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nws-weather-mcp-server

by io.github.cyanheads
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Nws Get Zone Forecast

nws_get_zone_forecast
Read-only

Get the text forecast for a public NWS forecast zone. Returns named forecast periods (e.g., "Today", "Tonight", "Monday") with detailed narrative text — the human-readable, zone-level forecast written by local forecasters. Completes the alert-to-forecast chain: nws_search_alerts returns each affected zone in "affectedZones" as a code plus a type, and nws_find_stations returns codes in the "forecastZone" column. Only affectedZones entries with type "forecast" work here; entries typed "county" or "fire" have no text forecast upstream and will not resolve. Zone codes follow the pattern XXZ### (e.g., "WAZ315" for Western Washington lowlands).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
zone_idYesNWS public forecast zone code (e.g., "WAZ315" for the Western Washington lowlands including Seattle). Returned as "forecastZone" by nws_get_forecast and nws_find_stations, or as the "code" of an "affectedZones" entry with type "forecast" in nws_search_alerts. Format: two-letter state + "Z" + three-digit number.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
errorNoPresent when the call failed. Absent on success.
zoneIdNoZone ID as provided (e.g., "WAZ315").
periodsNoForecast periods in chronological order, typically covering 7 days.
updatedNoWhen the zone forecast was last updated (ISO 8601 with timezone offset).
periodCountNoNumber of forecast periods returned.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedOutput schema / properties / error / properties / data / properties / reason / description
      Previous value: -"Machine-readable failure mode. Declared by this tool: `zone_not_found`: Zone code is not a valid public forecast zone or has no forecast available Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `zone_not_found`: Zone code is not a valid public forecast zone or has no forecast available. Other values are possible when a failure originates below the handler."
  2. Changed6 schema fields changed
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
    • addedInput schema / additionalProperties
      Added value: +false
    • changedOutput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
    • addedOutput schema / anyOf
      Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "zoneId",
+      "updated",
+      "periods",
+      "periodCount"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]
    • addedOutput schema / properties / error
      Added value: +{
+  "additionalProperties": {},
+  "description": "Present when the call failed. Absent on success.",
+  "properties": {
+    "code": {
+      "description": "JSON-RPC error code for this failure.",
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "data": {
+      "additionalProperties": {},
+      "properties": {
+        "reason": {
+          "description": "Machine-readable failure mode. Declared by this tool: `zone_not_found`: Zone code is not a valid public forecast zone or has no forecast available Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "zone_not_found"
+          ],
+          "type": "string"
+        },
+        "recovery": {
+          "additionalProperties": {},
+          "description": "Actionable next step for the caller.",
+          "properties": {
+            "hint": {
+              "type": "string"
+            }
+          },
+          "required": [
+            "hint"
+          ],
+          "type": "object"
+        },
+        "retryable": {
+          "description": "Whether retrying may succeed.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "message": {
+      "description": "Human-readable description of what went wrong.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "code",
+    "message"
+  ],
+  "type": "object"
+}
    • removedOutput schema / required
      Removed value: -[
-  "zoneId",
-  "updated",
-  "periods",
-  "periodCount"
-]
  3. Changed1 schema field changed
    • changedInput schema / properties / zone_id / description
      Previous value: -"NWS public forecast zone code (e.g., \"WAZ315\" for the Western Washington lowlands including Seattle). Returned as \"forecastZone\" by nws_get_forecast and nws_find_stations, or in \"affectedZones\" by nws_search_alerts. Format: two-letter state + \"Z\" + three-digit number."New value: +"NWS public forecast zone code (e.g., \"WAZ315\" for the Western Washington lowlands including Seattle). Returned as \"forecastZone\" by nws_get_forecast and nws_find_stations, or as the \"code\" of an \"affectedZones\" entry with type \"forecast\" in nws_search_alerts. Format: two-letter state + \"Z\" + three-digit number."
  4. Added

TDQS

A3.8/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, so the read-only nature is covered. The description adds valuable behavioral context about zone type restrictions (only 'forecast' type resolves) and the zone code pattern (XXZ###), which goes beyond the annotation. It does not discuss permissions or rate limits, but those are not critical here.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is moderately long but every sentence earns its place: it leads with the core action, then explains the workflow context, zone type restrictions, and code format. It is well-structured and front-loaded with the main purpose, with no redundant filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present (indicated by 'Has output schema: true'), the description need not explain return structure. It covers the tool's role in the forecast chain, the acceptable zone types, and the code pattern, making it sufficiently complete for an agent to call it correctly. Minor omissions like error handling are not critical.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3. The description adds significant meaning beyond the schema by explaining where zone_id originates (from nws_search_alerts or nws_find_stations) and clarifying the format with examples, which helps the agent understand the parameter's provenance and validation.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool retrieves text forecasts for NWS zones and returns named forecast periods with narrative text. It distinguishes from siblings by mentioning the alert-to-forecast chain and the zone code sources, though it does not explicitly compare with nws_get_forecast or nws_get_observations.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It provides explicit usage context: 'Completes the alert-to-forecast chain' and explains that only affectedZones with type 'forecast' work, while county or fire types will not resolve. This gives both when-to-use and when-not-to-use guidance, though it does not name alternative tools directly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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