget in bundle-budget.json
npm run build:seoPre-render utility pages, sitemap, RSS and OG images into dist/ (build:seo:fast skips OG images)
npm run build:sitebuild + build:seo
npm run build:toolsBuild packages/* (core, CLI, MCP server, browser extension, VS Code extension)
npm run test:e2ePlaywright end-to-end tests against a production build
npm run benchLarge-input benchmarks (vitest bench)
npm run deploybuild:site, then wrangler deploy (Cloudflare Workers: static assets + /api/*) — releases normally deploy from CI
npm run release -- planWhat a release from HEAD would ship, and at which versions (RELEASING.md)
npm run readme:demoRe-record this README's demo GIF from the production build (after npm run build; needs ffmpeg)

Other surfaces

SurfaceWhereNotes
Core librarypackages/coreFramework-free engine + all utilities
CLIpackages/cli`echo -n hello \subelt base64_encode`
MCP serverpackages/mcpUtilities and pipelines as agent tools over stdio
HTTP APIworker/POST /api/run, GET /api/utilities[/:id] (CORS, rate-limited)
Browser extensionpackages/extensionMV3; context menu "run on selection"
VS Code extensionpackages/vscodeTransform selection, run a share link

Support the project

String Utility Belt is free, open source and has no paid tier. If it saves you time, you can support its development through GitHub Sponsors: it pays for hosting and keeps new utilities, presets and fixes coming. Companies can also sponsor a page on the site.

Contributing

Contributions are welcome — bug reports, utility ideas and pull requests. Start with CONTRIBUTING.md (setup, adding a utility, PR checklist) and the Code of Conduct. CLAUDE.md is the detailed architecture reference.

Found a security issue? Please report it privately — see SECURITY.md.

License

MIT

Frequently asked questions

What is String Utility Belt?

MCP server exposing String Utility Belt's utilities and pipelines as tools for AI agents.

How do I install String Utility Belt?

It runs on your machine. In Claude Code: claude mcp add string-utility-belt -- npx -y @string-utility-belt/mcp@1.10.2. For other clients, paste the JSON configuration from this page into their MCP settings.

Does String Utility Belt need an API key?

Its registry entry lists no required key or secret. Some features may still need an account with the service it connects to.

Is String Utility Belt open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains String Utility Belt?

It is published by String-Utility-Belt. AI.tn lists it but does not maintain or endorse it.

From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.