TapTax

Add income or an expense

add_transaction

Record a business income or expense in the signed-in person's TapTax, such as a receipt or a payment. The category is the HMRC self-employment box it belongs in. The same entry added twice within 10 minutes is recorded once.

Input Schema

TableJSON Schema

Name	Required	Description
`date`	Yes	The date on the receipt or of the payment
`type`	Yes
`amount`	Yes	In pounds, VAT included
`category`	Yes	For an expense, its HMRC self-employment box (SA103F): costOfGoods: materials, parts and stock used in the work or sold on, e.g. trade and building suppliers such as Screwfix, Toolstation, City Electrical Factors, Edmundson Electrical, Travis Perkins, Wickes; constructionIndustryScheme: payments to subcontractors under the Construction Industry Scheme; staffCosts: wages, salaries and pension contributions for employees, and payments to non-CIS subcontractors; travelCosts: car, van and travel: fuel, vehicle insurance, servicing and repairs, road tax, parking, tolls, public transport and taxi fares, and hotels and meals on overnight business trips; premisesRunningCosts: rent, business rates, power, heating, water, insurance and security for business premises (never vehicles); maintenanceCosts: repairs and maintenance of business premises, machinery and equipment; adminCosts: phone, broadband, postage, stationery, printing, small office items, and software and app subscriptions such as accounting or tax software (TapTax, Xero, QuickBooks); advertisingCosts: advertising, marketing and website costs; businessEntertainmentCosts: entertaining clients or customers; interest: interest on business loans and overdrafts; financialCharges: bank, overdraft, card and payment-processing charges; badDebt: money owed to the business that will not be paid and was counted as income; professionalFees: accountants, solicitors and other professional fees, and professional indemnity insurance; depreciation: depreciation of equipment (rare in a bank transaction); other: other allowable business costs, e.g. protective clothing, trade and professional body memberships, public liability insurance. For income: turnover (sales and fees) or other (other business income).
`personal`	No	True for a personal (non-business) payment
`description`	Yes	Supplier or client, and what it was for

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 3, 2026

TDQS

A4/5.0

Behavior4/5

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

Annotations already declare a non-read-only, non-destructive, openWorld=false mutation. The description adds genuinely new behavior beyond them: a 10-minute deduplication window ('The same entry added twice within 10 minutes is recorded once'). That is exactly the kind of side-effect nuance the annotations do not carry.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action, then the category semantics, then the dedup caveat. No filler and no repetition of schema content; every sentence carries distinct information.

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?

For a 6-parameter mutation with no output schema, the description covers the action, the categorization rule and the dedup caveat, while annotations carry the safety profile and the schema carries parameter detail. It stops short of stating auth/account requirements or what a successful response confirms, which is a minor gap rather than a blocking one.

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 83% (above the 80% baseline), and the category enum is already documented exhaustively in the schema. The description only adds the framing that a category is 'the HMRC self-employment box it belongs in' and that examples are receipts/payments, which is marginal over the structured data. 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 ('Record a business income or expense in the signed-in person's TapTax') and concretizes it with examples (a receipt or a payment). The verb 'Record' cleanly separates it from list_transactions, update_transaction and create_invoice, so an agent can place it without opening the schema.

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 the usage context (recording business receipts/payments for tax categorization) but never states when to prefer this over create_invoice or prepare_quarterly_update, nor any exclusions. Usage is inferable rather than stated, which is the definition of a 3.

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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