End of component comment prerendered property must match the

Error message

End of component comment prerendered property must match the start comment prerender id: '${prerenderId}', '${prerenderEndId}'

What it means

Thrown by validateEndComponentPayload (ComponentDescriptorDiscovery.ts:295) when the end marker's prerenderId does not equal the start marker's prerenderId. Blazor pairs prerendered components by matching these IDs; a mismatch means start and end comments got out of order (e.g. interleaved or duplicated markers).

Source

Thrown at src/Components/Web.JS/src/Services/ComponentDescriptorDiscovery.ts:295

  // Parameter definitions and values come Base64 encoded from the server, since they contain random data and can make the
  // comment invalid. We could unencode them in .NET Code, but that would be slower to do and we can leverage the fact that
  // JS provides a native function that will be much faster and that we are doing this work while we are fetching
  // blazor.boot.json
  payload.parameterDefinitions = payload.parameterDefinitions && atob(payload.parameterDefinitions);
  payload.parameterValues = payload.parameterValues && atob(payload.parameterValues);
}

function validateEndComponentPayload(json: string, prerenderId: string): void {
  const payload = JSON.parse(json) as ComponentEndMarker;
  if (Object.keys(payload).length !== 1) {
    throw new Error(`Invalid end of component comment: '${json}'`);
  }
  const prerenderEndId = payload.prerenderId;
  if (!prerenderEndId) {
    throw new Error(`End of component comment must have a value for the prerendered property: '${json}'`);
  }
  if (prerenderEndId !== prerenderId) {
    throw new Error(`End of component comment prerendered property must match the start comment prerender id: '${prerenderId}', '${prerenderEndId}'`);
  }
}

class ComponentCommentIterator {
  private childNodes: NodeListOf<ChildNode>;

  private currentIndex: number;

  private length: number;

  public currentElement: ChildNode | undefined;

  public constructor(childNodes: NodeListOf<ChildNode>) {
    this.childNodes = childNodes;
    this.currentIndex = -1;
    this.length = childNodes.length;
  }

View on GitHub (pinned to 294cab2f9b)

Solutions

Inspect the raw HTML to verify each start  is immediately followed by its matching .
Disable HTML comment reordering/minification on Blazor pages.
Match framework versions.
Avoid caching prerendered fragments in a way that re-orders markers.

Defensive patterns

Strategy: validation

Validate before calling

function markersArePaired(startPayload: {prerenderId?:string}, endPayload: {prerenderId?:string}): boolean {
  return !!startPayload?.prerenderId && startPayload.prerenderId === endPayload?.prerenderId;
}

Type guard

function isMatchingEnd(startId: string, endPayload: any): boolean {
  return endPayload?.prerenderId === startId;
}

Prevention

Do not reorder HTML comments on Blazor pages.
Avoid caching prerender fragments out of order.
Match framework versions so prerenderId formats agree.

When it happens

Trigger: A start marker's prerenderId differs from the next end marker encountered while iterating; caused by reordered/duplicated prerendered component comments in the DOM.

Common situations: HTML reordering by minifiers/transformers; nested prerendered components whose comments got interleaved incorrectly; duplicated cached prerender fragments; version mismatch in prerenderId format.

Related errors

AI-assisted analysis of dotnet/aspnetcore@294cab2f9b (2026-08-06). Data as JSON: /api/errors/6323b286d6e537c7. Report an issue: GitHub.