lookup_uk_postcodeAddresses for a UK postcode (rate limited upstream). Returns matching addresses or suggestions when the postcode is incomplete.
| Name | Required | Description | Default |
|---|---|---|---|
| postcode | Yes | UK postcode, e.g. NW2 7JW. |
| Name | Required | Description | Default |
|---|---|---|---|
| status | Yes | ||
| addresses | Yes | ||
| suggestions | Yes | Possible postcodes when the one given is incomplete. |
Changes observed during successful MCP inspections.
Output schema / (root)Previous value: -nullNew value: +{
+ "$schema": "http://json-schema.org/draft-07/schema#",
+ "additionalProperties": false,
+ "properties": {
+ "addresses": {
+ "items": {
+ "additionalProperties": false,
+ "properties": {
+ "county": {
+ "anyOf": [
+ {
+ "type": "string"
+ },
+ {
+ "type": "null"
+ }
+ ]
+ },
+ "label": {
+ "type": "string"
+ },
+ "line_1": {
+ "anyOf": [
+ {
+ "type": "string"
+ },
+ {
+ "type": "null"
+ }
+ ]
+ },
+ "line_2": {
+ "anyOf": [
+ {
+ "type": "string"
+ },
+ {
+ "type": "null"
+ }
+ ]
+ },
+ "post_town": {
+ "anyOf": [
+ {
+ "type": "string"
+ },
+ {
+ "type": "null"
+ }
+ ]
+ },
+ "postcode": {
+ "anyOf": [
+ {
+ "type": "string"
+ },
+ {
+ "type": "null"
+ }
+ ]
+ }
+ },
+ "required": [
+ "label",
+ "line_1",
+ "line_2",
+ "post_town",
+ "county",
+ "postcode"
+ ],
+ "type": "object"
+ },
+ "type": "array"
+ },
+ "status": {
+ "type": "string"
+ },
+ "suggestions": {
+ "description": "Possible postcodes when the one given is incomplete.",
+ "items": {
+ "type": "string"
+ },
+ "type": "array"
+ }
+ },
+ "required": [
+ "status",
+ "addresses",
+ "suggestions"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool as read-only, and the description adds meaningful behavior beyond that: upstream rate limiting and graceful fallback to suggestions for incomplete postcodes. No contradiction with the annotations exists.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two short sentences with no filler. The core behavior and an important caveat (rate limiting) are front-loaded, and the fallback behavior follows naturally.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a single-parameter, read-only lookup with an output schema, the description is sufficiently complete: it covers the core behavior, the rate-limit caveat, and the incomplete-postcode fallback. No essential invocation detail is missing.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% and the single parameter already includes an example. The description adds value by indicating that incomplete postcodes are accepted and produce suggestions, which is not stated in the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the operation ('Returns matching addresses or suggestions for a UK postcode') and identifies the resource. It is immediately distinguishable from the product/cart/order sibling tools, none of which perform postcode address lookup.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Usage is implied rather than explicit: an agent can infer this tool is for UK postcode address lookups, but the description does not name alternatives or state when-not-to-use it. The note about incomplete postcodes gives some input-handling guidance but no comparative routing.
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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