name	mask-card
description	Maintains the @ekaone/mask-card TypeScript library (credit card masking). Use when working on PAN/credit card masking, maskCard/maskCardAuto/detectCardType/isValidCard changes, PCI display guidance (first 6 + last 4), docs/examples, Vitest tests, tsup builds, versioning, or npm publishing for this repo.

mask-card (project skill)

Scope

This repository is @ekaone/mask-card: a zero-dependency TypeScript library for masking card numbers for display/logging and light validation (Luhn + optional length).

Core exported capabilities (high-level):

maskCard(input, options?)
maskCardAuto(input, options?) (brand-typical grouping; normalized spaces; forces preserveSpacing=false)
maskCardBatch(cards, options?)
detectCardType(input) and getCardTypeGrouping(cardType)
isValidCardLuhn(input) and isValidCard(input, checkLength?)
helpers: getCardLast, getCardFirst, getCardLast4, getCardFirst6

Non-negotiables (security + correctness)

Do not add features that encourage storing, logging, or transmitting full PANs.
Keep defaults aligned with common PCI display guidance: show last 4 digits by default.
If adding new examples/docs, avoid printing full PANs; use test numbers and show masked output.
Preserve behavior documented in README.md unless intentionally changed; if changed, update docs + tests together.

Workflows

Implementing a change (code + tests + docs)

Identify affected functions and update behavior in a backward-compatible way when possible.
Add/adjust Vitest tests for:
- separators stripping vs preserveSpacing
- grouping behavior (number and number[])
- maskCardAuto grouping per brand
- edge cases: empty/nullish input, very short input, all-zeros for Luhn, 13–19 length checks
If output format changes (mask char, spacing, grouping), update README.md examples accordingly.

Local validation commands (this repo)

Run from repo root:

pnpm test
pnpm typecheck
pnpm build

Publishing / release checklist (this repo)

Ensure pnpm test passes (CI parity).
Ensure pnpm build produces dist/ and package entrypoints remain correct (main, module, types, exports in package.json).
Bump version in package.json using semver.
Verify prepublishOnly remains: pnpm clean && pnpm build && pnpm test.
Publish with npm tooling you already use (this repo is configured as public).

Response style when applying this skill

Prefer small, targeted diffs and keep API stable.
When proposing new options, define defaults and update the README option table.
When asked “is this PCI compliant?”, answer in terms of display masking guidance and remind that this library is display-only and does not provide secure storage/tokenization/encryption.

mask-card (project skill)

Scope

This repository is @ekaone/mask-card: a zero-dependency TypeScript library for masking card numbers for display/logging and light validation (Luhn + optional length).

Core exported capabilities (high-level):

maskCard(input, options?)

maskCardAuto(input, options?) (brand-typical grouping; normalized spaces; forces preserveSpacing=false)

maskCardBatch(cards, options?)

detectCardType(input) and getCardTypeGrouping(cardType)

isValidCardLuhn(input) and isValidCard(input, checkLength?)

helpers: getCardLast, getCardFirst, getCardLast4, getCardFirst6

Non-negotiables (security + correctness)

Do not add features that encourage storing, logging, or transmitting full PANs.

Keep defaults aligned with common PCI display guidance: show last 4 digits by default.

If adding new examples/docs, avoid printing full PANs; use test numbers and show masked output.

Preserve behavior documented in README.md unless intentionally changed; if changed, update docs + tests together.

Workflows

Implementing a change (code + tests + docs)

Identify affected functions and update behavior in a backward-compatible way when possible.

Add/adjust Vitest tests for:

separators stripping vs preserveSpacing
grouping behavior (number and number[])
maskCardAuto grouping per brand
edge cases: empty/nullish input, very short input, all-zeros for Luhn, 13–19 length checks

If output format changes (mask char, spacing, grouping), update README.md examples accordingly.

Local validation commands (this repo)

Run from repo root:

pnpm test pnpm typecheck pnpm build

Publishing / release checklist (this repo)

Ensure pnpm test passes (CI parity).

Ensure pnpm build produces dist/ and package entrypoints remain correct (main, module, types, exports in package.json).

Bump version in package.json using semver.

Verify prepublishOnly remains: pnpm clean && pnpm build && pnpm test.

Publish with npm tooling you already use (this repo is configured as public).

Response style when applying this skill

Prefer small, targeted diffs and keep API stable.

When proposing new options, define defaults and update the README option table.

When asked “is this PCI compliant?”, answer in terms of display masking guidance and remind that this library is display-only and does not provide secure storage/tokenization/encryption.