A stock API can return a valid price for the wrong instrument if an integration treats a ticker as a universal identifier. Compare providers on their ability to resolve the requested instrument, retain exchange and currency context, and reject ambiguous mappings before scoring speed or cost. A small identity contract and deliberately conflicting test fixtures make these differences visible without pretending that a successful request proves historical coverage or entitlement.

Resolve the instrument before trusting its price

For a multi-market watchlist, the first acceptance question is whether each response belongs to the security the user selected. A ticker string alone is not a complete identity contract. A market suffix can help distinguish a provider's symbol namespace, but it should not be silently treated as a globally stable instrument identifier.

Store the provider's exact symbol alongside the expected market or exchange and currency.…