registry-mcp — national company registries

List supported national company registries

list_countries

Read-onlyIdempotent

List every national company registry this service can answer for right now, with each one's identifier scheme, source URL, licence, supported_includes, and whether the upstream register needs a credential (requires_api_key, api_key_env).

Call it before your first lookup in a country you have not used here, whenever a user names a country you are unsure of, or before guessing an include value — never hard-code a country list of your own, since it grows as modules are added. Stub modules are hidden; only registries that actually answer are listed. No error mode.

Input Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Output Schema

TableJSON Schema

Name	Required	Description	Default
`countries`	No	One row per registry that can answer right now, sorted by country code.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 8, 2026

addedOutput schema / properties / countries / items / properties / supported_includes

Added value: +{
+  "description": "Attachment names this registry declares — the closed set of valid values for `include=[…]` on `lookup_company`, sorted. Empty when this registry offers no attachments today. Lets an agent discover what more it can ask for before it asks (DECISIONS.md D-042(d)); an `include` value outside this list raises `bad_request` naming this same set, never a silently empty block.",
+  "items": {
+    "type": "string"
+  },
+  "title": "Supported Includes",
+  "type": "array"
+}

First observedSep 6, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already cover read-only, idempotent, and non-destructive traits. The description adds genuine value beyond that: stub modules are hidden so only responding registries appear, and there is 'No error mode.' No contradiction with annotations found.

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?

Two purposeful paragraphs front-loading purpose and output, then usage guidance. Slightly longer than strictly necessary, but every sentence earns its place — the usage directives and growth caveat are not filler.

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?

Complete for a parameterless discovery tool. Purpose, output fields, when to invoke, behavioral caveats (stub hiding, no error mode, dynamic growth) are all present, and the output schema covers return-value documentation. Nothing an agent needs to call it correctly is missing.

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?

With zero parameters and schema coverage at 100%, there is nothing the schema must document. The description compensates by detailing what the result contains (identifier scheme, source URL, licence, supported_includes, requires_api_key, api_key_env), giving the agent a clear picture of the payload it will receive.

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 — 'List every national company registry this service can answer for right now' — and enumerates the output fields (identifier scheme, source URL, licence, supported_includes, credential needs). This clearly differentiates it from lookup/search siblings, which operate on individual companies, not on the registry catalog itself.

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?

Gives explicit when-to-use conditions: before first lookup in an unused country, when uncertain about a country, or before guessing an 'include' value. It also issues an imperative — 'never hard-code a country list' — which is a strong usage directive an agent can act on. No exclusions are needed given the broad list-then-lookup workflow.

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

All registry-mcp — national company registries tools Inspect

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