The Paycux MCP server

Three tools, one development environment

The server is part of the release source and registers itself to clients as paycux-agent. Every tool call is scoped to the project and development environment the agent token was issued for; the server refuses data outside that scope rather than passing it through.

• paycux_get_contract

  Reads the public integration contract for the linked project: project and environment ids, the source revision it was built from, integration instructions, hosted auth, checkout and portal URLs and public configuration. Read-only; contains no secrets.

• paycux_start_verification

  Starts a verification run for the linked development environment and returns its reference: an id and a state.

• paycux_get_verification

  Reads one verification run by id. The state is PASS, OPEN, BLOCKED or UNMEASURED. It never accesses provider secrets.

How it authenticates

The server needs an agent token: short-lived, prefixed pcx_, bound to one project's development environment and limited to the capabilities it was issued with. It reads the token from an inherited protected pipe, never from an argument, an environment value or a file, and it redacts tokens from its own error output.

• PAYCUX_AGENT_TOKEN_FD names the inherited file descriptor carrying the token (default 3); a regular file on that descriptor is refused
• PAYCUX_API_URL is the control-plane API address, https://api.paycux.com; unset, it defaults to a local development server
• Capabilities are contract:read, verification:start and verification:read; a token without one of them cannot call the matching tool

1# The token arrives on an inherited pipe (fd 3), never as an argument.
2PAYCUX_API_URL=https://api.paycux.com PAYCUX_AGENT_TOKEN_FD=3 \
3  paycux-mcp 3<"$PAYCUX_AGENT_TOKEN_PIPE"

The companion CLI

The same release source ships paycux, a CLI that uses the same agent token, read from a protected stdin pipe. It links a project, pulls the contract to disk and starts a verification run; the MCP server exposes the same three operations as tools.

1paycux link --project <project uuid> --environment development <"$PAYCUX_AGENT_TOKEN_PIPE"
2paycux contract pull --output paycux.contract.json <"$PAYCUX_AGENT_TOKEN_PIPE"
3paycux verify start <"$PAYCUX_AGENT_TOKEN_PIPE"

The pulled contract is written with owner-only file permissions. Agent connections are development-only: linking any other environment is refused.

What this page is not about

This server is a client of the Paycux control plane. It is not an authorization server for MCP servers you build yourself: OAuth for your own MCP servers is the planned Agent Access product and is not available today.