# advance

`station__helix__advance` · external (needs EXECUTION_BACKEND_URL configured) · domain `helix` · pv-relevance `non-pv`

Advance one turn on the helix. Given current turn and state, compute what the next turn requires. The truth doesn't change between turns — the resolution does. Returns the gap between current and next altitude.

> **Note:** This tool routes through an external execution backend. If `EXECUTION_BACKEND_URL` is unset on the server, calls return JSON-RPC error `-32603 "Tool execution backend not configured"`. Tools with `backend: native` execute in-process and are always callable.

## Agent metadata

- `idempotent`: unknown
- `read_only`: unknown
- `expected_latency_ms`: unknown (not yet contract-tested)
- `cost_tokens_estimate`: unknown

## Input schema

- `current_turn` *integer* (required) — Current helix turn (0-3). Cannot advance past turn 4.
- `current_existence` *number* (required) — Current ∃ score [0,1]
- `current_boundary` *number* (required) — Current ∂ score [0,1]
- `current_state` *number* (required) — Current ς score [0,1]

## Example call

```json
POST /api/mcp
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "station__helix__advance",
    "arguments": {
      "current_turn": 0,
      "current_existence": 0,
      "current_boundary": 0,
      "current_state": 0
    }
  }
}
```

## Related

- [/tools](/tools) — all 3062 tools
- [/tools/helix__advance](/tools/helix__advance) — HTML page
- [/tools/helix__advance/json](/tools/helix__advance/json) — JSON form (agent-friendly)
- [/api/mcp](/api/mcp) — endpoint
- [/AGENTS.md](/AGENTS.md) — agent guide