india_validators

Validate, parse and format the identifiers every Indian app asks for: PAN, GSTIN, Aadhaar, IFSC, UPI ID, mobile number and PIN code.

It does more than a regex:

Real checksums: a GSTIN's check character (base 36) and an Aadhaar number's Verhoeff digit, so typos are caught before you call an API
Typed details: the state from a GSTIN, the holder type from a PAN, the bank from an IFSC, the postal zone from a PIN code
Ready for Flutter forms: drop-in TextFormField validators with messages you can override
Forgiving input: handles lower case, spaces, hyphens, +91 and leading zeros the way people actually type them
Pure Dart, no dependencies: works in Flutter apps, on the server and on the web

final gstin = Gstin.tryParse('27AAPFU0939F1ZV');
print(gstin?.state);            // Maharashtra
print(gstin?.pan.holderType);   // PanHolderType.firm

print(Aadhaar.tryParse('2341 2341 2346')?.masked);  // XXXX XXXX 2346
print(IndianMobile.tryParse('098765-43210')?.e164); // +919876543210

Install

dart pub add india_validators

What's supported

Identifier	Class	Checks	Gives you
PAN	`Pan`	Format, holder type	`holderType` (individual, company, firm, trust…)
GSTIN	`Gstin`	Format, state code, embedded PAN, check character	`state`, `stateCode`, `pan`, `entityCode`
Aadhaar	`Aadhaar`	Format, Verhoeff check digit	`formatted`, `masked`
IFSC	`Ifsc`	Format	`bankCode`, `branchCode`
UPI ID	`UpiId`	Format	`username`, `handle`
Mobile number	`IndianMobile`	Format, 6–9 start	`e164`, `formatted`, `nationalNumber`
PIN code	`Pincode`	Format	`zone` (India Post postal zone)

Every class has tryParse(input), which returns null for invalid input, and isValid(input).

Flutter forms

IndiaValidators has a validator for each identifier, shaped for TextFormField:

Form(
  child: Column(
    children: [
      TextFormField(
        decoration: const InputDecoration(labelText: 'PAN'),
        validator: IndiaValidators.pan,
      ),
      TextFormField(
        decoration: const InputDecoration(labelText: 'GSTIN (optional)'),
        validator: (value) => IndiaValidators.gstin(value, required: false),
      ),
      TextFormField(
        decoration: const InputDecoration(labelText: 'Mobile'),
        keyboardType: TextInputType.phone,
        validator: (value) => IndiaValidators.mobile(
          value,
          message: 'Please enter a 10-digit mobile number',
        ),
      ),
    ],
  ),
)

Each validator returns null when the value is fine, and otherwise an error message. Pass message and emptyMessage to use your own wording or another language.

What validation can and can't tell you

These checks catch typos and malformed input on the device, for free and instantly. They can't tell you that a PAN, GSTIN, Aadhaar number, bank branch or UPI account actually exists or belongs to the user. For that, use the official verification APIs (the GST portal, NSDL/UTIITSL for PAN, UIDAI-authorised KYC providers, your payment gateway).

A few specifics:

PAN: the Income Tax Department doesn't publish the algorithm for the last character, so only the format and holder type are checked.
GSTIN: covers regular taxpayer GSTINs. Special formats, such as UINs for embassies, non-resident taxpayers and TDS/TCS registrations, aren't accepted.
Aadhaar: the Verhoeff digit catches every single-digit typo and every swap of two neighbouring digits. Aadhaar numbers are sensitive: toString() returns the masked form so they don't end up in logs by accident. Show masked, and only store value if you must and are allowed to.

Contributing

Issues and pull requests are welcome, especially new identifiers (vehicle registration, voter ID, passport) with references for their format.

About the author

Built by Chandra ObulaReddy, a Flutter architect who has shipped FinTech, HRMS and e-commerce apps across India.