reference-data

compute_vat

Read-onlyIdempotent

PAID ($0.01). VAT breakdown for an amount: net, tax and gross using the country's current statutory rate, including per-levy components where the rate is composite (e.g. Ghana VAT + NHIL + GETFund). mode=add treats the amount as net; mode=extract backs VAT out of a gross amount. Pass api_key if you have one (instant card checkout at /pricing); otherwise the response explains how to pay via x402. The evaluation country is free to try (see list_series). Optional receipt (boolean, default false): on a paid success, include an Ed25519 answer receipt at no extra USDC. An answer receipt is not a series certified extract (GET /v1/certified/{country}/{series} is $0.10 and is not an MCP tool) and is not legal advice. Verify with verify_answer_receipt against /certified/public-key.

Input Schema

Name	Required	Description
`mode`	No	add = amount is net (default); extract = amount is gross
`amount`	Yes	Amount in the country's own currency
`api_key`	No	API key
`country`	Yes	ISO country code
`receipt`	No	Default false. When true, a paid success includes an Ed25519 answer receipt (kind answer_receipt) at no extra USDC. Unpaid 402 and free refusals do not include one. Not a series certified extract (GET /v1/certified/{country}/{series} at $0.10; that SKU is not an MCP tool).

Output Schema

Name	Required	Description
`net`	No
`tax`	No
`rate`	No
`basis`	No
`error`	No	Present on a free refusal or error; no charge
`gross`	No
`status`	No	Answer status, e.g. computed or an honest no-answer status
`country`	No
`receipt`	No	Ed25519 answer receipt when receipt=true on a paid success
`question`	No
`workings`	No
`no_charge`	No
`price_usd`	No
`disclaimer`	No
`how_to_pay`	No
`provenance`	No	Cited official sources behind the answer
`bind_series`	No
`explanation`	No
`label_basis`	No	Inputs and the rule ids that produced the two labels
`x_next_bind`	No
`http_endpoint`	No
`coverage_label`	No	How much of the question is covered: ready = complete; partial = held with a disclosed limitation or default; gap = no number served. Rules at /label-rules
`confidence_label`	No	Evidence verdict derived from source type, verification age and the stale flag (answers: the weakest series read). Rules at /label-rules
`payment_required`	No	true when the call needs payment; how_to_pay explains x402 or card

Schema Changelog

Changes observed during successful MCP inspections.

Changed5 schema fields changedOct 17, 2026

changedInput schema / properties / receipt / description

Previous value: -"Default false. When true, a paid success includes an Ed25519 answer receipt (kind answer_receipt) at no extra USDC. Unpaid 402 and free refusals do not include one. Not a series certified extract (GET /v1/certified/{country}/{series} at $0.25; that SKU is not an MCP tool)."New value: +"Default false. When true, a paid success includes an Ed25519 answer receipt (kind answer_receipt) at no extra USDC. Unpaid 402 and free refusals do not include one. Not a series certified extract (GET /v1/certified/{country}/{series} at $0.10; that SKU is not an MCP tool)."

removedOutput schema / properties / label_basis / properties / source_type / anyOf

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

addedOutput schema / properties / label_basis / properties / source_type / type
```
Added value: +[
+  "string",
+  "null"
+]
```
removedOutput schema / properties / label_basis / properties / verification_age_days / anyOf
```
Removed value: -[
-  {
-    "type": "number"
-  },
-  {
-    "type": "null"
-  }
-]
```
addedOutput schema / properties / label_basis / properties / verification_age_days / type
```
Added value: +[
+  "number",
+  "null"
+]
```

Changed3 schema fields changedOct 13, 2026

addedOutput schema / properties / confidence_label

Added value: +{
+  "description": "Evidence verdict derived from source type, verification age and the stale flag (answers: the weakest series read). Rules at /label-rules",
+  "enum": [
+    "high",
+    "medium",
+    "low"
+  ],
+  "type": "string"
+}

addedOutput schema / properties / coverage_label

Added value: +{
+  "description": "How much of the question is covered: ready = complete; partial = held with a disclosed limitation or default; gap = no number served. Rules at /label-rules",
+  "enum": [
+    "ready",
+    "partial",
+    "gap"
+  ],
+  "type": "string"
+}

addedOutput schema / properties / label_basis

Added value: +{
+  "additionalProperties": {},
+  "description": "Inputs and the rule ids that produced the two labels",
+  "properties": {
+    "confidence_reasons": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "coverage_reasons": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "inputs": {
+      "items": {},
+      "type": "array"
+    },
+    "rules": {
+      "type": "string"
+    },
+    "rules_version": {
+      "type": "string"
+    },
+    "source_type": {
+      "anyOf": [
+        {
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "stale": {
+      "type": "boolean"
+    },
+    "verification_age_days": {
+      "anyOf": [
+        {
+          "type": "number"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    }
+  },
+  "type": "object"
+}

Changed1 schema field changedOct 12, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": {},
+  "description": "VAT breakdown",
+  "properties": {
+    "basis": {},
+    "bind_series": {},
+    "country": {
+      "type": "string"
+    },
+    "disclaimer": {},
+    "error": {
+      "description": "Present on a free refusal or error; no charge"
+    },
+    "explanation": {},
+    "gross": {},
+    "how_to_pay": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "http_endpoint": {
+      "type": "string"
+    },
+    "net": {},
+    "no_charge": {
+      "type": "boolean"
+    },
+    "payment_required": {
+      "description": "true when the call needs payment; how_to_pay explains x402 or card",
+      "type": "boolean"
+    },
+    "price_usd": {
+      "type": "number"
+    },
+    "provenance": {
+      "description": "Cited official sources behind the answer"
+    },
+    "question": {},
+    "rate": {},
+    "receipt": {
+      "description": "Ed25519 answer receipt when receipt=true on a paid success"
+    },
+    "status": {
+      "description": "Answer status, e.g. computed or an honest no-answer status",
+      "type": "string"
+    },
+    "tax": {},
+    "workings": {},
+    "x_next_bind": {}
+  },
+  "type": "object"
+}

Changed1 schema field changedSep 25, 2026

addedInput schema / properties / receipt

Added value: +{
+  "default": false,
+  "description": "Default false. When true, a paid success includes an Ed25519 answer receipt (kind answer_receipt) at no extra USDC. Unpaid 402 and free refusals do not include one. Not a series certified extract (GET /v1/certified/{country}/{series} at $0.25; that SKU is not an MCP tool).",
+  "type": "boolean"
+}

First observedJul 24, 2026

TDQS

A4.8/5.0

Behavior5/5

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

Annotations already cover read-only/idempotent/non-destructive, but the description adds substantial behavior beyond them: the $0.01 price, the x402 payment flow, that the receipt only appears on a paid success (not on 402 or free refusals), that it costs no extra USDC, that it is not a certified extract, and that it is not legal advice with a verification path via verify_answer_receipt. This is unusually complete disclosure for a paid tool.

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 price and the core purpose, then mode semantics, then payment, then the receipt caveat. Every sentence carries distinct information, though the payment/receipt discussion is dense and could be tightened slightly without losing meaning.

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 no explanation. Given the tool's complexity (paid, dual-mode, optional receipt, verification), the description covers pricing, payment, free tier, receipt behavior, and the verification sibling, leaving no gap an agent needs to call it correctly.

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% so the baseline is 3, and the schema already documents mode, amount, api_key, country, and receipt. The description adds real value beyond the schema: it explains the payment consequence of passing api_key, the free-trial country, and that receipt is free on paid success, which the schema's terse 'Default false' line does not convey.

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 ('VAT breakdown for an amount') and immediately disambiguates scope: net/tax/gross from the country's statutory rate, including composite per-levy components (Ghana VAT + NHIL + GETFund). It also distinguishes itself from the non-MCP certified-extract SKU, so an agent can tell it apart from siblings like compute_income_tax and the certified endpoint.

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 mode semantics (add = amount is net, extract = backs VAT out of gross), states when to pass api_key vs rely on the x402 payment explanation, notes the evaluation country is free (routing to list_series), and names the alternative it is not (GET /v1/certified/{country}/{series}). Conditions for each branch are spelled out rather than implied.

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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