A session

Last updated 29 August 2026

1. Turn on billing and mint a key

Open /app, sign in, turn usage billing on. Hexum will not serve MCP until that is on. There is no spend cap. Rates: Pricing.

2. Paste MCP into the agent

mcp.json
{
  "mcpServers": {
    "hexum": {
      "serverUrl": "https://hexum.dev/mcp",
      "headers": { "Authorization": "Bearer hexum_live_…" }
    }
  }
}

Hexum MCP install for Cursor · Hexum for Claude Code.

3. Put a contract in the repo

architecture.hexum
skill full

layer ui
  match src/ui/**
  match src/pages/**

layer services
  match src/services/**

layer data
  match src/data/**

rule no_ui_to_data
  from ui
  cannot use data
  severity high
  message UI must not import data access directly.
  hint Call services instead.

4. Ask for a change as usual

The agent should call hexum_shrink, hexum_expand if needed, hexum_splice, then hexum_check.

FAQ

How do I add Hexum to Cursor?

Turn on usage billing at /app, mint a hexum_live_ key, paste the mcpServers JSON into Cursor Settings → MCP or ~/.cursor/mcp.json, then reload. Details: /cursor.

Why did MCP return BILLING or AUTH?

AUTH means the key is missing, invalid, or revoked. BILLING (HTTP 403) means the key is valid but usage billing is off — or, on a team, Teams billing is off. Turn billing on at /app, then retry.

What is architecture.hexum?

A file in the repo. Layers group files. Rules say a layer cannot use another. hexum_check reads it. Also accepted: hexum.hexum, .hexum, or the first *.hexum in the root. Guide: /architecture-hexum.