TrueCalci

India GST (regular scheme: CGST, SGST, IGST)

gst_regular

Read-onlyIdempotent

Calculate Indian GST on a supply under the regular scheme: CGST + SGST for an intra-state supply, IGST for an inter-state supply, export or SEZ supply, with optional compensation cess, reverse charge and input tax credit eligibility (Sections 9 and 16-17, CGST Act 2017; Section 5, IGST Act 2017).

Behavior: Deterministic, idempotent calculation with zero external side effects. The rate must be one notified in the GST rule pack in force on as_of_date; the engine refuses a rate the pack does not contain rather than assume one. Exclusive mode adds tax to the amount; inclusive mode extracts it. Returns taxable value, CGST, SGST, IGST, cess, total tax and invoice total.

Usage Guidelines: Use for a registered person under the regular scheme. Do not use for a composition-scheme taxpayer; use gst_composition instead.

Input Schema

Name	Required	Description	Default
`amount`	Yes	Supply value in INR (the taxable value in exclusive mode, the tax-inclusive total in inclusive mode).
`is_rcm`	No	Tax payable by the recipient under reverse charge (Section 9(3)/9(4)).
`as_of_date`	Yes	Civil date YYYY-MM-DD. Selects the rule pack in force on that date. Required: the engine will not assume a date.
`supply_type`	No	Intra-state (CGST + SGST), inter-state (IGST), export or SEZ supply. If omitted, derived from supplier_state and place_of_supply when both are given.
`cess_percent`	No	Compensation cess in percent, where applicable.	0
`itc_eligible`	No	Whether the recipient may claim input tax credit (false for a Section 17(5) blocked credit).
`rate_percent`	Yes	GST rate in percent. Must be a rate notified in the rule pack in force on as_of_date.
`supplier_state`	No	Supplier's state: 2-digit GST state code or state name.
`place_of_supply`	No	Place of supply: 2-digit GST state code or state name.
`calculation_mode`	No	'exclusive' adds GST to amount; 'inclusive' extracts GST from amount.	exclusive

Output Schema

Name	Required	Description	Default
`trace`	No
`is_rcm`	No
`status`	No
`currency`	No
`round_off`	No
`total_tax`	No
`disclaimer`	No
`gst_amount`	No
`base_amount`	No
`cess_amount`	No
`cgst_amount`	No
`igst_amount`	No
`minor_units`	No
`sgst_amount`	No
`supply_type`	No
`cess_percent`	No
`itc_eligible`	No
`net_tax_cost`	No
`rule_ids_used`	No
`calculation_mode`	No
`supply_structure`	No
`statutory_section`	No
`eligible_itc_amount`	No
`gross_invoice_total`	No
`effective_rate_percent`	No
`tax_payable_direct_to_govt`	No
`invoice_payable_to_supplier`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 11, 2026

addedOutput schema / properties / round_off

Added value: +{
+  "type": [
+    "string",
+    "number",
+    "null"
+  ]
+}

Changed1 schema field changedSep 27, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "base_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "calculation_mode": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "cess_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "cess_percent": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "cgst_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "currency": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "disclaimer": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "effective_rate_percent": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "eligible_itc_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "gross_invoice_total": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "gst_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "igst_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "invoice_payable_to_supplier": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "is_rcm": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "itc_eligible": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "minor_units": {
+      "type": [
+        "object",
+        "null"
+      ]
+    },
+    "net_tax_cost": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "rule_ids_used": {
+      "type": [
+        "array",
+        "null"
+      ]
+    },
+    "sgst_amount": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "status": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "statutory_section": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "supply_structure": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "supply_type": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "tax_payable_direct_to_govt": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "total_tax": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "trace": {
+      "type": [
+        "array",
+        "null"
+      ]
+    }
+  },
+  "type": "object"
+}

AddedSep 26, 2026
RemovedSep 24, 2026
AddedSep 11, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint and no side effects, and the description partly restates this ('deterministic, idempotent... zero external side effects'). It earns credit by adding genuinely new behavior: the engine refuses a rate not in the rule pack in force on as_of_date rather than assuming one, and it explains exclusive vs inclusive extraction. Full behavioral burden is not carried because return shape is covered by the output schema.

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 verb+resource, then clearly labeled 'Behavior:' and 'Usage Guidelines:' sections that make scanning easy. It is dense but nearly every sentence is actionable; the only minor waste is the side-effects clause that duplicates the annotations.

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 10-parameter tax calculator with an output schema, the definition covers scheme scope, sibling routing, legal basis, mode semantics and the rate-pack refusal rule. Return values are enumerated and the output schema handles structure, so nothing an agent needs to invoke it correctly is missing.

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 description coverage is 100%, so the schema already documents every parameter including calculation_mode, supply_type derivation and the rate-pack constraint. The description's parameter discussion (exclusive/inclusive, notified rate) largely mirrors that, adding no syntax or format detail beyond the structured fields. Baseline 3 applies.

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 ('Calculate Indian GST on a supply') and enumerates the exact sub-cases it handles (CGST+SGST intra-state, IGST inter-state/export/SEZ, cess, reverse charge, ITC). It also names the scheme it is not ('regular scheme') which, combined with the sibling gst_composition, lets an agent route correctly 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?

The Usage Guidelines block gives an explicit positive condition ('registered person under the regular scheme') and an explicit exclusion with the alternative named ('Do not use for a composition-scheme taxpayer; use gst_composition instead'). This is the exact when/when-not/alternative pattern.

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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