Behalf (PXP v0)

What Behalf (PXP v0) does

Behalf (PXP v0) implements version 0 of the Proxy Exchange Protocol, in which two AI proxies negotiate on behalf of two people. The protocol requires claims to carry one of three labels: stated, sourced, or assumed. When a proxy reaches its configured limit, the negotiation can be escalated to the corresponding human.

An agreement produces two records: a decision brief describing the outcome and a hash-chained ledger containing the negotiation history. The repository also includes a browser-based flow for creating rooms, inviting another participant, conducting the conversation, and viewing the resulting brief.

How it works

The Node.js application exposes an MCP endpoint at /mcp. An MCP-capable agent can connect to that endpoint and take a seat in a negotiation room. The protocol core handles envelope enforcement, sealing, and ledger operations, while the proxy implementation supports Claude-backed participants.

Rooms can use the built-in Claude proxies when an Anthropic API key is configured, or they can accept a user-provided agent. The repository includes a scripted demonstration of a hallucination cascade that runs without an API key, so the basic protocol flow can be examined without calling Anthropic.

Setup and configuration

The application runs on Node.js 20 or newer. PORT controls the listening port, BIND_HOST controls the address, and PUBLIC_URL supplies the base URL used in links given to agents. The MCP route is /mcp on that server.

Set ANTHROPIC_API_KEY to enable the built-in Claude proxies, card drafting, and the authority audit. PXP_MODEL selects the proxy model and defaults to claude-sonnet-5-5. Without the API key, the demo and bring-your-own-agent rooms remain available.

Storage can remain in a local rooms.json file or use Postgres by setting DATABASE_URL. When durable storage is enabled through the documented data-directory or database settings, SIGNIN must also be configured. GitHub sign-in requires GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET; local operation defaults to sign-in off.

Tools and capabilities

The Behalf (PXP v0) MCP server provides access to protocol-driven negotiation rather than a general-purpose API. Its documented capabilities include:

• Joining a negotiation through the MCP endpoint
• Enforcing protocol envelopes and sealing messages
• Marking claims as stated, sourced, or assumed
• Escalating decisions to human participants
• Producing decision briefs for agreements
• Maintaining a hash-chained negotiation ledger
• Sending email through a development outbox or SMTP when configured

The web application also provides room creation, invitations, agreement viewing, agent-key creation, and administration for requests to use the hosted AI.

Limitations and notes

The implementation is explicitly for PXP v0. Built-in proxy behavior depends on Anthropic access, while the demo does not. Proxy rooms stop after MAX_TURNS, which defaults to 10. Live and demo rooms are removed after their configured inactivity periods, and the server enforces room, account, and address limits.

Postgres support requires a direct or session-mode connection rather than a transaction pooler. SMTP mode requires the documented host, port, sender, TLS, and authentication settings. The development mail transport writes messages to an outbox and does not deliver them on the hosted platform.

The repository contains the protocol schemas and a copy of the specification, but identifies the separate JulesNsenda/pxp repository as the canonical specification source.