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Castov
MODEL CONTEXT PROTOCOL • STDIO JSON-RPC 2.0 • V1.4.0

Castov MCP Server

Give Claude Desktop, Cursor, Windsurf, and VS Code Copilot deterministic local execution superpowers. 10 hardened, read-only developer tools with zero telemetry and zero cloud roundtrips.

Glama Certified: Grade A Security & Qualitynpm: castov@1.4.0GitHub Repository (MIT)

Quick Setup for AI Coding Agents

Anthropic Official Zero-Telemetry Stdio

~/Library/Application Support/Claude/claude_desktop_config.json (macOS) • %APPDATA%\Claude\claude_desktop_config.json (Windows)

{
  "mcpServers": {
    "castov": {
      "command": "npx",
      "args": ["-y", "castov@latest", "mcp"]
    }
  }
}
Restart Claude Desktop after saving. Look for the 🔨 hammer icon showing 10 Castov local tools.

Interactive MCP Live Playground

Interactive JSON-RPC 2.0 Inspector

Select any tool below and edit the payload to inspect the exact stdio JSON-RPC messages exchanged with Claude & Cursor.

100% Client-Side Simulation
Agent Request (stdio stdin)
tools/call
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "castov_cidr",
    "arguments": {
      "cidr": "10.240.0.0/22"
    }
  }
}
Castov MCP Output (Decoded Result)
{
  "cidr": "10.240.0.0/22",
  "inputIp": "10.240.0.0",
  "networkAddress": "10.240.0.0",
  "broadcastAddress": "10.240.3.255",
  "subnetMask": "255.255.252.0",
  "wildcardMask": "0.0.3.255",
  "firstUsableHost": "10.240.0.1",
  "lastUsableHost": "10.240.3.254",
  "usableHosts": 1022,
  "totalAddresses": 1024
}

Hardened Security Annotations

Every MCP tool declares strict readOnlyHint: true, destructiveHint: false, and openWorldHint: false annotations, using execFileSync argument arrays to eliminate shell injection.

Zero LLM Arithmetic Hallucinations

Eliminate AI errors on CIDR subnet masks, RFC 3021 point-to-point ranges, IANA Daylight Saving Time shifts, Snowflake bit-shifting, and Cron schedule predictions.

100% Local & Air-Gapped

JWT tokens, .env files, and cryptographic secrets never leave your machine. Dual-framing stdio supports both Content-Length and ndjson transports.

Complete Tool Specification

Available MCP Tools

All tools include comprehensive JSON Schema validation, explicit type constraints, and deterministic JSON output.

castov_port

Port & Process Inspector

readOnlyHint: true

Identifies standard service registrations for TCP/UDP ports (1–65535) and inspects active local processes listening on the port across Linux, macOS, and Windows.

Example Agent Prompt:“Check if port 3000 is currently in use and tell me which process owns it.”
Input Schema:{ port: number }
castov_cidr

IPv4 CIDR & Subnet Calculator

readOnlyHint: true

Calculates exact IPv4 network address, subnet mask, wildcard mask, broadcast address, first/last usable host IPs, and total host capacity (including RFC 3021 /31 and /32).

Example Agent Prompt:“Calculate the usable IP range, broadcast address, and wildcard mask for 10.240.0.0/22.”
Input Schema:{ cidr: string }
castov_detect_id

Distributed ID & Timestamp Decoder

readOnlyHint: true

Detects and extracts embedded creation timestamps from UUIDv7, UUIDv1/v4, ULID, MongoDB ObjectId, and Discord/Twitter Snowflake IDs.

Example Agent Prompt:“Decode when this ID was generated: 018f3a9c-6d20-7000-8000-010203040506”
Input Schema:{ id: string }
castov_timestamp

Unix Epoch & ISO 8601 Converter

readOnlyHint: true

Converts Unix epoch timestamps (seconds or milliseconds) or ISO date strings into UTC, ISO 8601, local time, and relative time offsets.

Example Agent Prompt:“Convert Unix timestamp 1760868000 to ISO 8601 and UTC.”
Input Schema:{ value: string }
castov_uuid

Cryptographic UUIDv4 / UUIDv7 / ULID Generator

readOnlyHint: true

Generates cryptographically secure RFC 9562 UUIDv4, time-ordered UUIDv7, or lexicographically sortable ULID identifiers in batches up to 50.

Example Agent Prompt:“Generate 5 time-ordered UUIDv7 identifiers for my database migration.”
Input Schema:{ format?: 'uuidv4' | 'uuidv7' | 'ulid', count?: number }
castov_cron

Cron Schedule Explainer & Next Run Predictor

readOnlyHint: true

Parses 5-field POSIX cron expressions into human-readable descriptions and computes the exact next 5 execution timestamps in any IANA timezone.

Example Agent Prompt:“When are the next 5 runs for '*/15 9-17 * * 1-5' in America/New_York?”
Input Schema:{ expression: string, timezone?: string }
castov_timezone

IANA Timezone Converter

readOnlyHint: true

Converts dates, times, or timestamps accurately between any two IANA timezones with automatic DST offset calculation.

Example Agent Prompt:“Convert 2026-06-15 14:30 from Europe/London to Asia/Tokyo.”
Input Schema:{ dateTime: string, fromZone: string, toZone: string }
castov_secret

CSPRNG Cryptographic Secret Generator

readOnlyHint: true

Generates high-entropy cryptographic secrets (16 to 128 bytes) in Hex, Base64, Base64URL, and ready-to-use .env key formats via Node.js crypto.randomBytes.

Example Agent Prompt:“Generate a 256-bit cryptographic secret for my AUTH_SECRET and JWT_SECRET.”
Input Schema:{ bytes?: number }
castov_jwt_decode

Offline JWT Header & Claims Inspector

readOnlyHint: true

Decodes JWT header and payload claims locally, formatting issued-at (iat), not-before (nbf), and expiration (exp) timestamps without transmitting tokens over the network.

Example Agent Prompt:“Inspect the payload claims and expiration status of this JWT token.”
Input Schema:{ token: string }
castov_hash

Cryptographic Digest Calculator

readOnlyHint: true

Computes deterministic cryptographic digests (MD5, SHA-1, SHA-256, SHA-384, SHA-512) in both hexadecimal and Base64 encodings.

Example Agent Prompt:“Compute the SHA-256 hex and Base64 digest of this webhook payload.”
Input Schema:{ text: string, algorithm?: 'md5' | 'sha1' | 'sha256' | 'sha384' | 'sha512' }
castov_scan_secrets

In-Memory Secret & Credential Leak Scanner

readOnlyHint: true

Audits code snippets, .env files, or terminal logs in-memory for leaked AWS keys, GitHub PATs, Stripe live keys, OpenAI keys, Slack tokens, and PEM private keys with redacted output.

Example Agent Prompt:“Scan this configuration snippet for any accidentally hardcoded API keys before I commit.”
Input Schema:{ content: string }

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