revalidatePath vs revalidateTag: Why cache strategy choice silently breaks Next.js apps

A developer discovered that using revalidatePath to update a single product price was unnecessarily invalidating unrelated cache entries — including filters, categories, and comparison views sharing the same layout. The core distinction is that revalidatePath invalidates everything rendered under a given URL, while revalidateTag invalidates only the cache entries tied to a specific data tag, regardless of which routes use them. This means revalidateTag offers surgical precision for apps where multiple pages share data dependencies, whereas revalidatePath acts as a blunt instrument that can trigger costly unnecessary re-fetches. The mistake often goes undetected visually, surfacing only in build metrics or slower response times. Developers default to revalidatePath because it appears first in official documentation examples, not because it is the right tool for complex, compositional data architectures.