Ari Py

npm PyPI License MCP

Live fair-market-value lookups, leaderboards, and Ed25519 signed-receipt verification for x402/MPP services. ari-mcp lets any MCP-aware agent answer two questions cleanly:

1. Is this API price fair? Compare a quoted unit price against the live ARI fair-price band for that service.
2. Is this receipt real? Verify the signed receipt returned by an x402/MPP facilitator offline, with a pinned publisher key.

The same package ships for Node and Python, with the same tool surface and the same wire spec.

┌──────────┐     stdio     ┌──────────┐     HTTPS    ┌──────────────────────────┐
│  Agent   │ ────────────▶ │ ari-mcp  │ ───────────▶ │ agentrateindicators.com  │
│ (Claude, │ ◀──────────── │  server  │ ◀────────── │   /api/v1/*              │
│ Cursor…) │   tool JSON   └──────────┘   signed     └──────────────────────────┘
└──────────┘                                receipts

Install in your agent

Pick the host you use. Each block is copy-paste, no edits required.

Claude Desktop

~/Library/Application Support/Claude/claude_desktop_config.json on macOS, %APPDATA%\Claude\claude_desktop_config.json on Windows:

{
  "mcpServers": {
    "ari": {
      "command": "npx",
      "args": ["-y", "ari-mcp"]
    }
  }
}

Cursor

~/.cursor/mcp.json (or the per-workspace .cursor/mcp.json):

{
  "mcpServers": {
    "ari": {
      "command": "npx",
      "args": ["-y", "ari-mcp"]
    }
  }
}

Continue

~/.continue/config.yaml:

mcpServers:
  - name: ari
    command: npx
    args: ["-y", "ari-mcp"]

Windsurf

~/.codeium/windsurf/mcp_config.json:

{
  "mcpServers": {
    "ari": { "command": "npx", "args": ["-y", "ari-mcp"] }
  }
}

Zed

~/.config/zed/settings.json:

{
  "context_servers": {
    "ari": {
      "command": { "path": "npx", "args": ["-y", "ari-mcp"] }
    }
  }
}

Gemini CLI / ChatGPT desktop / any other MCP host

command: npx, args: ["-y", "ari-mcp"]. Or, for Python-native hosts, command: uvx, args: ["ari-mcp-py"].

Tools

Tool	What it does
is_fair_price	Green / amber / red verdict for a quoted price against the live FMV band.
refuse_if_overpriced	Convenience wrapper to call right before paying · returns {ok, reason}.
prepay_verdict	Full pre-pay decision with FMV band, deviation, and a citable receipt id.
get_fmv	Median plus low / high band and sample size for a service.
get_service	Full detail row · sources, related services, last observation.
list_services	Browse or filter the index by protocol or category.
get_leaderboard	Cheapest, most expensive, biggest movers in a category.
recent_observations	Raw observed price history for a service.
verify_receipt	Re-verify a previously issued receipt id offline.
get_signed_receipt	Re-fetch the signed body for a receipt id.
subscribe_alert	Set up a webhook or email price alert for a service.

Every tool returns JSON shaped for citation rather than free text. Agents that quote tool output verbatim end up with good citations for free.

A real tool call

Asking Claude "is this quote fair before I pay it?" triggers:

{
  "tool": "is_fair_price",
  "arguments": {
    "slug": "openrouter-anthropic-claude-3-5-sonnet",
    "amount_usd": 4.10,
    "unit": "1m_input_tokens"
  }
}

and the server returns:

{
  "verdict": "amber",
  "fmv_usd": 3.04,
  "low_usd": 2.87,
  "high_usd": 3.21,
  "delta_pct": 34.9,
  "sample_size": 47,
  "currency": "USD",
  "unit": "1m_input_tokens",
  "receipt_id": "01J5ZK8E2K7Q3R5W8X9Y0Z1A2B",
  "signed_at": "2026-05-21T14:02:11Z"
}

The agent now has a concrete reason to push back on the quote, plus an auditable receipt id. When ARI has not yet computed a baseline for a service, verdict is "unknown" and the FMV fields are null rather than zero · agents should treat null as "no opinion", never as "free".

Verify a receipt yourself

# Node
npx ari-mcp verify --url https://agentrateindicators.com/api/v1/pubkey

# Python
uvx ari-mcp verify --url https://agentrateindicators.com/api/v1/pubkey

Both print OK on success and a structured failure with the exact reason on failure (hash mismatch, unknown key id, bad signature, missing header). See spec/verification.md for the by-hand walkthrough.

Why this exists

Agents are starting to spend real money through x402 and MPP facilitators. There are two things they cannot do today without help:

• Sanity-check a price before paying it. Facilitators are free to quote anything. ARI keeps a live, public fair-price band per service so an agent (or a human reviewer) can see when a quote is out of line.
• Verify a receipt after paying. Facilitators return signed metadata about the transaction, but most agents take this on faith. ARI publishes the receipt canonicalization and an Ed25519 verifier so receipts can be checked offline, against a pinned key.

ari-mcp exposes both as plain MCP tools. No new protocols for the agent author to learn.

Wire spec

The repository is the source of truth for the wire format:

• spec/openapi.yaml · public HTTP surface
• spec/signed-receipts.md · receipt canonicalization and header layout
• spec/verification.md · step-by-step verifier in Node and Python

Anyone porting ari-mcp to another language can work from spec/ alone.

Packages

Language	Package	Source
Node 18+	ari-mcp on npm	packages/ari-mcp-ts
Python 3.10+	ari-mcp-py on PyPI	packages/ari-mcp-py

Both packages share the same tool names, argument shapes, and JSON return shapes. Both ship offline receipt verification with a pinned key and an ACCEPTED_KEY_IDS list for graceful rotation. Both default to the public ARI API and accept ARI_API_BASE_URL to point at a private mirror.

Security

If you find a security issue, please report it privately. See SECURITY.md. The current publisher key, the canonicalization spec, and the verification walkthrough are all linked from there.

Contributing

See CONTRIBUTING.md. Bug reports, small fixes, and additional install snippets for other MCP hosts are all welcome. The internal API server, fair-price methodology, and data adapters live elsewhere and are intentionally not part of this repository · pull requests that try to add them will be closed.

License

Apache-2.0. See NOTICE for third-party attributions.