capabilities

Get the US weather forecast for coordinates (NWS)

weather_us_forecast

Read-onlyIdempotent

Official National Weather Service forecast for any US coordinate - six 12-hour day/night periods by default, or hourly - each with temperature in C and F, precipitation probability, a wind speed range in km/h, wind direction and a short forecast, plus the NWS issue time so an agent can judge its age. Use when: What is the weather forecast for these US coordinates? Not for: You need the latest observed conditions and their age - use weather.us.observation. Related: weather_us_observation; weather_us_alerts. Price: USD 0.003/call (x402), 0.002 (account key).

Input Schema

TableJSON Schema

Name	Required	Description	Default
`lat`	Yes	Latitude in decimal degrees (WGS84). Rounded to 4 decimal places before the National Weather Service lookup.
`lon`	Yes	Longitude in decimal degrees (WGS84). Rounded to 4 decimal places before the National Weather Service lookup.
`hours`	No	Number of hourly periods to return, soonest first. Applies when hourly is true; use period_limit for day/night forecasts.
`detail`	No	compact (default) returns the fields an agent acts on. full adds the NWS narrative (detailed_forecast), the icon URL, the trend note and, for hourly periods, dewpoint_c and humidity_pct.	compact
`hourly`	No	Return hourly periods instead of the default 12-hour day/night periods. Hourly periods have no name and, at detail=full, carry dewpoint and humidity.
`period_limit`	No	Maximum number of 12-hour day/night periods to return, soonest first. Applies when hourly is false; use hours for hourly forecasts. NWS issues 14 periods (7 days); the default of 6 is three days. Named period_limit, not periods, because periods is the returned series.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`data`	Yes	Capability output; full JSON Schema at https://api.eckari.com/v1/capabilities/weather.us.forecast
`meta`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedAug 18, 2026

changedInput schema / properties / hours / description

Previous value: -"Number of hourly periods to return, soonest first. Applies when hourly is true; use periods for day/night forecasts."New value: +"Number of hourly periods to return, soonest first. Applies when hourly is true; use period_limit for day/night forecasts."

addedInput schema / properties / period_limit

Added value: +{
+  "default": 6,
+  "description": "Maximum number of 12-hour day/night periods to return, soonest first. Applies when hourly is false; use hours for hourly forecasts. NWS issues 14 periods (7 days); the default of 6 is three days. Named period_limit, not periods, because periods is the returned series.",
+  "maximum": 14,
+  "minimum": 1,
+  "type": "integer"
+}

removedInput schema / properties / periods

Removed value: -{
-  "default": 6,
-  "description": "Number of 12-hour day/night periods to return, soonest first. Applies when hourly is false; use hours for hourly forecasts. NWS issues 14 periods (7 days); the default of 6 is three days.",
-  "maximum": 14,
-  "minimum": 1,
-  "type": "integer"
-}

Changed12 schema fields changedAug 18, 2026

addedInput schema / properties / detail

Added value: +{
+  "default": "compact",
+  "description": "compact (default) returns the fields an agent acts on. full adds the NWS narrative (detailed_forecast), the icon URL, the trend note and, for hourly periods, dewpoint_c and humidity_pct.",
+  "enum": [
+    "compact",
+    "full"
+  ],
+  "type": "string"
+}

addedInput schema / properties / hourly / default
```
Added value: +false
```

changedInput schema / properties / hourly / description

Previous value: -"Return hourly periods instead of the default 12-hour day/night periods."New value: +"Return hourly periods instead of the default 12-hour day/night periods. Hourly periods have no name and, at detail=full, carry dewpoint and humidity."

addedInput schema / properties / hours

Added value: +{
+  "default": 24,
+  "description": "Number of hourly periods to return, soonest first. Applies when hourly is true; use periods for day/night forecasts.",
+  "maximum": 48,
+  "minimum": 1,
+  "type": "integer"
+}

addedInput schema / properties / periods

Added value: +{
+  "default": 6,
+  "description": "Number of 12-hour day/night periods to return, soonest first. Applies when hourly is false; use hours for hourly forecasts. NWS issues 14 periods (7 days); the default of 6 is three days.",
+  "maximum": 14,
+  "minimum": 1,
+  "type": "integer"
+}

removedOutput schema / properties / data / additionalProperties
```
Removed value: -false
```

addedOutput schema / properties / data / description

Added value: +"Capability output; full JSON Schema at https://api.eckari.com/v1/capabilities/weather.us.forecast"

removedOutput schema / properties / data / properties

Removed value: -{
-  "generated_at": {
-    "description": "Time NWS generated this response from the forecast grid.",
-    "type": [
-      "string",
-      "null"
-    ]
-  },
-  "location": {
-    "additionalProperties": false,
-    "properties": {
-      "city": {
-        "description": "Nearest named place reported by NWS for the point; null when NWS omits it.",
-        "type": [
-          "string",
-          "null"
-        ]
-      },
-      "grid": {
-        "additionalProperties": false,
-        "properties": {
-          "office": {
-            "description": "NWS weather forecast office identifier (for example LWX) that issued this forecast.",
-            "type": "string"
-          },
-          "x": {
-            "description": "Forecast grid X coordinate for the office.",
-            "type": "integer"
-          },
-          "y": {
-            "description": "Forecast grid Y coordinate for the office.",
-            "type": "integer"
-          }
-        },
-        "required": [
-          "office",
-          "x",
-          "y"
-        ],
-        "type": "object"
-      },
-      "lat": {
-        "description": "Latitude actually queried (rounded to 4 decimal places).",
-        "type": "number"
-      },
-      "lon": {
-        "description": "Longitude actually queried (rounded to 4 decimal places).",
-        "type": "number"
-      },
-      "state": {
-        "description": "Two-letter US state or territory code.",
-        "type": [
-          "string",
-          "null"
-        ]
-      },
-      "timezone": {
-        "description": "IANA timezone of the point as reported by NWS.",
-        "type": [
-          "string",
-          "null"
-        ]
-      }
-    },
-    "required": [
-      "lat",
-      "lon",
-      "grid",
-      "city",
-      "state",
-      "timezone"
-    ],
-    "type": "object"
-  },
-  "periods": {
-    "description": "Forecast periods in chronological order, as issued by the forecast office.",
-    "items": {
-      "additionalProperties": false,
-      "properties": {
-        "detailed_forecast": {
-          "description": "Detailed narrative issued by NWS; null for hourly periods.",
-          "type": [
-            "string",
-            "null"
-          ]
-        },
-        "dewpoint_c": {
-          "description": "Dewpoint in degrees Celsius (hourly periods only); rounded to 2 decimal places.",
-          "type": [
-            "number",
-            "null"
-          ]
-        },
-        "end": {
-          "description": "Period end (ISO 8601 with UTC offset).",
-          "type": "string"
-        },
-        "humidity_pct": {
-          "description": "Relative humidity as a percentage (hourly periods only); rounded to 2 decimal places.",
-          "type": [
-            "number",
-            "null"
-          ]
-        },
-        "icon": {
-          "description": "NWS icon URL for the period.",
-          "type": [
-            "string",
-            "null"
-          ]
-        },
-        "is_daytime": {
-          "description": "True when the National Weather Service marks the period as daytime, false when it marks it as night, null when the forecast omits the flag - null is not night.",
-          "type": [
-            "boolean",
-            "null"
-          ]
-        },
-        "name": {
-          "description": "Period label such as Tonight or Tuesday; null for hourly periods.",
-          "type": [
-            "string",
-            "null"
-          ]
-        },
-        "number": {
-          "description": "Sequence number of the period.",
-          "type": [
-            "integer",
-            "null"
-          ]
-        },
-        "precipitation_probability_pct": {
-          "description": "Probability of precipitation for the period as a percentage; null when not forecast.",
-          "type": [
-            "number",
-            "null"
-          ]
-        },
-        "short_forecast": {
-          "description": "Short forecast phrase issued by NWS.",
-          "type": [
-            "string",
-            "null"
-          ]
-        },
-        "start": {
-          "description": "Period start (ISO 8601 with UTC offset).",
-          "type": "string"
-        },
-        "temperature": {
-          "description": "Forecast temperature expressed in temperature_unit.",
-          "type": [
-            "number",
-            "null"
-          ]
-        },
-        "temperature_trend": {
-          "description": "NWS trend note such as rising or falling; usually null.",
-          "type": [
-            "string",
-            "null"
-          ]
-        },
-        "temperature_unit": {
-          "description": "Unit letter as issued by NWS - F for Fahrenheit or C for Celsius. US forecasts are issued in F. Null when the forecast omits the unit or issues one this contract does not recognise; the temperature is then a number with no stated unit, never assumed to be Fahrenheit.",
-          "type": [
-            "string",
-            "null"
-          ]
-        },
-        "wind_direction": {
-          "description": "Compass direction as issued by NWS (for example NW).",
-          "type": [
-            "string",
-            "null"
-          ]
-        },
-        "wind_speed": {
-          "description": "Wind speed exactly as issued by NWS - typically an mph range such as 2 to 7 mph.",
-          "type": [
-            "string",
-            "null"
-          ]
-        }
-      },
-      "required": [
-        "number",
-        "name",
-        "start",
-        "end",
-        "is_daytime",
-        "temperature",
-        "temperature_unit",
-        "short_forecast"
-      ],
-      "type": "object"
-    },
-    "type": "array"
-  },
-  "units": {
-    "description": "Unit system of the period values as issued by NWS - \"us\" means temperatures in Fahrenheit and wind as an mph text range.",
-    "type": "string"
-  },
-  "updated_at": {
-    "description": "Time the forecast product was issued by the forecast office (NWS updateTime). This is the true age of the forecast.",
-    "type": [
-      "string",
-      "null"
-    ]
-  },
-  "valid_from": {
-    "description": "Start of the validity interval of the underlying forecast grid.",
-    "type": [
-      "string",
-      "null"
-    ]
-  }
-}

removedOutput schema / properties / data / required

Removed value: -[
-  "location",
-  "updated_at",
-  "generated_at",
-  "valid_from",
-  "units",
-  "periods"
-]

addedOutput schema / properties / meta / properties / attribution_url
```
Added value: +{
+  "format": "uri",
+  "type": "string"
+}
```
addedOutput schema / properties / meta / properties / retrieved_at / format
```
Added value: +"date-time"
```

addedOutput schema / properties / meta / required

Added value: +[
+  "capability",
+  "version",
+  "retrieved_at",
+  "source",
+  "freshness",
+  "request_id"
+]

First observedAug 18, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is clear. The description adds value by noting the NWS issue time field (allowing agent to judge data freshness) and pricing (USD 0.003/call). No contradictions with annotations.

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 a single, dense paragraph that front-loads the core purpose before listing features, usage guidance, and pricing. It is efficient with no wasted words, though a slightly more structured format (e.g., bullet points) could improve scanning. Still, every sentence adds value.

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

Completeness5/5

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

Given 6 parameters (all well-described in schema), an existing output schema, rich annotations, and a full sibling list, the description covers all essential aspects: purpose, output fields, usage boundaries, pricing, and temporal detail (NWS issue time). There are no missing pieces for an agent to correctly invoke the tool.

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 coverage is 100% with detailed parameter descriptions. The description supplements by clarifying the default behavior ('six 12-hour day/night periods by default, or hourly') and explaining the relationship between hours and period_limit parameters. This helps an agent choose the correct combination without reading the schema alone.

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

Purpose5/5

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

The description clearly states 'Official National Weather Service forecast for any US coordinate' and enumerates the returned data (six 12-hour periods or hourly, with temperature, precipitation, wind, etc.). It distinguishes from sibling tools weather_us_observation and weather_us_alerts by specifying scope and content.

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

Usage Guidelines5/5

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

Explicitly provides use-case guidance: 'Use when: What is the weather forecast for these US coordinates? Not for: You need the latest observed conditions and their age - use weather.us.observation.' It also lists related tools ('Related: weather.us.observation; weather.us.alerts'), leaving no ambiguity about when to invoke this tool versus alternatives.

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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