RealYield

Calculate Section 24 tax

calculate_section_24_tax

Read-onlyIdempotent

Works out a UK landlord's income tax on rental profit under Section 24, where mortgage interest is not deductible and is replaced by a 20% tax credit. Returns the tax bill, the 20% credit, cashflow after tax, the extra tax compared with full interest relief, and the same figures for all three tax bands.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "annualRent": "<annualRent>"
    },
    "name": "calculate_section_24_tax"
  }
}

Input Schema

Name	Required	Description	Default
`taxBand`	No	The landlord's income tax band: basic (20%), higher (40%) or additional (45%).	higher
`annualRent`	Yes	Gross annual rental income in GBP.
`annualOperatingCosts`	No	Annual allowable costs excluding mortgage interest, in GBP.
`annualMortgageInterest`	No	Annual mortgage interest in GBP.

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 16, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations already establish readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuine behavioral value by enumerating the computed outputs (tax bill, 20% credit, cashflow after tax, extra tax versus full relief, and all three bands), which matters because there is no output schema. It does not state tax-year assumptions or rounding.

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?

A single front-loaded sentence that leads with the domain rule and then lists outputs. Dense but every clause carries information; a slightly tighter split into 'what it does' and 'what it returns' would read better, but nothing is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description correctly compensates by enumerating return fields, and it explains the core calculation rule. Remaining gaps are minor: no stated tax-year, no note on how annualOperatingCosts interacts with the disallowed interest, and no indication that taxBand only changes which figure is headline.

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 all four parameters are already documented, giving a baseline of 3. The description adds marginal nuance that results are also returned for all three tax bands regardless of taxBand, but it does not clarify units, interaction between taxBand and the headline figures, or default behaviour beyond what the schema shows.

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 (calculate) plus the precise domain resource (UK landlord income tax on rental profit under Section 24), including the key mechanic (mortgage interest disallowed, replaced by a 20% credit). This clearly differentiates it from siblings like calculate_capital_gains_tax and calculate_stamp_duty.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when the tool applies (a UK landlord subject to Section 24 with mortgage interest), but never states when to use it versus the sibling calculators or any prerequisites. No alternatives or exclusions are named, so the agent must infer the routing itself.

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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