UK Postcode Intel

Postcode Lookup

postcode_lookup

Look up a UK postcode: coordinates, local authority, ward, constituency, region, LSOA/MSOA codes and country (source: ONS via postcodes.io).

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "postcode": "<postcode>"
    },
    "name": "postcode_lookup"
  }
}

Input Schema

Name	Required	Description	Default
`postcode`	Yes	Any UK postcode, e.g. "SW1A 1AA".

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 14, 2026

TDQS

A4/5.0

Behavior3/5

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

No annotations are supplied, so the description must carry the behavioral burden. It helpfully discloses the data source (ONS via postcodes.io) and that coverage is UK-only, which implies a read-only reference lookup, but it does not say what happens on an invalid or partial postcode, whether lookups are rate-limited, or how stale the data is.

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?

One sentence, front-loaded with the verb and resource, with the returned fields and source packed in afterward. Nothing is wasted and nothing important is buried.

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?

An output schema exists, so enumerating the returned fields is somewhat redundant, but the source attribution and UK-only scope are genuinely useful additions for a one-parameter lookup. The only meaningful gap is error behavior for malformed postcodes.

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% and the single parameter already carries an example, so the baseline is 3. The description adds real constraint beyond the schema by scoping the input to UK postcodes specifically, signalling it will reject non-UK input, though it adds no format or normalization detail.

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?

States a specific verb and resource ("Look up a UK postcode") and enumerates exactly what comes back: coordinates, local authority, ward, constituency, region, LSOA/MSOA codes and country. It is clearly a single-postcode geocoding/reference lookup, distinct from siblings such as area_report or crime_summary.

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

Usage Guidelines3/5

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

The description implies when to use it (resolving a UK postcode into official geography codes), but gives no explicit when-to-use rule, no prerequisite context, and no pointer to the sibling that would take a postcode for broader analysis. Usage is inferable rather than stated.

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

All UK Postcode Intel tools Inspect

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