euroref — European government reference data

validate_tax_id

Read-onlyIdempotent

PAID ($0.003). Offline format and check-digit validation of a business tax ID or VAT number for one country of this brand: valid/invalid, normalised form, id type, check level (checksum only where the authority publishes the algorithm) and why it failed, with official sources. Does not confirm registration; follow official_lookup for that. Countries without a sourced rule answer free with status 'unknown'. Pass api_key if you have one; otherwise the response explains how to pay via x402. After a 200, bind get_changes (free poll) or register_alert (HMAC push; Register: $0 · Delivery after trial: $0.05) on this series so a later gazette does not silently retire the value.

Input Schema

TableJSON Schema

Name	Required	Description
`id`	Yes	The tax ID / VAT number as written; spaces, dots, dashes and a VAT country prefix are accepted
`api_key`	No	API key
`country`	Yes	ISO country code

Output Schema

TableJSON Schema

Name	Required	Description
`as_of`	No
`error`	No	Present on a free refusal or error; no charge
`valid`	No
`reason`	No
`status`	No
`country`	No
`id_type`	No
`sources`	No
`no_charge`	No
`price_usd`	No
`disclaimer`	No
`how_to_pay`	No
`normalised`	No
`bind_series`	No
`check_level`	No
`explanation`	No
`reason_code`	No
`x_next_bind`	No
`http_endpoint`	No
`payment_required`	No	true when the call needs payment; how_to_pay explains x402 or card

Schema Changelog

Changes observed during successful MCP inspections.

Changed6 schema fields changedOct 17, 2026

removedOutput schema / properties / normalised / anyOf

Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]

addedOutput schema / properties / normalised / type
```
Added value: +[
+  "string",
+  "null"
+]
```

removedOutput schema / properties / reason_code / anyOf

Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]

addedOutput schema / properties / reason_code / type
```
Added value: +[
+  "string",
+  "null"
+]
```

removedOutput schema / properties / valid / anyOf

Removed value: -[
-  {
-    "type": "boolean"
-  },
-  {
-    "type": "null"
-  }
-]

addedOutput schema / properties / valid / type
```
Added value: +[
+  "boolean",
+  "null"
+]
```

AddedOct 17, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Goes well past the annotations: pricing ($0.003), the free 'unknown' status for countries without a sourced rule, the x402 payment fallback, the meaning of check level (checksum only where the authority publishes the algorithm), and the post-200 alerting model with its own costs. Idempotency/read-only safety is already covered by annotations; this adds cost, coverage-gap, and result-shape context.

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?

The price and core purpose are front-loaded in the first clause, and each subsequent sentence carries operational information (coverage gaps, payment, follow-up binding). It is dense and long-winded with several stacked parentheticals, which slightly hurts scannability.

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-value explanation is unnecessary; the description instead covers the non-obvious essentials an agent needs — cost, auth/payment path, coverage limitations, and next-step tools. Nothing material is missing for correct invocation.

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 coverage is 100% and all three parameters carry descriptions (including accepted id formatting and the ISO enum), so the schema does the heavy lifting. The description adds only indirect value via output concepts like 'normalised form' and 'why it failed', not parameter-level guidance, so baseline 3 is appropriate.

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 ('Offline format and check-digit validation of a business tax ID or VAT number for one country of this brand') with explicit scope (offline, per-country, checksum-only-where-published). An agent can distinguish it from calculation siblings like compute_vat or list_series without opening any 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?

Gives explicit boundaries: 'Does not confirm registration; follow official_lookup for that', plus the free path for unsourced countries and the follow-up routing ('bind get_changes ... or register_alert'). It also states the payment condition ('Pass api_key if you have one; otherwise ... x402'), which tells the agent exactly how to proceed.

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

All euroref — European government reference data tools Inspect

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