For developers
The same calculations, in your application
The Phynanx API exposes the site's tax simulators: a deterministic calculation, versioned by year, with every step traced to its legal texts.
What the API brings
Deterministic calculation
The same input always gives the same result: no language model computes anything, every amount comes from the engine.
Every step traced and sourced
The response details each calculation step, the formula applied and the texts cited (French tax code, BOFiP, social security code…), with a Légifrance link when available.
Versioned by year
Each simulator carries its tax year and its rules version (rulesVersion): a calculation for a closed year stays identical.
Available simulators
12 simulators are exposed today: income tax (one per tax year), gross → net salary, VAT and real estate wealth tax (IFI).
A real example
Request and response taken from the API (VAT on €1,000 excluding tax), copied as is. $API_URL stands for the API address, provided when access opens.
curl -X POST "$API_URL/v1/calculators/calcul-tva-2025/calculate" \
-H "Content-Type: application/json" \
-d '{"montantHT": "1000"}'{
"slug": "calcul-tva-2025",
"version": "1.0.0",
"legalCorrections": [],
"engineExtensions": [],
"result": {
"montantTVA": "200",
"montantTTC": "1200"
},
"cotisations": [],
"steps": [
{
"id": "calcul_tva",
"descriptionFr": "Application du taux normal de TVA (20 %)",
"formula": "montantHT × 20 %",
"inputs": { "montantHT": "1000" },
"output": "200",
"citations": [
{
"authority": "CGI",
"reference": "art. 278",
"url": "https://www.legifrance.gouv.fr/codes/article_lc/LEGIARTI000026950057/",
"asOfDate": "2014-01-01"
}
],
"moduleId": "fr_tva_standard_2025"
},
{
"id": "calcul_ttc",
"descriptionFr": "Calcul du montant TTC",
"formula": "montantHT + montantTVA",
"inputs": { "montantHT": "1000", "montantTVA": "200" },
"output": "1200",
"citations": [],
"moduleId": "fr_tva_standard_2025"
}
],
"warnings": [],
"rulesVersion": "[email protected]"
}Traceability at the heart of the response
Each step of the response carries its description, formula, inputs, result and citations: enough to show your users the calculation in detail, with the law to back it.
Application du taux normal de TVA (20 %)
montantHT × 20 % = 200
CGI, art. 278 · in force as of 2014-01-01API routes
GET /v1/calculatorsReturns the list of simulators (identifier, name, version).GET /v1/calculators/{slug}Returns a simulator's definition: its form, fields and outputs.GET /v1/calculators/{slug}/legal-basisReturns the legal basis of each box (tax code article, BOFiP doctrine).POST /v1/calculators/{slug}/calculateRuns the full calculation and returns the result, the traced steps, the citations and the warnings.POST /v1/calculators/{slug}/solveRuns an inverse calculation: it finds the input value that reaches a target result.POST /v1/calculators/{slug}/explainExplains the calculation in French or English, with the mechanisms triggered and the texts.
Exposed simulators
| Name | slug |
|---|---|
| Calcul de la TVA 2025 | calcul-tva-2025 |
| Calcul salaire brut → net 2025 | calcul-salaire-brut-net-2025 |
| Calcul salaire brut → net 2026 | calcul-salaire-brut-net-2026 |
| Impôt sur le revenu 2019 | impot-revenu-2019 |
| Impôt sur le revenu 2020 | impot-revenu-2020 |
| Impôt sur le revenu 2021 | impot-revenu-2021 |
| Impôt sur le revenu 2022 | impot-revenu-2022 |
| Impôt sur le revenu 2023 | impot-revenu-2023 |
| Impôt sur le revenu 2024 | impot-revenu-2024 |
| Impôt sur le revenu 2025 | impot-revenu-2025 |
| Impôt sur le revenu 2026 | impot-revenu-2026 |
| Impôt sur la fortune immobilière 2026 | ifi-2026 |
Read the API documentation: route reference and guides in French.
Access
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