ARMS User Experience Monitoring captures network error codes from HTTP responses and platform-specific APIs when monitoring web and mobile applications. These codes appear in your network request analysis dashboards.
Use this reference to identify the root cause of a network error and determine your next debugging step.
HTTP status codes
HTTP status codes follow the standards defined in RFC 9110. Codes in the 4xx range indicate client-side issues, while 5xx codes point to server-side failures.
Client error responses (4xx)
| Error code | Name | Description |
|---|---|---|
| 400 | Bad Request | The server cannot process the request due to a client error such as malformed syntax or invalid parameters. |
| 401 | Unauthorized | The request lacks valid authentication credentials. This code indicates that the client is not authenticated, rather than lacking authorization (see 403). |
| 402 | Payment Required | Reserved for future use. Some APIs use this code to indicate a billing or quota issue. |
| 403 | Forbidden | The server understood the request but refuses to fulfill it. Unlike 401, the client's identity is known but lacks permission. |
| 404 | Not Found | The server cannot find the requested resource. The URL may be incorrect or the resource may have been removed. |
| 405 | Method Not Allowed | The HTTP method used in the request is not supported for the target resource. |
| 406 | Not Acceptable | The server cannot produce a response that matches the client's Accept headers. |
| 407 | Proxy Authentication Required | The client must authenticate with the proxy before the request can proceed. |
| 408 | Request Time-out | The server timed out waiting for the client to complete the request. |
| 409 | Conflict | The request conflicts with the current state of the target resource. |
| 410 | Gone | The resource has been permanently removed and no forwarding address is available. |
| 411 | Length Required | The server requires a Content-Length header in the request. |
| 412 | Precondition Failed | A precondition specified in the request headers evaluated to false on the server. |
| 413 | Request Entity Too Large | The request payload exceeds the size limit that the server is willing to process. |
| 414 | Request-URI Too Large | The request URI exceeds the length that the server is willing to interpret. |
| 415 | Unsupported Media Type | The request payload uses a media type that the server does not support. |
| 416 | Requested range not satisfiable | The range specified in the Range header cannot be fulfilled. |
| 417 | Expectation Failed | The expectation specified in the Expect header cannot be met by the server. |
Server error responses (5xx)
| Error code | Name | Description |
|---|---|---|
| 500 | Internal Server Error | The server encountered an unexpected condition that prevented it from fulfilling the request. |
| 501 | Not Implemented | The server does not support the functionality required to fulfill the request. |
| 502 | Bad Gateway | The server, acting as a gateway or proxy, received an invalid response from an upstream server. |
| 503 | Service Unavailable | The server is temporarily unable to handle the request, typically due to maintenance or overload. |
| 504 | Gateway Time-out | The server, acting as a gateway or proxy, did not receive a timely response from an upstream server. |
| 505 | HTTP Version Not Supported | The server does not support the HTTP version used in the request. |
Android error codes
Android network error codes originate from the WebView and network stack APIs. Negative codes represent connection and network errors, while positive codes indicate SSL certificate issues.
Connection and network errors
| Error code | Name | Category | Description |
|---|---|---|---|
| -1 | Generic error | General | An unspecified network error occurred. |
| -2 | Server or proxy hostname lookup failed | DNS | The DNS lookup for the server or proxy hostname failed. Verify the hostname and check DNS configuration. |
| -3 | Unsupported authentication scheme (not basic or digest) | Authentication | The server requires an authentication scheme that the client does not support. Only Basic and Digest schemes are supported. |
| -4 | User authentication failed on server | Authentication | The credentials provided for server authentication are invalid. |
| -5 | User authentication failed on proxy | Authentication | The credentials provided for proxy authentication are invalid. |
| -6 | Failed to connect to the server | Connection | The client could not establish a TCP connection to the server. The server may be down or the port may be blocked. |
| -7 | Failed to read or write to the server | Connection | The connection was established but data transfer failed. This typically indicates a connection drop during communication. |
| -8 | Connection timed out | Connection | The connection attempt or data transfer exceeded the allowed time limit. |
| -9 | Too many redirects | Redirect | The request was redirected too many times, likely indicating a redirect loop. |
| -10 | Unsupported URI scheme | URI | The URI uses a scheme that the client does not support. |
| -11 | Failed to perform SSL handshake | SSL/TLS | The SSL/TLS handshake with the server failed. This may indicate a protocol mismatch or invalid certificate. |
| -12 | Malformed URL | URI | The URL is not properly formatted. |
| -13 | Generic file error | File | An unspecified file-related error occurred. |
| -14 | File not found | File | The requested file does not exist on the device. |
| -15 | Too many requests during this load | Rate limit | The page triggered too many simultaneous requests during loading. |
| -16 | Resource load was cancelled by Safe Browsing | Security | Google Safe Browsing blocked the resource because it was flagged as potentially harmful. |
Certificate errors
| Error code | Name | Description |
|---|---|---|
| 1 | The certificate has expired | The server's SSL certificate has passed its expiration date. |
| 2 | Hostname mismatch | The certificate's Common Name (CN) or Subject Alternative Name (SAN) does not match the requested hostname. |
| 3 | The certificate authority is not trusted | The certificate was issued by a certificate authority that the device does not trust. |
| 4 | The date of the certificate is invalid | The certificate's validity period has not started yet or has already ended. |
| 5 | A generic error occurred | An unspecified certificate validation error occurred. |
iOS error codes
iOS error codes come from several Apple frameworks, grouped below by domain.
URL loading system errors (NSURLError)
These errors originate from the NSURLSession and NSURLConnection APIs.
Unknown and cancelled requests
| Error code | Name | Description |
|---|---|---|
| -1 | NSURLErrorUnknown | An unknown URL loading error occurred. |
| -999 | NSURLErrorCancelled | The request was explicitly cancelled by the application or the system. |
Background session errors
| Error code | Name | Description |
|---|---|---|
| -995 | NSURLErrorBackgroundSessionRequiresSharedContainer | The background session requires a shared container between the app and its extensions. |
| -996 | NSURLErrorBackgroundSessionInUseByAnotherProcess | Another process is already using the background session. |
| -997 | NSURLErrorBackgroundSessionWasDisconnected | The background session was disconnected from the app. |
URL and connection errors
| Error code | Name | Description |
|---|---|---|
| -1000 | NSURLErrorBadURL | The URL is malformed or uses an unsupported scheme. |
| -1001 | NSURLErrorTimedOut | The request timed out before receiving a response. |
| -1002 | NSURLErrorUnsupportedURL | The URL uses a scheme that the system does not support. |
| -1003 | NSURLErrorCannotFindHost | DNS resolution failed for the specified hostname. |
| -1004 | NSURLErrorCannotConnectToHost | The client could not establish a connection to the server. |
| -1005 | NSURLErrorNetworkConnectionLost | The network connection was lost during the request. |
| -1006 | NSURLErrorDNSLookupFailed | The DNS lookup returned an error. |
| -1007 | NSURLErrorHTTPTooManyRedirects | The request exceeded the maximum number of allowed redirects. |
| -1008 | NSURLErrorResourceUnavailable | The requested resource is not available. |
| -1009 | NSURLErrorNotConnectedToInternet | The device has no active internet connection. |
| -1010 | NSURLErrorRedirectToNonExistentLocation | The redirect points to a URL that does not exist. |
| -1011 | NSURLErrorBadServerResponse | The server returned an invalid or unexpected response. |
| -1012 | NSURLErrorUserCancelledAuthentication | The user cancelled the authentication challenge. |
| -1013 | NSURLErrorUserAuthenticationRequired | The resource requires user authentication. |
| -1014 | NSURLErrorZeroByteResource | The server returned a response with zero bytes of content. |
| -1015 | NSURLErrorCannotDecodeRawData | The response data could not be decoded from its raw format. |
| -1016 | NSURLErrorCannotDecodeContentData | The response data could not be decoded using the expected content encoding. |
| -1017 | NSURLErrorCannotParseResponse | The response could not be parsed. |
Network availability errors
| Error code | Name | Description |
|---|---|---|
| -1018 | NSURLErrorInternationalRoamingOff | The connection failed because international roaming is disabled on the device. |
| -1019 | NSURLErrorCallIsActive | The connection failed because a phone call is active and the data network is unavailable. |
| -1020 | NSURLErrorDataNotAllowed | The connection failed because cellular data usage is not permitted. |
| -1021 | NSURLErrorRequestBodyStreamExhausted | The request body stream was exhausted before delivering all content. |
App Transport Security
| Error code | Name | Description |
|---|---|---|
| -1022 | NSURLErrorAppTransportSecurityRequiresSecureConnection | App Transport Security blocked the request because it requires an HTTPS connection. |
File system errors
| Error code | Name | Description |
|---|---|---|
| -1100 | NSURLErrorFileDoesNotExist | The requested file does not exist at the specified path. |
| -1101 | NSURLErrorFileIsDirectory | The requested path points to a directory, not a file. |
| -1102 | NSURLErrorNoPermissionsToReadFile | The application does not have permission to read the file. |
| -1103 | NSURLErrorDataLengthExceedsMaximum | The data length exceeds the maximum allowed by the system. |
| -1104 | NSURLErrorFileOutsideSafeArea | The file is located outside the designated safe area for access. |
SSL/TLS certificate errors
| Error code | Name | Description |
|---|---|---|
| -1200 | NSURLErrorSecureConnectionFailed | The SSL/TLS handshake failed when establishing a secure connection. |
| -1201 | NSURLErrorServerCertificateHasBadDate | The server certificate has an invalid date (expired or not yet valid). |
| -1202 | NSURLErrorServerCertificateUntrusted | The server certificate is not trusted by the device's trust store. |
| -1203 | NSURLErrorServerCertificateHasUnknownRoot | The server certificate was signed by an unknown root certificate authority. |
| -1204 | NSURLErrorServerCertificateNotYetValid | The server certificate is not yet within its valid date range. |
| -1205 | NSURLErrorClientCertificateRejected | The server rejected the client certificate provided during the handshake. |
| -1206 | NSURLErrorClientCertificateRequired | The server requires a client certificate for authentication. |
Network loading and download errors
| Error code | Name | Description |
|---|---|---|
| -2000 | NSURLErrorCannotLoadFromNetwork | The system cannot load the resource from the network. A cached version may be required. |
| -3000 | NSURLErrorCannotCreateFile | The system failed to create a file for the download. |
| -3001 | NSURLErrorCannotOpenFile | The system failed to open a file for the download. |
| -3002 | NSURLErrorCannotCloseFile | The system failed to close a file after the download. |
| -3003 | NSURLErrorCannotWriteToFile | The system failed to write data to the download file. |
| -3004 | NSURLErrorCannotRemoveFile | The system failed to remove a file during the download process. |
| -3005 | NSURLErrorCannotMoveFile | The system failed to move the downloaded file to its destination. |
| -3006 | NSURLErrorDownloadDecodingFailedMidStream | Decoding of the downloaded data failed during transfer. |
| -3007 | NSURLErrorDownloadDecodingFailedToComplete | Decoding of the downloaded data failed to complete. |
Mach kernel errors
These low-level system errors originate from the Mach kernel and may surface when system resources are exhausted or kernel-level operations fail.
| Error code | Name | Description |
|---|---|---|
| 1 | invalidAddress | An invalid memory address was referenced. |
| 2 | protectionFailure | A memory protection violation occurred. |
| 3 | noSpace | No space is available for the requested operation. |
| 4 | invalidArgument | An invalid argument was passed to a kernel function. |
| 5 | failure | A general kernel operation failure occurred. |
| 6 | resourceShortage | Insufficient system resources to complete the operation. |
| 7 | notReceiver | The target port is not a valid receiver. |
| 8 | noAccess | Access to the requested resource was denied. |
| 9 | memoryFailure | A memory allocation or access failure occurred. |
| 10 | memoryError | A general memory error occurred. |
| 11 | alreadyInSet | The item is already a member of the specified set. |
| 12 | notInSet | The item is not a member of the specified set. |
| 13 | nameExists | The specified name already exists. |
| 14 | aborted | The operation was aborted. |
| 15 | invalidName | The specified name is invalid. |
| 16 | invalidTask | The specified task is invalid. |
| 17 | invalidRight | The specified right is invalid. |
| 18 | invalidValue | The specified value is invalid. |
| 19 | userReferencesOverflow | User references have overflowed. |
| 20 | invalidCapability | The specified capability is invalid. |
| 21 | rightExists | The specified right already exists. |
| 22 | invalidHost | The specified host is invalid. |
| 23 | memoryPresent | The memory is already present. |
| 24 | memoryDataMoved | The memory data has been moved. |
| 25 | memoryRestartCopy | The memory copy operation must be restarted. |
| 26 | invalidProcessorSet | The specified processor set is invalid. |
| 27 | policyLimit | A policy limit has been reached. |
| 28 | invalidPolicy | The specified policy is invalid. |
| 29 | invalidObject | The specified object is invalid. |
| 30 | alreadyWaiting | The thread is already in a waiting state. |
| 31 | defaultSet | The operation involves the default set. |
| 32 | exceptionProtected | The exception is protected. |
| 33 | invalidLedger | The specified ledger is invalid. |
| 34 | invalidMemoryControl | The specified memory control is invalid. |
| 35 | invalidSecurity | The specified security attribute is invalid. |
| 36 | notDepressed | The thread is not in a depressed state. |
| 37 | terminated | The task or thread has been terminated. |
| 38 | lockSetDestroyed | The lock set has been destroyed. |
| 39 | lockUnstable | The lock is in an unstable state. |
| 40 | lockOwned | The lock is owned by another thread. |
| 41 | lockOwnedSelf | The lock is already owned by the current thread. |
| 42 | semaphoreDestroyed | The semaphore has been destroyed. |
| 43 | rpcServerTerminated | The RPC server has been terminated. |
| 44 | rpcTerminateOrphan | The orphaned RPC request was terminated. |
| 45 | rpcContinueOrphan | The orphaned RPC request continues execution. |
| 46 | notSupported | The requested operation is not supported. |
| 47 | nodeDown | The target node is unreachable or down. |
| 48 | notWaiting | The thread is not in a waiting state. |
| 49 | operationTimedOut | The kernel operation timed out. |
| 50 | codesignError | A code signature validation error occurred. |
| 51 | policyStatic | The policy is static and cannot be changed. |
Foundation framework errors (NSError)
These errors originate from the Apple Foundation framework and cover file operations, data handling, and system services.
File read errors
| Error code | Name | Description |
|---|---|---|
| 255 | NSFileLockingError | A file locking operation failed. |
| 256 | NSFileReadUnknownError | An unknown error occurred while reading a file. |
| 257 | NSFileReadNoPermissionError | The application does not have permission to read the file. |
| 258 | NSFileReadInvalidFileNameError | The file name is invalid. |
| 259 | NSFileReadCorruptFileError | The file is corrupted and cannot be read. |
| 260 | NSFileReadNoSuchFileError | The specified file does not exist. |
| 261 | NSFileReadInapplicableStringEncodingError | The string encoding used to read the file is not applicable. |
| 262 | NSFileReadUnsupportedSchemeError | The URI scheme is not supported for file reading. |
| 263 | NSFileReadTooLargeError | The file is too large to read into memory. |
| 264 | NSFileReadUnknownStringEncodingError | The string encoding of the file cannot be determined. |
File write errors
| Error code | Name | Description |
|---|---|---|
| 512 | NSFileWriteUnknownError | An unknown error occurred while writing to a file. |
| 513 | NSFileWriteNoPermissionError | The application does not have permission to write to the file. |
| 514 | NSFileWriteInvalidFileNameError | The file name is invalid for writing. |
| 516 | NSFileWriteFileExistsError | A file already exists at the specified path. |
| 517 | NSFileWriteInapplicableStringEncodingError | The string encoding used for writing is not applicable. |
| 518 | NSFileWriteUnsupportedSchemeError | The URI scheme is not supported for file writing. |
| 640 | NSFileWriteOutOfSpaceError | The disk does not have enough space to complete the write operation. |
| 642 | NSFileWriteVolumeReadOnlyError | The volume is read-only and cannot be written to. |
File manager errors
| Error code | Name | Description |
|---|---|---|
| 768 | NSFileManagerUnmountUnknownError | An unknown error occurred while unmounting a volume. |
| 769 | NSFileManagerUnmountBusyError | The volume cannot be unmounted because it is in use. |
Data validation and formatting errors
| Error code | Name | Description |
|---|---|---|
| 1024 | NSKeyValueValidationError | A key-value coding validation error occurred. |
| 2048 | NSFormattingError | A data formatting error occurred. |
User and feature errors
| Error code | Name | Description |
|---|---|---|
| 3072 | NSUserCancelledError | The user cancelled the operation. |
| 3328 | NSFeatureUnsupportedError | The requested feature is not supported on this platform or configuration. |
Executable errors
| Error code | Name | Description |
|---|---|---|
| 3584 | NSExecutableNotLoadableError | The executable cannot be loaded. |
| 3585 | NSExecutableArchitectureMismatchError | The executable's architecture does not match the current processor. |
| 3586 | NSExecutableRuntimeMismatchError | The executable requires a different runtime version. |
| 3587 | NSExecutableLoadError | An error occurred while loading the executable. |
| 3588 | NSExecutableLinkError | An error occurred while linking the executable. |
Property list errors
| Error code | Name | Description |
|---|---|---|
| 3840 | NSPropertyListReadCorruptError | The property list is corrupted and cannot be read. |
| 3841 | NSPropertyListReadUnknownVersionError | The property list uses an unknown version format. |
| 3842 | NSPropertyListReadStreamError | An error occurred while reading the property list from a stream. |
| 3851 | NSPropertyListWriteStreamError | An error occurred while writing the property list to a stream. |
| 3852 | NSPropertyListWriteInvalidError | The data is invalid and cannot be written as a property list. |
iCloud (ubiquitous file) errors
| Error code | Name | Description |
|---|---|---|
| 4353 | NSUbiquitousFileUnavailableError | The iCloud file is not currently available for download. |
| 4354 | NSUbiquitousFileNotUploadedDueToQuotaError | The file was not uploaded to iCloud because the storage quota is exceeded. |
| 4355 | NSUbiquitousFileUbiquityServerNotAvailable | The iCloud server is not available. |
Coder errors
| Error code | Name | Description |
|---|---|---|
| 4864 | NSCoderReadCorruptError | The archived data is corrupted and cannot be decoded. |
| 4865 | NSCoderValueNotFoundError | The expected value was not found in the archived data. |
| 4866 | NSCoderInvalidValueError | The value in the archived data is invalid. |
On-demand resource errors
| Error code | Name | Description |
|---|---|---|
| 4992 | NSBundleOnDemandResourceOutOfSpaceError | There is not enough disk space to download the on-demand resource. |
| 4993 | NSBundleOnDemandResourceExceededMaximumSizeError | The on-demand resource exceeds the maximum allowed size. |
| 4994 | NSBundleOnDemandResourceInvalidTagError | The specified tag for the on-demand resource is invalid. |
CloudKit sharing errors
| Error code | Name | Description |
|---|---|---|
| 5120 | NSCloudSharingNetworkFailureError | A network failure occurred during a CloudKit sharing operation. |
| 5121 | NSCloudSharingQuotaExceededError | The CloudKit sharing quota is exceeded. |
| 5122 | NSCloudSharingTooManyParticipantsError | The share has reached the maximum number of participants. |
| 5123 | NSCloudSharingConflictError | A conflict occurred during a CloudKit sharing operation. |
| 5124 | NSCloudSharingNoPermissionError | The user does not have permission for the CloudKit sharing operation. |
| 5375 | NSCloudSharingOtherError | An unspecified CloudKit sharing error occurred. |