Error reference

Application failures set MCP isError: true and return bounded JSON text:

json

{
  "ok": false,
  "error": {
    "code": "PAGE_NOT_FOUND",
    "message": "The requested browser page was not found in the addressed session",
    "operationId": "…"
  }
}

Code	Meaning / next step
`SESSION_NOT_FOUND`	rediscover or create the session
`SESSION_NOT_READY`	session has not reached ready state
`SESSION_CLOSING`	stop submitting work to this session
`SESSION_CLOSED`	create a new session
`PAGE_NOT_FOUND`	verify both IDs and page ownership
`INVALID_ARGUMENT`	correct the request schema/value
`OPERATION_TIMEOUT`	inspect state, use a deterministic wait, or adjust bounded timeout
`OPERATION_CANCELLED`	caller cancelled the request
`NAVIGATION_FAILED`	inspect safe reason/URL context and network conditions
`ELEMENT_NOT_FOUND`	recapture state or correct the locator
`LOCATOR_AMBIGUOUS`	make the locator unique
`STALE_ELEMENT_REFERENCE`	capture a new snapshot/ref
`STALE_SNAPSHOT_CURSOR`	capture a new snapshot
`BROWSER_ERROR`	operation failed; install Chromium if remediation says so
`BROWSER_DISCONNECTED`	existing sessions cannot recover; restart and recreate them
`LIMIT_EXCEEDED`	reduce requested/captured data or revise configured budget
`RUNTIME_SHUTTING_DOWN`	stop submitting work and reconnect later
`SAVED_STATE_NOT_FOUND`	list states or use another ID
`PERSISTENCE_DISABLED`	enable persistence or omit state operations
`INTERNAL_ERROR`	unexpected safe failure; gather bounded diagnostics

Browser failures may include only an allowlisted reason: timeout, dns, connection, tls, invalid_url, locator_ambiguous, element_not_found, or other. Public URLs exclude credentials, queries, and fragments. Raw Playwright messages, causes, stacks, tokens, and form values are not returned.

A failed operation does not poison the session queue. Do not automatically retry destructive actions unless the workflow can establish whether the action took effect.

Error reference ​

Error reference