vercel/next.js · error

Warning: invalid tags passed to ${description}:

Error message

Warning: invalid tags passed to ${description}: 

What it means

validateTags collects tags that are non-strings or exceed NEXT_CACHE_TAG_MAX_LENGTH and warns with this message, then logs each invalid tag with its reason; invalid tags are excluded from revalidation tagging rather than failing the fetch.

Source

Thrown at packages/next/src/server/lib/patch-fetch.ts:162

      })
    } else {
      // Encode so a non-ASCII tag can be safely serialized into the
      // `x-next-cache-tags` HTTP header without tripping Node's header
      // validation. Length is checked on the raw input above.
      validTags.push(encodeHeaderSafe(tag))
    }

    if (validTags.length > NEXT_CACHE_TAG_MAX_ITEMS) {
      console.warn(
        `Warning: exceeded max tag count for ${description}, dropped tags:`,
        tags.slice(i).join(', ')
      )
      break
    }
  }

  if (invalidTags.length > 0) {
    console.warn(`Warning: invalid tags passed to ${description}: `)

    for (const { tag, reason } of invalidTags) {
      console.log(`tag: "${tag}" ${reason}`)
    }
  }
  return validTags
}

function trackFetchMetric(
  workStore: WorkStore,
  span: Span | undefined,
  ctx: Omit<FetchMetric, 'end' | 'idx'>
) {
  const metric = {
    ...ctx,
    end: performance.timeOrigin + performance.now(),
    idx: workStore.nextFetchId || 0,
  }

View on GitHub (pinned to 0eb3775416)

Solutions

1. Pass only valid cache tag strings (no invalid characters, within length limits) to fetch/revalidate.

When it happens

Trigger: Thrown at packages/next/src/server/lib/patch-fetch.ts:162 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of vercel/next.js@0eb3775416 (2026-08-19). Data as JSON: /api/errors/58b4ce7da7d35994. Report an issue: GitHub.