reference-data

compute_income_tax

Read-onlyIdempotent

PAID ($0.02). Statutory income tax on a TAXABLE-income figure using the country's verified marginal bracket schedule, with full per-bracket workings, effective rate and marginal rate. You pass the amount in local currency. IMPORTANT: this is tax on taxable income, NOT net take-home pay — reliefs/allowances and social-security contributions are the caller's concern and are not applied (see the response scope_note). 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
`api_key`	No	API key (bypasses x402; metered for invoicing)
`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).
`taxable_income`	Yes	Taxable income in the country's local currency, in the schedule's own period basis (annual for most; monthly for Côte d'Ivoire, Uganda, Ethiopia, Costa Rica)

Output Schema

Name	Required	Description
`tax`	No
`basis`	No
`error`	No	Present on a free refusal or error; no charge
`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
`breakdown`	No
`no_charge`	No
`price_usd`	No
`disclaimer`	No
`how_to_pay`	No
`provenance`	No	Cited official sources behind the answer
`scope_note`	No
`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
`marginal_rate`	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
`effective_rate`	No
`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": "Income tax on taxable income with per-bracket workings",
+  "properties": {
+    "basis": {},
+    "bind_series": {},
+    "breakdown": {},
+    "country": {
+      "type": "string"
+    },
+    "disclaimer": {},
+    "effective_rate": {},
+    "error": {
+      "description": "Present on a free refusal or error; no charge"
+    },
+    "explanation": {},
+    "how_to_pay": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "http_endpoint": {
+      "type": "string"
+    },
+    "marginal_rate": {},
+    "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": {},
+    "receipt": {
+      "description": "Ed25519 answer receipt when receipt=true on a paid success"
+    },
+    "scope_note": {},
+    "status": {
+      "description": "Answer status, e.g. computed or an honest no-answer status",
+      "type": "string"
+    },
+    "tax": {},
+    "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"
+}

Changed1 schema field changedJul 24, 2026

changedInput schema / properties / country / enum

Previous value: -[
-  "au",
-  "nz"
-]New value: +[
+  "au",
+  "fj",
+  "nz",
+  "pg",
+  "sb",
+  "to",
+  "vu",
+  "ws"
+]

First observedJul 20, 2026

TDQS

A4.8/5.0

Behavior5/5

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

Goes well beyond the readOnly/idempotent annotations: discloses the $0.02 price, the x402 payment fallback and api_key bypass with /pricing checkout, the 402 behavior for unpaid calls, the optional Ed25519 receipt at no extra USDC, and the legal-advice disclaimer. These are operational traits annotations cannot express.

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 core computation before billing mechanics, and each sentence is informative. It is dense and carries some commercial detail (pricing endpoint, certified-extract aside) that pushes length beyond the minimum an agent needs.

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?

For a paid, read-only compute tool with a full output schema, everything an agent needs is present: input basis, currency/period caveat, payment paths, receipt semantics, and scope exclusions. Return values need not be described since the output schema exists, and the description still previews them.

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 description coverage is 100%, so the 3 baseline applies, but the description adds real framing: api_key is optional ('pass api_key if you have one') with an alternative payment path, and the receipt flag's paid-success-only scope is contextualized. Country/income semantics are largely restated from the schema rather than extended.

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?

Names a specific verb (compute) and resource (statutory income tax) and defines the exact input basis ('tax on a TAXABLE-income figure using the country's verified marginal bracket schedule'). It also states the outputs (per-bracket workings, effective rate, marginal rate), which cleanly separates it from siblings like compute_vat and compute_employment_cost.

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?

Explicitly states when NOT to expect results from this tool ('NOT net take-home pay — reliefs/allowances and social-security contributions are the caller's concern'), points to the scope_note, and names adjacent tools/paths (list_series for the free country, verify_answer_receipt for verification, the certified-extract endpoint as a separate non-MCP SKU). The free-vs-paid condition is also spelled out.

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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