PayStage Preflight

xyz.paystagePublished by paystage.xyzv0.1.0Updated Oct 30, 2026

Evaluate x402 PaymentRequired against a local spending policy before an agent pays

The publisher's own server: Preflight

VerifiedSTDIODesktop onlyFinance Security & Monitoring

Server details

Identifier: xyz.paystage/preflight
Transport: STDIO
Runtime: Desktop only
Trust: Verified
Published: Oct 30, 2026

Security note

MCP servers receive tool arguments from a conversation and may perform external actions. Review what a server can do before you enable it, and give it only the access it needs.

The registry verified that this server's namespace belongs to paystage.xyz. It runs from a package rather than a hosted endpoint, so there is no endpoint to match against that domain.

SourceWeft's checks cover whether the listing is complete and the endpoint answered; they do not review the server's code or what its tools do.

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Overview

AI-generated overview

Local stdio MCP server that checks an x402 PaymentRequired payload against a JSON spending policy and returns pay, review or do_not_pay before an agent pays.

What you can do: Evaluate a single x402 PaymentRequired payload against a local spending policy before payment.
Return one of three verdicts: pay, review (above a human threshold) or do_not_pay for policy violations.
Apply rules for allowed networks, assets, payee addresses, per-call and per-session amount caps, human-review thresholds and timeouts.
Work deterministically from a local policy file, with no network calls or secrets needed to decide.
When to use it: Useful when an agent can make x402 payments and you want a deterministic, local gate that blocks or escalates payments outside your spending rules before any money moves.
Requirements: Runs locally over stdio, typically via npx with Node.js, or added to an MCP client config such as Claude Desktop or Cursor. Requires a policy JSON file whose absolute path is set in the PAYSTAGE_POLICY_PATH environment variable. Desktop-only; no authentication declared.

Before you install

The server only returns a verdict; it does not pay, so enforcement depends on your agent or client honoring do_not_pay and review. A missing or misconfigured policy file can weaken the gate, and the default verdict in the example policy is review. Amounts are in USDC and network and payee allowlists must be set correctly.

Installation

In SourceWeft

Open PayStage Preflight in the dashboard and add it to a workspace.
Enable the server for the chats that should use its tools.

Desktop only via STDIO. STDIO servers start a local process, so they need the SourceWeft desktop host.

Other MCP clients

Follow the launch instructions in the repository.

README

@paystage/preflight

Evaluate an x402 PaymentRequired against a local spending policy before your agent pays. Returns one of three verdicts: pay, review, or do_not_pay.

Local-first — policy lives in a JSON file on your machine. No secrets, no network calls to decide.
MCP-native — runs as a stdio MCP server so Claude Desktop, Cursor, and any MCP client can call it as a tool.
Deterministic — same input + same policy ⇒ same verdict.

Install

Run directly with npx (no global install):

Or add it to your MCP client config.

Claude Desktop

Add to claude_desktop_config.json:

json

{  "mcpServers": {    "paystage-preflight": {      "command": "npx",      "args": ["-y", "@paystage/preflight"],      "env": {        "PAYSTAGE_POLICY_PATH": "/absolute/path/to/policy.json"      }    }  }}

{  "mcpServers": {    "paystage-preflight": {      "command": "npx",      "args": ["-y", "@paystage/preflight"],      "env": {        "PAYSTAGE_POLICY_PATH": "/absolute/path/to/policy.json"      }    }  }}

Cursor

Add to .cursor/mcp.json:

json

{  "mcpServers": {    "paystage-preflight": {      "command": "npx",      "args": ["-y", "@paystage/preflight"],      "env": {        "PAYSTAGE_POLICY_PATH": "/absolute/path/to/policy.json"      }    }  }}

{  "mcpServers": {    "paystage-preflight": {      "command": "npx",      "args": ["-y", "@paystage/preflight"],      "env": {        "PAYSTAGE_POLICY_PATH": "/absolute/path/to/policy.json"      }    }  }}

Example `policy.json`

json

{  "version": 1,  "name": "standard",  "allowed_networks": ["eip155:8453", "eip155:84532"],  "allowed_assets": [    "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",    "0x036CbD53842c5426634e7929541eC2318f3dCF7e"  ],  "allowed_pay_to": ["0x209693Bc6afc0C5328bA36FaF03C514EF312287C"],  "max_amount_per_call": "1.00",  "max_amount_per_session": "10.00",  "require_human_above": "0.50",  "max_timeout_seconds": 300,  "default_verdict": "review"}

{  "version": 1,  "name": "standard",  "allowed_networks": ["eip155:8453", "eip155:84532"],  "allowed_assets": [    "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",    "0x036CbD53842c5426634e7929541eC2318f3dCF7e"  ],  "allowed_pay_to": ["0x209693Bc6afc0C5328bA36FaF03C514EF312287C"],  "max_amount_per_call": "1.00",  "max_amount_per_session": "10.00",  "require_human_above": "0.50",  "max_timeout_seconds": 300,  "default_verdict": "review"}

Amounts are human-readable USDC (e.g. "0.50" = 0.50 USDC). Networks use CAIP-2 identifiers.

Verdicts

Verdict	Meaning
`pay`	Within policy — safe to proceed automatically.
`review`	Allowed but above a human threshold — ask a human before paying.
`do_not_pay`	Violates policy (network, asset, payTo, amount, timeout, or malformed).

Tools

evaluate_mcp_payment

Evaluate an x402 PaymentRequired payload against a PayStage spending policy before paying

Parameterspolicypolicy_pathpayment_required

Version history

v0.1.0LatestOct 30, 2026

Score

90% of the applicable checks met

How complete this listing is, computed from the registry entry, the endpoint and public sources. Not a rating of the server and not a statement that it is safe or working today: reachability is a dated check, and no installs or reviews go into the score.

Reached in the last 30 days25 pts
Auth declared10 pts
Declare the credential headers in the registry entry, or keep the endpoint answering the probe so its auth can be classified.
Tools listedRequired15 pts
DescriptionRequired15 pts
Logo10 pts
Documentation15 pts
License10 pts