gatsbyjs/gatsby · error

Non-deterministic routing danger: Attempting to create page:

Error message

Non-deterministic routing danger: Attempting to create page: "${page.path}", but page "${alternateSlashPath}" already exists
This could lead to non-deterministic routing behavior

What it means

In createPage (public actions), a new page's path collides with an existing page differing only by trailing slash (e.g. /about vs /about/). Because both would normalize to overlapping routes, this creates non-deterministic routing — which page wins depends on creation order — so Gatsby warns instead of silently overwriting.

Source

Thrown at packages/gatsby/src/redux/actions/public.js:461

  // If the path doesn't have an initial forward slash, add it.
  if (internalPage.path[0] !== `/`) {
    internalPage.path = `/${internalPage.path}`
  }

  const oldPage: Page = store.getState().pages.get(internalPage.path)
  const contextModified =
    !!oldPage && !_.isEqual(oldPage.context, internalPage.context)
  const componentModified =
    !!oldPage && !_.isEqual(oldPage.component, internalPage.component)
  const slicesModified =
    !!oldPage && !_.isEqual(oldPage.slices, internalPage.slices)

  const alternateSlashPath = page.path.endsWith(`/`)
    ? page.path.slice(0, -1)
    : page.path + `/`

  if (store.getState().pages.has(alternateSlashPath)) {
    report.warn(
      chalk.bold.yellow(`Non-deterministic routing danger: `) +
        `Attempting to create page: "${page.path}", but page "${alternateSlashPath}" already exists\n` +
        chalk.bold.yellow(
          `This could lead to non-deterministic routing behavior`
        )
    )
  }

  // just so it's easier to c&p from createPage action creator for now - ideally it's DRYed
  const { updatedAt, ...node } = internalPage
  node.children = []
  node.internal = {
    type: `SitePage`,
    contentDigest: createContentDigest(node),
  }
  node.id = `SitePage ${internalPage.path}`
  const oldNode = getNode(node.id)

View on GitHub (pinned to e85d62f177)

Solutions

1. Normalize paths before createPage: strip or consistently add the trailing slash (use `path === `/` ? ... : trim)` or the slash helper)
2. Find the two createPage calls producing the duplicate and remove/merge one
3. Ensure source data (CMS slugs) doesn't mix trailing-slash variants

When it happens

Trigger: Thrown at packages/gatsby/src/redux/actions/public.js:461 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of gatsbyjs/gatsby@e85d62f177 (2026-08-26). Data as JSON: /api/errors/718db474a318190a. Report an issue: GitHub.