Deterministic local tooling for Claude Desktop, Cursor, Windsurf, and Local LLMs via the Model Context Protocol (MCP) — backed by a high-performance CLI, Docker image, IDE extension, and 61 client-first browser utilities.
Modern AI agents and developer workflows suffer from two critical flaws:
- Agent Hallucinations on Exact Operations: LLMs frequently blunder arithmetic for CIDR network masks, time zone offsets, epoch milliseconds, and cryptographic key derivations.
- Data & Secret Leakage: Sending system logs, environment variables, or tokens to third-party cloud APIs presents unacceptable security hazards.
Castov solves both. It acts as an in-situ Execution Layer for developer environments. It provides deterministic, offline, and instant utilities delivered directly to your terminal, editor, Docker containers, and AI agents through the Model Context Protocol (MCP).
Everything runs 100% locally. No external analytics, no telemetry, and zero cloud roundtrips.
Castov ships with a built-in, production-grade JSON-RPC 2.0 stdio MCP server supporting both Content-Length framed and ndjson stream protocols.
Add Castov to your claude_desktop_config.json:
- macOS:
~/Library/Application Support/Claude/claude_desktop_config.json - Windows:
%APPDATA%\Claude\claude_desktop_config.json - Linux:
~/.config/Claude/claude_desktop_config.json
{
"mcpServers": {
"castov": {
"command": "npx",
"args": ["-y", "castov", "mcp"]
}
}
}Go to Settings → Features → MCP Servers → Add New MCP Server:
- Name:
castov - Type:
command - Command:
npx -y castov mcp
Alternatively, add to your project's .cursor/mcp.json:
{
"mcpServers": {
"castov": {
"command": "npx",
"args": ["-y", "castov", "mcp"]
}
}
}| MCP Tool | Capability | Example Agent Prompt |
|---|---|---|
castov_port |
Identifies listening services, protocol mappings, and inspects process collision | "Why is port 3000 busy and what service uses it?" |
castov_cidr |
Calculates IPv4 subnet masks, wildcard, broadcast, and usable host count | "Calculate usable IP range and subnet mask for 10.240.0.0/22" |
castov_detect_id |
Decodes embedded creation timestamps from UUIDv7, ULID, ObjectId, Snowflake | "When was this MongoDB ObjectId or Snowflake ID created?" |
castov_timestamp |
Bidirectional epoch conversion to ISO 8601, UTC, and localized representations | "Convert 1713456789 to human UTC and ISO format" |
castov_cron |
Parses 5-field cron schedules into plain English and computes next 5 runs | "Explain cron 0 9 * * 1-5 and show the next 5 runs in America/New_York" |
castov_timezone |
Converts timestamps across IANA time zones with DST transition warnings | "Convert 2026-03-29 14:30 from America/New_York to Europe/Paris" |
castov_secret |
Generates CSPRNG 256-bit Hex, Base64URL, API keys, and sortable UUIDv7 secrets | "Generate a 256-bit cryptographic secret for AUTH_SECRET and JWT_SECRET" |
castov_jwt_decode |
Decodes JWT headers, payloads, and exp status offline with zero network calls |
"Decode this JWT offline and check if it is expired" |
castov_hash |
Computes SHA-256/384/512, SHA-1, MD5 digests and Base64/Base64URL encodings | "Compute the SHA-256 hex digest and Base64URL encoding of this webhook payload" |
castov_scan_secrets |
Audits code snippets, git diffs, or .env blocks for leaked API keys & private keys |
"Scan this git diff for any accidentally hardcoded AWS, Stripe, or OpenAI keys" |
Castov is available everywhere modern engineering happens:
Run instantly without installation:
npx castov --helpOr install globally:
npm install -g castov
castov --helpLightweight Alpine Linux container (node:20-alpine) running under a non-root node user:
# Run one-off command
docker run --rm castovdev/castov:latest uuid --v7
# Interactive diagnostic shell
docker run -it --rm castovdev/castov:latestInstall natively via Brew:
brew tap castovdev/castov
brew install castov
# Verify installation
castov --versionInstall the official extension directly within your editor:
- VS Code Marketplace: Search
Castovor installCastov.castov-vscode - Open VSX Registry: Available for Cursor, Windsurf, VSCodium:
castov/castov-vscode
# Command line installation
code --install-extension Castov.castov-vscodeAutomate security scans, secret leakage audits, and environment checks in your GitHub workflows:
- name: Run Castov Secret Scanner
uses: castovdev/castov-action@v1.0.0
with:
command: 'scan .'castov <command> [options]
Inspect what process is occupying a port or kill it cleanly:
# Inspect service and protocol
castov port 3000
# Inspect active process PID and terminate it immediately
castov port 3000 --killGenerate high-entropy keys for .env, NEXTAUTH_SECRET, JWT signing, and API authentication:
castov secret
castov secret --len 64Calculate network masks, wildcard masks, and usable host ranges with zero external lookups:
castov cidr 192.168.1.0/24
castov cidr 10.0.0.0/16Recursively scan local directories for committed or uncommitted API tokens (AWS, Stripe, OpenAI, GitHub, Private Keys):
castov scan .Pipe terminal crashes or paste error stack traces for instant, deterministic remediation:
castov fix "Error: listen EADDRINUSE: address already in use :::8080"
npm run build 2>&1 | castov fixBootstrap .cursorrules or CLAUDE.md with hardened engineering practices:
castov rules nextjs --write
castov rules fastapi
castov rules rustExtract metadata and epoch timestamps from any modern distributed identifier:
castov detect 018e3a2b-8a5c-7b00-9821-654321abcdef
castov detect 507f1f77bcf86cd799439011
castov ts 1713456789In addition to the CLI and MCP Server, Castov provides 63 client-side web tools accessible at castov.com:
| Category | Featured Tools |
|---|---|
| Security & Privacy | Steganography Env Vault, Client-Side Secret Scanner, Zero-Knowledge Env Vault, Hash Generator (SHA-256/512/MD5), JWT Decoder, Base64 Encoder/Decoder, UUID v4/v7 Generator. |
| Networking & DevOps | EADDRINUSE Port Inspector, IPv4 CIDR Calculator, Dockerfile Visualizer, P2P Ghost Tunnel, Fetch Mock Generator, API Load Tester, DNS & Header Inspector. |
| Data & Architecture | JSON to TypeScript Type Generator, 3D JSON Galaxy, Interactive JSON Formatter & Viewer, SQLite In-Browser Fiddle, Line-by-Line Diff Checker, AST Conflict Telepathy. |
| Frontend & UI | Glassmorphism CSS Studio, App Mockup Generator, High-Resolution Code-to-Image Renderer, Favicon Generator, GitHub Profile README Builder. |
| Time & Scheduling (25+ Tools) | Unix Timestamp Converter, Epoch Converter, ISO 8601 & RFC 3339 Parser, Timezone Converter & Simulator, Plain-English Cron Generator & Explainer, World Clock, Business Hours Matrix, Milliseconds to Date. |
Engineering tools should never leak your IP, company secrets, or code snippets.
- 0 Analytics or Tracking Cookies: No PostHog, Google Analytics, or third-party telemetry scripts.
- Offline First: All cryptographic operations rely on the browser and runtime's native
SubtleCrypto/ Web Crypto API. - Air-Gap Compatible: Both the CLI, Docker image, and web application can run in offline and restricted intranet environments.
Castov is built with Next.js 16 (App Router), TypeScript (Strict), and Tailwind CSS v4.
# 1. Clone repository
git clone https://github.com/castovdev/castov.git
cd castov
# 2. Install dependencies
npm install
# 3. Setup local environment
cp .env.example .env.local
# 4. Start development server
npm run dev
# 5. Build CLI and Web applications
npm run buildTo run tests across packages:
npm run testCastov is open-source software licensed under the MIT License — Copyright © 2026 Abdelmalik Benidir / Castov (castov.com). Free for personal, commercial, and enterprise usage.