Ekwo OS — open source accounting: ledger, invoices and VAT on your own Supabase or Postgres

VAT instalments of a period

instalment_plan

Read-only

The payments on account of a declaration that the VAT scheme a company recorded asks for during its period — a simplified scheme pays part of the year's tax before filing the annual return — with what was due, what was paid and what is outstanding. The schedule, the percentages and the box of the previous year they are read on are country pack data; no country rule lives in this tool. It reads; it pays nothing.

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": {
      "company_id": "<company_id>",
      "from": "<from>",
      "to": "<to>"
    },
    "name": "instalment_plan"
  }
}

Input Schema

Name	Required	Description
`to`	Yes	Last day of that period.
`from`	Yes	First day of the period of the declaration the instalments are paid on account of — usually 1 January.
`company_id`	Yes	The company to work in. Ask list_companies if unsure.

Schema Changelog

Changes observed during successful MCP inspections.

Changed7 schema fields changedOct 27, 2026

addedInput schema / properties / company_id / description

Added value: +"The company to work in. Ask list_companies if unsure."

addedInput schema / properties / company_id / format
```
Added value: +"uuid"
```

addedInput schema / properties / company_id / pattern

Added value: +"^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$"

addedInput schema / properties / from / description

Added value: +"First day of the period of the declaration the instalments are paid on account of — usually 1 January."

addedInput schema / properties / from / pattern
```
Added value: +"^\\d{4}-\\d{2}-\\d{2}$"
```
addedInput schema / properties / to / description
```
Added value: +"Last day of that period."
```
addedInput schema / properties / to / pattern
```
Added value: +"^\\d{4}-\\d{2}-\\d{2}$"
```

AddedOct 25, 2026

TDQS

B3.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description reinforces this with 'It reads; it pays nothing.' Beyond that it adds genuinely new context: the schedule, percentages and prior-year box are country pack configuration, and no country rule is hardcoded in the tool. That tells the agent results vary by pack and where to look when figures seem off.

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

Conciseness2/5

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

A single long, dash-laden sentence that buries the point: the core fact (this returns a VAT instalment schedule with due/paid/outstanding) arrives after a hard-to-parse subordinate clause. The most useful operational note (country pack data, read-only) trails at the end. Restructuring into short front-loaded sentences would improve it substantially.

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?

There is no output schema, and the description does state what comes back — what was due, what was paid, what is outstanding. Combined with the country pack caveat and the read-only statement, an agent has enough to call it correctly. Minor gap: nothing about behaviour when a company is not on a simplified scheme.

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 from/to/company_id are already documented in the schema. The description echoes the period-of-declaration framing but adds no format, defaults, or edge-case guidance (e.g. what happens for a non-simplified scheme) beyond the schema. Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose3/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description does convey the resource: the schedule of VAT payments on account for a declaration period, with due/paid/outstanding amounts. But it opens with a convoluted noun phrase ("The payments on account of a declaration that the VAT scheme a company recorded asks for...") and never names a verb, and it does not distinguish itself from siblings like vat_return or tax_estimate, which cover adjacent VAT territory.

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?

Usage is only implied: an agent can infer it is for inspecting instalment obligations of a VAT period. There is no explicit statement of when to use this instead of vat_return, tax_estimate or tax_computations. The one negative constraint ('it pays nothing') steers away from payment actions, but no alternative is named.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All Ekwo OS — open source accounting: ledger, invoices and VAT on your own Supabase or Postgres tools Inspect

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