# gribstream_get_expression_reference

NO AUTH / PUBLIC / READ-ONLY. Gets the GribStream expression language reference, including github.com/expr-lang/expr syntax guidance, alias rules, examples, and the full exported func.* math function list. This tool does not query weather values and cannot return forecast data.

Agent View of the PolicyLayer registry record for `gribstream_get_expression_reference`. HTML page: https://policylayer.com/tools/com-gribstream-mcp/gribstream-get-expression-reference

## Facts

- Tool: `gribstream_get_expression_reference`
- Server: GribStream MCP (`https://gribstream.com/mcp`) — https://policylayer.com/tools/com-gribstream-mcp.md
- Homepage: https://github.com/GribStream/gribstream-mcp
- Risk category: Read (Low risk)
- Registry record: grade F, identity unverified
- Server auth posture: open
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Allowed

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "gribstream_get_expression_reference",
    "arguments": {}
  }
}
```

## Why gribstream_get_expression_reference is rated Low

This tool retrieves static reference documentation (expression language syntax, function list, examples) with no side effects, no data modification, and no ability to access or return actual weather data. It is a pure read operation returning informational content.

From the tool's own definition: "Tool description explicitly states 'NO AUTH / PUBLIC / READ-ONLY' and 'Gets the GribStream expression language reference'. It 'does not query weather values and cannot return forecast data', confirming it only retrieves reference documentation."

## Use case

AI agents call gribstream_get_expression_reference to retrieve information from GribStream MCP without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.

## Recommended policy (PolicyLayer)

Verdict: **Allowed**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches GribStream MCP:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "gribstream_get_expression_reference": {}
  }
}
```

## Other tools on GribStream MCP (11)

- `gribstream_build_runs_request` — Execute — https://policylayer.com/tools/com-gribstream-mcp/gribstream-build-runs-request.md
- `gribstream_build_timeseries_request` — Execute — https://policylayer.com/tools/com-gribstream-mcp/gribstream-build-timeseries-request.md
- `gribstream_get_dataset` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-get-dataset.md
- `gribstream_get_parameter` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-get-parameter.md
- `gribstream_list_datasets` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-list-datasets.md
- `gribstream_list_parameters` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-list-parameters.md
- `gribstream_list_shared_parameters` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-list-shared-parameters.md
- `gribstream_query_runs` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-query-runs.md
- `gribstream_query_timeseries` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-query-timeseries.md
- `gribstream_resolve_shared_parameter` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-resolve-shared-parameter.md
- `gribstream_validate_request` — Read — https://policylayer.com/tools/com-gribstream-mcp/gribstream-validate-request.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=com-gribstream-mcp · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/com-gribstream-mcp