Primary Sources

companies_house_company

Read-onlyIdempotent

Fetch one UK company record by company number (requires COMPANIES_HOUSE_API_KEY). Returns the full Companies House profile object (registered office, officers summary, SIC, status). Use after companies_house_search. Free key required.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`number`	Yes	UK company number, e.g. 09446231

Output Schema

TableJSON Schema

Name	Required	Description
`data`	Yes	Source payload; fields vary per tool
`source`	Yes	Human-readable upstream source name
`retrievedAt`	Yes	ISO-8601 timestamp of retrieval

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 3, 2026

addedInput schema / properties / number / description
```
Added value: +"UK company number, e.g. 09446231"
```

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"
+}

First observedOct 3, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds real operational context beyond them: the COMPANIES_HOUSE_API_KEY requirement (auth) and that a free key suffices, which an agent needs before calling.

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?

Front-loaded with the action and resource, then the return shape, then sequencing. Minor redundancy: the key requirement is stated twice ('requires COMPANIES_HOUSE_API_KEY' and 'Free key required'), which is a small waste of an otherwise tight three-sentence block.

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, so return values need not be spelled out, and the annotations cover the safety profile. The description still supplies the auth requirement and the search-then-fetch workflow, leaving nothing an agent needs in order to invoke it correctly.

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 description coverage is 100% and the single parameter is fully documented with an example (09446231), so the schema carries the load. The description adds only the phrase 'by company number', which restates the schema rather than adding syntax or format nuance. 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 (Fetch) and resource (one UK company record) with an explicit identifying key (company number). It is clearly distinguishable from the sibling companies_house_search, which lists rather than fetches a single entity.

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?

Explicitly names the prerequisite/sequencing: 'Use after companies_house_search', which routes the agent from search to detail. It stops short of stating when NOT to use it or naming any alternative detail source, so it is clear context rather than full when/when-not guidance.

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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