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by io.github.simonmak-ascent
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companies_house_search

Read-onlyIdempotent

Search the UK Companies House register by name (requires COMPANIES_HOUSE_API_KEY). Returns company number, status, type, address and a Companies House URL per hit. Use for UK entity existence/status; use companies_house_company to fetch one record by number. Free key required.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
queryYesCompany name or partial name

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
dataYesSource payload; fields vary per tool
sourceYesHuman-readable upstream source name
retrievedAtYesISO-8601 timestamp of retrieval

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changed
    • addedInput schema / properties / query / description
      Added value: +"Company name or partial name"
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "properties": {
+    "data": {
+      "description": "Source payload; fields vary per tool",
+      "type": "object"
+    },
+    "retrievedAt": {
+      "description": "ISO-8601 timestamp of retrieval",
+      "type": "string"
+    },
+    "source": {
+      "description": "Human-readable upstream source name",
+      "type": "string"
+    }
+  },
+  "required": [
+    "source",
+    "retrievedAt",
+    "data"
+  ],
+  "type": "object"
+}
  2. First observed

TDQS

A4.4/5.0
Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive, open-world, so the safety profile is covered. The description adds genuinely useful context beyond them: it requires a COMPANIES_HOUSE_API_KEY and states that a free key suffices, which is auth guidance an agent needs before calling. It does not cover rate limits or result caps, keeping it short of a 5.

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?

Three dense, front-loaded sentences with the core purpose first. Slightly marred by redundancy: the API key requirement is stated twice ('requires COMPANIES_HOUSE_API_KEY' and 'Free key required').

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?

An output schema exists, yet the description still usefully summarizes the returned fields (company number, status, type, address, URL). Combined with auth requirements and sibling routing, nothing needed to invoke it correctly is missing.

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?

Only one parameter with 100% schema description coverage ('Company name or partial name'). The description's 'by name' adds nothing beyond the schema, so the baseline 3 applies.

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 (Search) and resource (UK Companies House register by name), and explicitly distinguishes itself from the sibling companies_house_company. An agent can select it correctly without opening either schema.

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?

Names the condition ('Use for UK entity existence/status') and the explicit alternative for the other case ('use companies_house_company to fetch one record by number'). This is a textbook when-to-use/when-to-use-something-else instruction.

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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