A Dutch tax-checking workflow reviews possible deductions and eligibility for individuals, self-employed people, and companies. It checks supporting evidence and official Dutch tax and legal sources.

It is for checking deductions, scheme eligibility, evidence requirements, thresholds, and legal conditions for a specified tax year.

It helps separate likely deductions from uncertain ones and exposes missing documents or conflicting information.

aftrekcheck — Command for Claude Code by johnhout

Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo

git clone --depth 1 https://github.com/johnhout/knowledge-work-belastingzaken

agentmods

npx agentmods add commands/johnhout/knowledge-work-belastingzaken/aftrekcheck

Made for: Claude Code.

Or install belastingadviseur, the plugin that ships this one along with the rest of its 8 skills, 8 commands, 5 MCP servers.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/commands/johnhout/knowledge-work-belastingzaken/aftrekcheck/github.svg)](https://agentmods.dev/commands/johnhout/knowledge-work-belastingzaken/aftrekcheck)

Your own site

<a href="https://agentmods.dev/commands/johnhout/knowledge-work-belastingzaken/aftrekcheck"><img src="https://agentmods.dev/badge/commands/johnhout/knowledge-work-belastingzaken/aftrekcheck/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/commands/johnhout/knowledge-work-belastingzaken/aftrekcheck"><img src="https://agentmods.dev/badge/commands/johnhout/knowledge-work-belastingzaken/aftrekcheck.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 5 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 372 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00005	$0.00372
Opus 5	$0.00003	$0.00186
Sonnet 5	$0.00001	$0.00074
Haiku 4.5	$0.00001	$0.00037

Measured 8d ago against content hash f0e9f23d2c4e, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

aftrekcheck scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 8d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

commands/aftrekcheck.md · 53 lines

What it actually says

Aftrekcheck / Deduction Check

If placeholders are unclear, see CONNECTORS.md.

Important / Belangrijk: This workflow support is not legal or fiscal advice. Require review by a qualified Dutch tax professional.

Assess potential deductions and scheme eligibility for individual and business contexts.

Usage

/belastingadviseur:aftrekcheck <belastingjaar> [doelgroep]

Workflow

Define taxpayer context:

Individual household context, ZZP context, or BV context
Financial and operational facts relevant to deductions

Build deduction candidate list:

Identify likely relevant deduction categories
Distinguish high-confidence vs uncertain candidates

Evidence and eligibility validation:

Map every candidate to required supporting documents
Flag missing evidence or conflicting data

Official-source verification:

Verify qualification criteria, thresholds, and limitations on belastingdienst.nl
Verify legal references on wetten.overheid.nl when statutory wording matters
Cite exact URL and retrieval date

Fallback behavior:

Without connectors, use user-provided data with clear assumptions
Do not label any deduction as final if key eligibility or source verification is missing

Required Output Format (Use Exactly)

Context / Context
Assumptions / Aannames
Required Documents / Benodigde stukken
Step-by-step / Stappenplan
Checks & Risks / Controles en risico's
Next Actions / Volgende acties
Sources (official) / Bronnen (officieel)
Professional Review Disclaimer / Disclaimer deskundige beoordeling

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

8d ago First seen · 53 lines · 5 tokens per session scan A f0e9f23d2c4e

Subscribe to this mod's changes

aftrekcheck is a command published in the GitHub repository johnhout/knowledge-work-belastingzaken (6 stars, last pushed 6mo ago), licensed MIT. It adds 5 tokens to every session and 372 once invoked, about $0.0000 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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