Verified calculation capability

VAT / GST Calculation Capability

Add or remove a single-rate consumption tax (VAT or GST labeling). Gross = Net × (1 + rate/100); Net = Gross × 100 / (100 + rate). · Finance

Capability ID finance.vat · version 1.3.0

Open calculator REST API MCP Evidence Evidence JSON Review policy

Model

Add VAT (gross)

Add VAT (gross): Gross = Net × (1 + rate/100)
VAT amount (from net): VAT = Net × rate/100
Remove VAT (net): Net = Gross × 100 / (100 + rate)
VAT amount (from gross): VAT = Gross − Net

Solve modes: add · remove

Inputs / Outputs

Canonical symbols for this capability. Agent schemas remain the contract.

Symbol	Quantity	Unit	Role
`amount`	Net when adding; gross when removing	—	input
`ratePct`	Tax rate in percent (20 means 20%)	—	input
`net`	—	—	output
`tax`	—	—	output
`gross`	—	—	output

Assumptions / Validity

Declared scope for this capability. Do not use it outside this domain.

Assumptions

Single flat rate on the entered amount
No multi-rate baskets or input-tax credits modeled

Example

One numerical check. The calculator page holds worked steps and FAQ.

Net 100 at 20% → VAT 20, gross 120

Open this example in the calculator

Trust

Review-policy: engine tested — automated tests, sources, version lock, and evidence published. Supplemental to CVP; not Domain Expert Review. See CVP and Review policy.

Tier: Engine tested — catalog token engine_tested
Calculation version: 1.3.0
Evidence tests: 4/4 calculation tests · golden 4/4 · boundary 0/0 · property 0/0
Engine tested: Yes
Source checked: Yes
Supplemental domain review: Not performed
Named expert review: Not performed
Version lock: Supported (409 VERSION_MISMATCH)
Artifact consistency: Build verified · 1.3.0 (workspace artifacts agree)

Production attestation: Embedded snapshot: STALE · Last attested schema matched 1.3.0 snapshot / local build · Semantic contract ✓ · Last attestation PASS · current evidence changed · re-attestation required · Public/cache ✓ · Origin ✓ · Live production status PASS (0 stale; 164 CURRENT) @ 2026-09-16T06:44:24.909Z
Semantic contract: PASS
Evidence attested at: 2026-09-16T06:44:24.203Z
Last production check: 2026-09-16T06:44:24.203Z
Public / cache: PASS
Origin: PASS

Call this capability

Human page, REST, and MCP share the same engine and calculation_version. Build verified hashes workspace artifacts only. After deploy, attest:production GETs canonical URLs twice — the public/cached view an Agent actually hits, and origin — including every /capabilities/{id} HTML page. Public Capability HTML version must match catalog before production attestation passes. Live Trust rows above fetch /.well-known/calculatorx-production-attestation.json and the output schema const. Build hashes: release integrity. That proves currently published page / engine / schema / evidence / MCP agree — not that a historical version is independently immutable. Reference Calculation Standard — Production surface contract 4/4.

Tool id: vat
Engine: vat
REST: POST /api/v1/calc/vat
MCP: execute_calculation with capability_id: "finance.vat"
Agent input schema: Canonical (MCP / Agent)
Output schema: JSON Schema (latest)
Versioned input schema: Immutable pin (1.3.0)
Versioned output schema: Immutable pin (1.3.0)

Operations

Declared calculation modes for this capability.

add
remove

References

Human-readable sources plus CVP reference evidence classes.

Sources

OECD International VAT/GST Guidelines — value-added tax as a consumption tax on the value added
HMRC VAT guide (UK, conceptual) — gross = net × (1 + rate); net = gross / (1 + rate)

Try with an agent

Inspect this capability via same-origin MCP, then call execute_calculation.

curl -sS -X POST 'https://www.calculatorx.com/mcp' \
  -H 'Content-Type: application/json' \
  -H 'MCP-Protocol-Version: 2026-07-28' \
  -H 'Mcp-Method: tools/call' \
  -H 'Mcp-Name: inspect_capability' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"inspect_capability","arguments":{"capability_id":"finance.vat"}}}'

Inspect the trust tier and required assurance level before execution. Pin calculation_version (1.3.0) when reproducibility matters. Full protocol notes: MCP docs.