Cuelark Tools

npx add-mcp 'https://tools.cuelark.com/mcp'

Cuelark Tools MCP server

Give Claude, ChatGPT, Cursor, VS Code or any MCP client 15 tools for answers models get wrong: US federal income tax, ABA routing, EIN and ZIP checks, business days with official public holidays, exact decimal math, loan payments, JSON, Base64 and hashes, units and WCAG contrast, plus live checks that links resolve, packages exist and citations are real. India pack included (GSTIN, PAN, IFSC, income tax). Free; an account is optional.

https://tools.cuelark.com/mcp

Streamable HTTP, free, no sign-in needed. 600 requests per minute per IP. The install buttons open the app and ask you to confirm.

Try it live

Connecting…

Calls the real server from your browser with JSON-RPC, exactly as an AI client would. Sample inputs are filled in; edit them and press Run.

Loading tools from tools/list…

Set it up

Claude (claude.ai web, Claude Desktop and Cowork)

Custom connectors are added once to your Claude account and then work in claude.ai, Claude Desktop, Cowork and the mobile apps. Free plans allow one custom connector.

1. Open Customize → Connectors (on claude.ai or in Claude Desktop).
2. Click Add, hover Custom, then choose Web.
3. Name: Cuelark Tools. URL: https://tools.cuelark.com/mcp. Click Continue.
4. Under Authentication choose No sign in, leave request headers empty, then click Add.
5. In a chat, open the tools menu and make sure Cuelark Tools is switched on.

On Team and Enterprise plans an owner adds it under Organization settings → Connectors first; members then click Connect.

Claude Code

claude mcp add --transport http cuelark-tools https://tools.cuelark.com/mcp

ChatGPT (web)

1. Open Plugins in the ChatGPT sidebar on chatgpt.com.
2. Click +, then Add custom MCP server (some accounts show Create custom MCP server).
3. Name: Cuelark Tools. Server URL: https://tools.cuelark.com/mcp. Authentication: No authentication.
4. Tick I understand and want to continue, then Create as a plugin, and install it.
5. In a chat, type @ and pick Cuelark Tools.

If your plan still shows the older flow, turn on Settings → Apps → Advanced settings → Developer mode first, then use Create with the same URL and No authentication. Work workspaces need an admin to allow custom MCP servers.

Cursor

Use Add to Cursor, or add this to ~/.cursor/mcp.json (or .cursor/mcp.json in a project):

{
  "mcpServers": {
    "cuelark-tools": {
      "url": "https://tools.cuelark.com/mcp"
    }
  }
}

VS Code (GitHub Copilot agent mode)

Use Add to VS Code (web link), run this, or add the JSON to .vscode/mcp.json:

code --add-mcp '{"name":"cuelark-tools","type":"http","url":"https://tools.cuelark.com/mcp"}'

{
  "servers": {
    "cuelark-tools": {
      "type": "http",
      "url": "https://tools.cuelark.com/mcp"
    }
  }
}

Other clients

Any client that supports remote Streamable HTTP servers works with the URL. For stdio-only clients, use a bridge: npx -y mcp-remote https://tools.cuelark.com/mcp.

Tools

Tool	What it does
json	Validate and pretty-print or minify JSON (errors give line and column), or convert JSON to YAML or CSV, or CSV to JSON. Web version.
text	Exact text facts models get wrong: word/character/grapheme counts, whether text fits X, SMS, meta title/description or custom:N limits (with a truncated version), letter frequency, case conversion, slugs, JavaScript regex matches and replacements, lorem ipsum, and OpenAI token counts. Web version.
dates	Calendar math: days between dates, add days/weeks/months/years, exact age (with exam cut-offs), business days skipping public holidays (US federal by default; UK, EU, CA, AU, IN, SG, AE), a country's holiday list, and cron schedules in plain English. Web version.
time	Current time anywhere (with DST state and next clock change), convert a wall-clock time between zones, or convert Unix timestamps to and from dates. Accepts IANA zones or common names (ET, PT, UTC, London, IST). Web version.
encode	Base64 and URL encode/decode (UTF-8 safe), MD5/SHA-1/SHA-256/384/512 hashes, new UUID v4/v7 or ULID (or read a ULID's time), and decode a JWT's header and payload without verifying it. Web version.
convert	Unit conversion (imperial and metric: length, weight, volume, area, speed, temperature, data, pressure, energy), color hex/rgb/hsl, WCAG contrast ratio, numbers in words and $ or lakh/crore formats, Markdown to HTML, pixels vs print size at a DPI, and CGPA to percentage (official formulas). Web version.
finance	Monthly loan payment (EMI) with a yearly amortization summary, simple and compound interest (with monthly contributions), percentage math (of, what percent, change, add, subtract), and tax added to or removed from a price at a given rate (VAT, sales tax, or India GST with CGST/SGST/IGST split). Web version.
calculate	Exact decimal arithmetic for an expression (no floating-point drift: 0.1+0.2 = 0.3; + − × ÷ ^ %, sqrt, ln, log, round, min, max, pi), summary statistics for a list of numbers, rounding with a chosen mode, and adult BMI from lb/in or kg/cm. Web version.
income_tax	Estimate income tax from official tables. us_federal: 2025 or 2026 IRS brackets, standard deduction (with 65+/blind extras) or itemized, by filing status. india: FY 2025-26 or 2026-27, new vs old regime with 87A rebate, surcharge and cess. Each answer cites its source. Web version.
validate	Check an identifier's format and check digit: US ABA routing number, EIN, SSN (format rules only), ZIP; card numbers (Luhn) and IBAN; India GSTIN, PAN, IFSC, UPI ID, Aadhaar (Verhoeff) and PIN code. Proves a value is well formed, not that it's registered. Nothing is stored. Web version.
ifsc_lookup	Bank, branch, address, MICR and NEFT/RTGS/IMPS/UPI support for an Indian IFSC code, from RBI's published lists via Razorpay's IFSC dataset. Web version.
verify_links	Check up to 20 URLs live: HTTP status, redirects, final URL, page title and canonical, and optionally whether each page contains a quote. Respects robots.txt and refuses private addresses. Web version.
package_check	Does this package exist (catches invented names)? Latest version, deprecation, license, repository, last publish, downloads, and the newest version matching a range. Ecosystems: npm, pypi, crates. Web version.
verify_citation	Check that a paper exists and get its canonical metadata (title, authors, year, venue, DOI link, retraction flag) by DOI, arXiv id, or title plus author. Uses Crossref, OpenAlex and arXiv. No abstracts. Web version.
ui_component_lookup	Search the ui.cuelark.com shadcn/ui registry (React components, blocks, themes) and get the shadcn CLI install command for each match. Web version.

Privacy

• Inputs and results are not logged or stored. Each request is computed and forgotten; there are no sessions.
• With an API key or OAuth sign-in, auth.cuelark.com counts calls per key per day for your usage chart. It never sees your inputs.
• Only text and numbers are accepted. There are deliberately no image or PDF tools here: those run only in your browser at tools.cuelark.com, so files are never uploaded anywhere.
• Rate limiting counts requests per IP address in Cloudflare's rate limiter; the IP is not stored with any input.
• ui_component_lookup reads the public ui.cuelark.com registry; your query is matched on our side and is not sent on.

API keys and sign-in (optional)

Anonymous use stays free. If you want your own limit and usage history, sign in once with a Cuelark account (email code, no password). One account works across tools.cuelark.com and future Cuelark products.

• OAuth (Claude, ChatGPT, VS Code, Cursor): choose OAuth instead of No authentication when you add the server. The client finds /.well-known/oauth-protected-resource, opens auth.cuelark.com for you to sign in and approve, and gets a 15-minute token it refreshes on its own. Revoke access any time under Connected apps on your dashboard.
• API key: create one on the dashboard with Tools ticked. It is shown once and stored only as a hash. Send it as a header: Authorization: Bearer cue_….

curl -s https://tools.cuelark.com/mcp \
  -H "Authorization: Bearer cue_YOUR_KEY" \
  -H "content-type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

A wrong, revoked or expired credential gets a 401 instead of silently falling back to anonymous, so you notice. Remove the header to go back to the free tier.

Example prompts

• "What is the 2026 federal income tax on $95,000 for a single filer with the standard deduction?"
• "Is 021000021 a valid ABA routing number, and which Federal Reserve district is it?"
• "Add 10 business days to 2026-11-20 in the US, skipping federal holidays."
• "Check these 5 links still resolve and that the npm package zod-mini exists."
• "Is this GSTIN valid: 27AAPFU0939F1ZV?"