serverless/serverless · error · ServerlessError

MCP_ENTRY_BUNDLE_MISSING

MCP_ENTRY_BUNDLE_MISSING

Error message

The prebuilt MCP Lambda entry is missing at "${source}". In a source checkout it is a build product: run "npm run build:mcp:entry" in packages/serverless and retry. A released Serverless Framework ships it, so seeing this from an installed version is a bug - please report it at https://github.com/serverless/serverless/issues.

What it means

Error "The prebuilt MCP Lambda entry is missing at "${source}". In a source checkout it is a build product: run "npm run build:mcp:entry" in packages/serverless and retry. A released Serverless Framework ships it, so seeing this from an installed version is a bug - please report it at https://github.com/serverless/serverless/issues." thrown in serverless/serverless.

Source

Thrown at packages/serverless/lib/plugins/aws/mcp/lib/packaging.js:197

 * Copy the prebuilt entry into the service dir and make packaging pick it up.
 *
 * `functionObjects` are the MCP server functions this run packages, and they
 * carry the pattern instead of the service under `package.individually`: a
 * service-level pattern merges into EVERY per-function zip - `getIncludes`
 * unions it into each classic per-function file list, and the esbuild plugin
 * unions it into each per-function zip the same way - which would put the
 * multi-megabyte entry in functions that have no use for it.
 *
 * `source` is injected so the tests do not depend on a built bundle.
 */
export const stageEntry = async ({
  serviceDir,
  servicePackage,
  functionObjects = [],
  source = mcpEntrySourcePath,
}) => {
  if (!existsSync(source)) {
    throw new ServerlessError(
      `The prebuilt MCP Lambda entry is missing at "${source}". In a source checkout it is a build product: run "npm run build:mcp:entry" in packages/serverless and retry. A released Serverless Framework ships it, so seeing this from an installed version is a bug - please report it at https://github.com/serverless/serverless/issues.`,
      'MCP_ENTRY_BUNDLE_MISSING',
      { stack: false },
    )
  }
  const stagedDir = stagedDirOf(serviceDir)
  await assertStageable(stagedDir, source)
  await mkdir(stagedDir, { recursive: true })
  await copyFile(source, path.join(stagedDir, stagedEntryName))
  if (servicePackage.individually !== true) {
    addStagedPattern(servicePackage)
    return
  }
  for (const functionObject of functionObjects) {
    addStagedPattern((functionObject.package = functionObject.package ?? {}))
  }
}

View on GitHub (pinned to b9d7ea51c8)

Solutions

1. In a source checkout, run 'npm run build:mcp:entry' in packages/serverless and retry.
2. If using an installed release, report it at https://github.com/serverless/serverless/issues.

When it happens

Trigger: Thrown at packages/serverless/lib/plugins/aws/mcp/lib/packaging.js:197 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of serverless/serverless@b9d7ea51c8 (2026-08-13). Data as JSON: /api/errors/a6f818bb96abe3d9. Report an issue: GitHub.