YouTube SEO Metadata Pack

Validates a complete YouTube metadata set against the real published limits.

THE SILENT FAILURE. YouTube TRUNCATES rather than rejecting. A title over the limit is cut in search results. A description over the limit is cut. And the tag limit is a TOTAL character budget across ALL tags, not per tag — so everything past the budget is silently discarded, which almost nobody accounts for. Nothing errors. The upload succeeds. The creator never learns their last eleven tags were thrown away.

Every limit is cited to YouTube's own documentation in a comment beside the constant. Character counting is done in the unit the platform actually uses, and the choice is documented: naive .length counts UTF-16 code units, so an emoji costs two and an astral character can be cut in half.

Given a prioritised tag list and the total budget, it returns which tags fit AND NAMES the ones dropped. Silently returning a shorter list is the bug.

VERIFIED: 33 tests, 10 deliberate defects applied to the real source, 9 caught and 1 proved to change no observable behaviour (a boundary check whose case the emptiness fallback beside it already covers) — the proofs ship in mutations.json. Every mutation was observed FAILING before the source was restored — a test never seen to fail is a decoration.

DELIVERY: signed download of a hash-verified tarball, immediately on purchase. Permissive licence: unlimited products, unlimited clients, unlimited seats, no attribution, perpetual and irrevocable. One restriction, do not republish the source as source.

Interface

What you call, and what comes back. Types and signatures only — the implementation ships with the source.

  export function utf16Length(value: string): number;
  export function utf8ByteLength(value: string): number;
  export function tagCost(tag: string): number;
  export function tagsTotalCost(tags: readonly string[]): number;
  export function fitTagsToBudget( tags: readonly string[], budget: number = TAGS_TOTAL_MAX_CHARS ): TagFitResult;
  export function fitToCharBudget(value: string, maxChars: number): FitResult;
  export function fitToByteBudget(value: string, maxBytes: number): FitResult;
  export function validateTitle(title: string, maxChars: number = TITLE_MAX_CHARS): Violation[];
  export function validateDescription( description: string, maxBytes: number = DESCRIPTION_MAX_BYTES ): Violation[];
  export function validateTags( tags: readonly string[], budget: number = TAGS_TOTAL_MAX_CHARS ): Violation[];
  export function validateMetadataSet(set: MetadataSet): Violation[];

  export type LengthUnit = "utf16-code-units" | "utf8-bytes";