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Halowerk MCP

Pay for 70 allowlisted APIs over MCP with USDC on Base, spending caps, dry runs, and no account.

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Install Halowerk MCP

Pick your client, then add it in one click or paste the config.

STDIONode.js
~/Library/Application Support/Claude/claude_desktop_config.json
claude_desktop_config.json
{
  "mcpServers": {
    "halowerk-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "halowerk-mcp"
      ],
      "env": {
        "HALOWERK_PRIVATE_KEY": "YOUR_VALUE_HERE",
        "HALOWERK_MAX_PREIS_USDC": "YOUR_VALUE_HERE",
        "HALOWERK_BUDGET_USDC": "YOUR_VALUE_HERE",
        "HALOWERK_TROCKEN": "YOUR_VALUE_HERE",
        "HALOWERK_MODUS": "YOUR_VALUE_HERE"
      }
    }
  }
}

Settings → Developer → Edit Config, merge this into mcpServers, then fully quit and reopen Claude Desktop.

Values are written into the snippet above so you can paste it as is. They never leave your browser.

We couldn’t confirm it starts correctly

We ran the install command but it didn't respond within our test window — this can mean a slow first-time install rather than a real problem.

npx -y halowerk-mcp

No response to initialize.

This is an experimental automated check and can have false negatives — missing environment variables, a slow cold install, etc. It doesn’t necessarily mean something’s wrong. Last checked 2d ago.

Overview

The halowerk-mcp MCP server exposes 70 paid APIs as MCP tools and settles calls with USDC on Base. It includes free catalogue and price tools, configurable per-call and session limits, and a dry-run mode before payment. Use it when an agent needs repeated access to the listed services without creating an account, while keeping payment targets and spending bounded.

Use cases

  • Browse available paid APIs before connecting a wallet
  • Validate model output after each response
  • Audit dependencies for CVEs or license issues
  • Inspect TLS chains, JWTs, or webhook signatures
  • Process repeated invoices or document comparisons

Key features

  • 70 catalogue-based paid API tools
  • USDC payments on Base via x402
  • Per-call and per-session spending caps
  • Dry-run price and call planning
  • Allowlisted HTTPS payment hosts
  • Hero, gateway, and all tool modes

Security & health

What it can reach and how reliably it runs — from our own checks, not the maintainer’s claims.

ActiveLast checked 2d ago

Recent health check succeeded.

7/7 checks healthy over the last 40d

Supply-chain signal

No high-severity advisories surfaced by our automated scan.

Critical 0High 0Medium 0Low 0

Scanned 14d ago via OSV.dev · halowerk-mcp (npm)

Adoption & maintenance

Factual signals from GitHub, npm, and our automated checks — not a rating.

npm downloads219Package downloads in the last 30 days.
Last commit2mo agoMost recent push to the default branch.
Install checkInconclusiveDidn't respond in our test window — often a slow first install.
Directory activity1 viewsConfig copies, upvotes, and views on AllMCPs.

How Halowerk MCP works

What halowerk-mcp does

The halowerk-mcp MCP server presents a catalogue of 70 paid APIs as callable MCP tools. Calls use x402 payment authorization with USDC on Base; there is no account, subscription, card, or invoice flow. The package signs authorization for the exact amount and relies on a third party to submit the transaction.

Two tools are free to use without a wallet. halowerk_katalog lists the available services and their prices, while halowerk_preis estimates the cost of a planned call. Paid responses include the amount paid, remaining session budget, and transaction hash.

How it works

The halowerk-mcp MCP server reads a private key from HALOWERK_PRIVATE_KEY when payment is needed. It does not create or store keys, move funds for other purposes, or require ETH for gas. Payment uses EIP-3009 transferWithAuthorization, so a wallet with USDC on Base can have an ETH balance of zero.

Spending controls run before signing. HALOWERK_MAX_PREIS_USDC limits the price of one call, and HALOWERK_BUDGET_USDC limits total spending for the session. Services with tiered pricing are checked against their maximum possible charge rather than only their minimum price. Services without a known ceiling require unbegrenzt_erlauben: true.

Three modes control how many service tools appear in the MCP tool list:

  • hero exposes 12 selected services plus the two free tools.
  • gateway exposes search, schema-description, and execution meta-tools plus the free tools.
  • all exposes all 70 services plus the free tools.

Setup and configuration

Run the package through npx as an MCP stdio server. The README provides configurations for Claude Desktop, Cursor, and Cline. A wallet is not needed to browse the catalogue or inspect prices. For paid calls, place a small amount of USDC on Base in a separate wallet and pass its private key through the MCP environment configuration.

Supported settings include:

  • HALOWERK_PRIVATE_KEY: key used to sign paid call authorizations.
  • HALOWERK_MAX_PREIS_USDC: per-call ceiling; the default is 0.05.
  • HALOWERK_BUDGET_USDC: per-session ceiling; the default is 1.00.
  • HALOWERK_TROCKEN: enables dry-run behavior, returning price and call plan without paying.
  • HALOWERK_MODUS: selects hero, gateway, or all; hero is the default.

Tools and capabilities

The catalogue contains recurring text-in/text-out utilities such as cost estimation, output and argument validation, state storage, CVE and license checks, TLS-chain inspection, JWT verification, webhook-signature checking, document comparison, web archiving, and invoice auditing. The exact services available are determined by the shipped catalogue.

In gateway mode, halowerk_suche searches services by description, halowerk_beschreibe returns an input schema, and halowerk_rufe_auf executes a catalogue service by name.

Limitations and notes

Only the ten hosts embedded in the build-time catalogue can receive payments. The target must match an allowlisted host exactly, use HTTPS, and not resolve through redirects to another host. IP addresses, localhost, and private network ranges are rejected before signing. The execution tool accepts a catalogue tool name rather than an arbitrary URL.

The catalogue is bundled with the package and is not fetched during runtime. It must be regenerated from live services before republishing when prices or services change. Keep the private-key wallet separate and funded only with an amount you are prepared to lose, because the key is reachable by the model-driven process using the MCP configuration.

The package is licensed under MIT.

Read the full README View source on GitHub

Reviews

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Frequently Asked Questions about Halowerk MCP

halowerk-mcp is an MCP server that connects agents to 70 paid APIs through a fixed catalogue, using USDC on Base for x402 payments. Its main tools list services, estimate prices, search and describe catalogue entries, and execute selected API calls with per-call and session spending limits.

Install it as an MCP stdio server with `npx -y halowerk-mcp` in an MCP client configuration. You can use the catalogue and price tools without configuring a wallet.

Pay by setting `HALOWERK_PRIVATE_KEY` to a wallet key holding USDC on Base. The server signs x402 authorization for the call amount, while a third party submits the transaction. ETH is not required for gas, but the key should belong to a separate, limited-funds wallet.

Set `HALOWERK_MAX_PREIS_USDC` for the maximum cost of one call and `HALOWERK_BUDGET_USDC` for the session total. The defaults are 0.05 and 1.00 USDC. Set `HALOWERK_TROCKEN` to use dry runs that return a plan without paying.

Yes, halowerk-mcp works with Cursor through its `mcp.json` configuration. Run it with the `npx -y halowerk-mcp` command and add wallet and spending environment variables only if paid calls are required.

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