vercel/next.js · error · Error

You cannot have the slug names "${slug}" and "${nextSlug}" d

Error message

You cannot have the slug names "${slug}" and "${nextSlug}" differ only by non-word symbols within a single dynamic path

What it means

handleSlug throws when two slug names at the same level become identical once non-word characters (\W) are stripped, e.g. [my-post] vs [my_post]. Because params are keyed by normalized names, such names would collide at runtime.

Source

Thrown at packages/next/src/shared/lib/router/utils/sorted-routes.ts:144

          // pages/[id]/index.js
          // Because currently multiple dynamic params on the same segment level are not supported
          if (previousSlug !== nextSlug) {
            // TODO: This error seems to be confusing for users, needs an error link, the description can be based on above comment.
            throw new Error(
              `You cannot use different slug names for the same dynamic path ('${previousSlug}' !== '${nextSlug}').`
            )
          }
        }

        slugNames.forEach((slug) => {
          if (slug === nextSlug) {
            throw new Error(
              `You cannot have the same slug name "${nextSlug}" repeat within a single dynamic path`
            )
          }

          if (slug.replace(/\W/g, '') === nextSegment.replace(/\W/g, '')) {
            throw new Error(
              `You cannot have the slug names "${slug}" and "${nextSlug}" differ only by non-word symbols within a single dynamic path`
            )
          }
        })

        slugNames.push(nextSlug)
      }

      if (isCatchAll) {
        if (isOptional) {
          if (this.restSlugName != null) {
            throw new Error(
              `You cannot use both an required and optional catch-all route at the same level ("[...${this.restSlugName}]" and "${urlPaths[0]}" ).`
            )
          }

          handleSlug(this.optionalRestSlugName, segmentName)
          // slugName is kept as it can only be one particular slugName

View on GitHub (pinned to 0eb3775416)

Solutions

1. Use slug names that differ by more than non-word symbols within one dynamic path.

When it happens

Trigger: Two slug names differ only by non-word symbols.

Common situations: Slugs like 'post-id' and 'post_id' used in the same dynamic path.

AI-assisted analysis of vercel/next.js@0eb3775416 (2026-08-19). Data as JSON: /api/errors/761d0fc58879ade5. Report an issue: GitHub.