# grounded-evidence-step

`station__grounded__grounded-evidence-step` · external (needs EXECUTION_BACKEND_URL configured) · domain `grounded` · pv-relevance `non-pv`

Add a step to an existing evidence chain (strengthen or weaken).

> **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

- `chain_id` *string* (required) — Chain ID (from grounded_evidence_new)
- `description` *string* (required) — Description of this evidence step
- `direction` *string* (required) — Direction: "strengthen" or "weaken"
- `factor` *number* (required) — Factor magnitude in [0.0, 1.0]

## Example call

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

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "station__grounded__grounded-evidence-step",
    "arguments": {
      "chain_id": "",
      "description": "",
      "direction": "",
      "factor": 0
    }
  }
}
```

## Related

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