verifica-codice-fiscale

name	verifica-codice-fiscale
description	Validate, decode, and explain an Italian codice fiscale (fiscal code). Checks format, extracts surname, name, birth date, gender, and municipality of birth, and verifies the check digit. Detects common errors (transposed characters, wrong check digit, omocodia variants). Use this skill when a user provides a codice fiscale and wants to verify it is correct, understand what it encodes, or diagnose a mismatch with their personal data.
license	Apache-2.0
compatibility	Works best with the Dichiarino MCP server connected (tool: valida_codice_fiscale). Standalone validation logic is embedded in this skill.
metadata	{"domain":"italian-tax","form":"modello-730","author":"dichiarino"}

Verifica Codice Fiscale

Validate and decode an Italian codice fiscale (16-character alphanumeric fiscal code).

When to activate

Activate when a user:

• Asks "Il mio codice fiscale è corretto?"
• Provides a CF and wants to know what it encodes
• Gets a mismatch error when submitting their 730
• Needs to check a dependent family member's CF

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Structure of the codice fiscale

S S S N N N A A D D D C C C C X
│ │ │ │ │ │ │ │ │ │ │ │ │ │ │ └─ Check character (1)
│ │ │ │ │ │ │ │ │ │ └─────────── Codice comune nascita (4)
│ │ │ │ │ │ │ │ └─────────────── Giorno nascita + sesso (2)
│ │ │ │ │ │ └───────────────── Mese nascita (1 letter)
│ │ │ │ │ └─────────────────── Anno nascita (2 digits)
│ │ │ └───────────────────── Nome consonants (3)
└─────────────────────────── Cognome consonants (3)

Total: 16 characters - uppercase letters and digits.

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Step-by-step validation

1 - Use Dichiarino MCP (if available)

valida_codice_fiscale(codice_fiscale="RSSMRA85M01H501Z")
→ Returns: valid (bool), sesso, data_nascita, codice_comune, errors

2 - Manual validation (fallback)

Step 2a - Format check

• Must be exactly 16 characters
• Regex: ^[A-Z]{6}[0-9LMNPQRSTUV]{2}[ABCDEHLMPRST]{1}[0-9LMNPQRSTUV]{2}[A-Z]{1}[0-9LMNPQRSTUV]{3}[A-Z]{1}$

Step 2b - Decode each field

Pos	Field	How to read
0–2	Cognome	3 consonants; if < 3 consonants, fill with vowels then X
3–5	Nome	If ≥ 4 consonants: take 1st, 3rd, 4th. Else: consonants then vowels then X
6–7	Anno nascita	Last 2 digits of birth year
8	Mese nascita	Letter code (see table below)
9–10	Giorno + sesso	Day 01–31 = male; day 41–71 = female (day − 40)
11–14	Codice comune	Starts with letter for Italian comuni; Z+3 digits for foreign countries
15	Carattere controllo	Computed from positions 0–14

Month letter codes: A=Gen, B=Feb, C=Mar, D=Apr, E=Mag, H=Giu, L=Lug, M=Ago, P=Set, R=Ott, S=Nov, T=Dic

Step 2c - Verify the check digit (position 15)

Odd positions (1,3,5,…): use odd-position lookup table.
Even positions (0,2,4,…): face value (0→0, A→0, B→1 … Z→25).
Sum all 16 partial values → check = chr(ord('A') + (total % 26))

See references/CHECK_DIGIT.md for the full lookup tables.

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Presenting results

Always show:

1. ✅ / ❌ Validity (with reason if invalid)
2. Decoded fields: surname hint, name hint, birth date, gender (M/F), comune/nazione
3. Any detected omocodia substitution (digits replaced with letters)
4. Suggested fix if invalid

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Common errors

Error	Cause	Fix
Wrong check digit	Typo anywhere in the CF	Re-derive from personal data
Day > 40 reported as male	Encoding is correct - female day = day+40	Inform user it's normal
Omocodia variant	Comune has duplicate CFs; Agenzia Entrate substitutes digits with letters	Both variants are valid
Foreign-born	Codice comune = Z + 3 digits (Belcalis table)	Not an error