ASPERN: counterparty checks for agents

ASPERN

What the chain records about an address before you pay it, and whether a payment fits it.

ASPERN is an independent, read-only evidence service for autonomous agents and the people who allocate capital to them. It reads public on-chain and venue data and answers two kinds of question:

• Before paying or hiring an agent: who pays this address, whether it pays them back, whether it delivers, whether its service answers, when it was last paid.
• Before depositing into a vault: what it holds, who controls it, what a withdrawal of a given size would actually return, and which readings are missing.

Every figure carries the time it was read and its source. A figure we could not measure is named as not measured, never shown as zero.

This repository holds the public documentation: how to connect, what each tool and endpoint does, what it costs, and the server's registry entry. The service itself is hosted; its source code is not published.

• Website: https://aspern.org
• MCP server: https://aspern.org/mcp (streamable HTTP)
• REST API: https://aspern.org/api/v1 · OpenAPI: https://aspern.org/api/v1/openapi.json
• Agent card: https://aspern.org/.well-known/agent-card.json
• Methodology: https://aspern.org/methodology

Connect

No install. The free tools need no key.

Claude Code

claude mcp add --transport http aspern https://aspern.org/mcp

Claude Desktop / claude.ai: Settings → Connectors → Add custom connector → https://aspern.org/mcp.

Cursor (.cursor/mcp.json) and other clients that take a URL:

{

"mcpServers": { "aspern": { "url": "https://aspern.org/mcp" } } }

VS Code (.vscode/mcp.json):

{

"servers": { "aspern": { "type": "http", "url": "https://aspern.org/mcp" } } }

Raw JSON-RPC:

curl -s https://aspern.org/mcp \

-H 'content-type: application/json' \ -H 'accept: application/json, text/event-stream' \ -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Examples

In examples/, each one runnable as is:

• counterparty-check.sh 0xADDRESS — the free counterparty record over REST
• mcp-call.sh ' ' — any MCP tool over plain JSON-RPC
• x402-price-discovery.sh 0xADDRESS — a paid endpoint's 402 answer, which states its price

Tools

The full list, with each tool's description and input schema as the server returns it, is in docs/tools.md (generated from tools/list, dated; refresh with node scripts/gen-docs.mjs). The agent card is mirrored in docs/agent-card.json. The server is the source of truth: if the two differ, the server is right and this file is stale.

Pricing

Free tools need no key and no payment. Paid calls are priced per call and paid over x402 (USDC); the endpoint answers 402 Payment Required with the price and how to pay it, so an agent can discover the price before it pays. Current prices: https://aspern.org/data and docs/pricing.md (generated).

What ASPERN does not do

• It never holds, moves or signs for anyone's funds.
• It does not rank, rate or recommend. A reading describes the record behind a figure; it is not a credit rating and not investment advice.
• It does not accept paid placement.

Registry entry

server.json is the entry published to the official MCP registry as org.aspern/aspern.

Contact and security

• Corrections and questions: see https://aspern.org/support
• Security reports: SECURITY.md and https://aspern.org/.well-known/security.txt

Licence

The documentation in this repository is licensed under CC BY 4.0. The ASPERN service, its data and its source code are not covered by this licence; see https://aspern.org/terms.