What3words

Words To Coords

words_to_coords

Read-onlyIdempotent

Convert a 3-word address ("filled.count.soap") to a lat/lon centre + 3m×3m bounding box.

Input Schema

Name	Required	Description	Default
`words`	Yes	Three-word address (dot-separated)

Output Schema

Name	Required	Description
`words`	Yes	The 3-word address input
`country`	Yes	Country name containing the address
`map_url`	Yes	URL to view the address on what3words map
`latitude`	Yes	Latitude of the 3m×3m square center
`longitude`	Yes	Longitude of the 3m×3m square center
`square_ne`	Yes	Northeast corner of bounding box
`square_sw`	Yes	Southwest corner of bounding box
`nearest_place`	Yes	Nearest place name to the address

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedMay 22, 2026

addedInput schema / examples

Added value: +[
+  {
+    "words": "filled.count.soap"
+  },
+  {
+    "words": "index.home.raft"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "country": {
+      "description": "Country name containing the address",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "latitude": {
+      "description": "Latitude of the 3m×3m square center",
+      "type": [
+        "number",
+        "null"
+      ]
+    },
+    "longitude": {
+      "description": "Longitude of the 3m×3m square center",
+      "type": [
+        "number",
+        "null"
+      ]
+    },
+    "map_url": {
+      "description": "URL to view the address on what3words map",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "nearest_place": {
+      "description": "Nearest place name to the address",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "square_ne": {
+      "description": "Northeast corner of bounding box",
+      "properties": {
+        "lat": {
+          "description": "Northeast corner latitude",
+          "type": "number"
+        },
+        "lng": {
+          "description": "Northeast corner longitude",
+          "type": "number"
+        }
+      },
+      "type": [
+        "object",
+        "null"
+      ]
+    },
+    "square_sw": {
+      "description": "Southwest corner of bounding box",
+      "properties": {
+        "lat": {
+          "description": "Southwest corner latitude",
+          "type": "number"
+        },
+        "lng": {
+          "description": "Southwest corner longitude",
+          "type": "number"
+        }
+      },
+      "type": [
+        "object",
+        "null"
+      ]
+    },
+    "words": {
+      "description": "The 3-word address input",
+      "type": "string"
+    }
+  },
+  "required": [
+    "words",
+    "latitude",
+    "longitude",
+    "square_sw",
+    "square_ne",
+    "country",
+    "nearest_place",
+    "map_url"
+  ],
+  "type": "object"
+}

First observedMay 13, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already declare the tool safe, idempotent, and non-destructive. The description adds value by specifying the output shape (center + 3m×3m bounding box). It does not disclose potential errors or precision, but for a simple read operation, this is sufficient.

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

Conciseness5/5

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

A single, front-loaded sentence with an example. Every word is necessary, no filler. Excellent conciseness.

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 the tool's simplicity, rich annotations, full schema coverage, and presence of an output schema, the description provides all necessary context for correct invocation and understanding of the result.

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

Parameters3/5

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

Schema coverage is 100% and the schema already includes an example. The description's example is redundant. No additional meaning is provided for the 'words' parameter beyond what the schema offers, so it meets the baseline of 3.

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 uses a specific verb ('Convert') and resource ('3-word address'), clearly distinguishing this from its sibling 'coords_to_words' which does the reverse. The example and output details ('lat/lon centre + 3m×3m bounding box') solidify the purpose.

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?

The description implies usage by stating the conversion direction, but does not explicitly mention when not to use or point to the sibling for the reverse. However, the context of a straightforward conversion makes the usage clear, and the sibling list provides the alternative.

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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