Warning

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Note: The Warning header is soon to be deprecated; see Warning (https://github.com/httpwg/http-core/issues/139) and Warning: header & stale-while-revalidate (https://github.com/whatwg/fetch/issues/913) for more details.

The Warning general HTTP header contains information about possible problems with the status of the message. More than one Warning header may appear in a response.

Warning header fields can in general be applied to any message, however some warn-codes are specific to caches and can only be applied to response messages.

Header type General header
Forbidden header name no

Syntax

Warning: <warn-code> <warn-agent> <warn-text> [<warn-date>]

Directives

<warn-code>
A three-digit warning number. The first digit indicates whether the Warning is required to be deleted from a stored response after validation.
  • 1xx warn-codes describe the freshness or validation status of the response and will be deleted by a cache after deletion.

  • 2xx warn-codes describe some aspect of the representation that is not rectified by a validation and won't be deleted by a cache after validation unless a full response is sent.

<warn-agent>

The name or pseudonym of the server or software adding the Warning header (might be "-" when the agent is unknown).

<warn-text>
Advisory text describing the error.
<warn-date>
Optional. If more than one Warning header is sent, include a date that matches the Date header.

Warning codes

The HTTP Warn Codes registry at iana.org defines the namespace for warn codes.

Code Text Description
110 Response is Stale A response provided by a cache is stale (the expiration time set for it has passed).
111 Revalidation Failed An attempt to validate the response failed, due to an inability to reach the server.
112 Disconnected Operation The cache is disconnected from the rest of the network.
113 Heuristic Expiration Sent If a cache heuristically chose a freshness lifetime greater than 24 hours and the response's age is greater than 24 hours.
199 Miscellaneous Warning Arbitrary, non-specific warning
214 Transformation Applied Added by a proxy if it applies any transformation to the representation, such as changing the content-coding, media-type or the like.
299 Miscellaneous Persistent Warning Same as 199, but indicating a persistent warning

Examples

Warning: 110 anderson/1.3.37 "Response is stale"

Date: Wed, 21 Oct 2015 07:28:00 GMT 
Warning: 112 - "cache down" "Wed, 21 Oct 2015 07:28:00 GMT"

Specifications

Specification Title
RFC 7234, section 5.5: Warning Hypertext Transfer Protocol (HTTP/1.1): Caching

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
WarningChrome Full support YesEdge Full support YesFirefox Full support YesIE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yes

Legend

Full support  
Full support

See also

Tópicos relacionados
  1. HTTP
  2. Guides:
  3. Resources and URIs
    1. Identifying resources on the Web
    2. Data URIs
    3. Introduction to MIME Types
    4. Complete list of MIME Types
    5. Choosing between www and non-www URLs
  4. HTTP guide
    1. Basics of HTTP
    2. Overview of HTTP
    3. Evolution of HTTP
    4. HTTP Messages
    5. A typical HTTP session
    6. Connection management in HTTP/1.x
    7. Protocol upgrade mechanism
  5. HTTP security
    1. Content Security Policy (CSP)
    2. HTTP Public Key Pinning (HPKP)
    3. HTTP Strict Transport Security (HSTS)
    4. Cookie security
    5. X-Content-Type-Options
    6. X-Frame-Options
    7. X-XSS-Protection
    8. Mozilla web security guidelines
    9. Mozilla Observatory
  6. HTTP access control (CORS)
  7. HTTP authentication
  8. HTTP caching
  9. HTTP compression
  10. HTTP conditional requests
  11. HTTP content negotiation
  12. HTTP cookies
  13. HTTP range requests
  14. HTTP redirects
  15. HTTP specifications
  16. Feature policy
  17. References:
  18. HTTP headers
    1. Accept
    2. Accept-CH
    3. Accept-CH-Lifetime
    4. Accept-Charset
    5. Accept-Encoding
    6. Accept-Language
    7. Accept-Patch
    8. Accept-Ranges
    9. Access-Control-Allow-Credentials
    10. Access-Control-Allow-Headers
    11. Access-Control-Allow-Methods
    12. Access-Control-Allow-Origin
    13. Access-Control-Expose-Headers
    14. Access-Control-Max-Age
    15. Access-Control-Request-Headers
    16. Access-Control-Request-Method
    17. Age
    18. Allow
    19. Alt-Svc
    20. Authorization
    21. Cache-Control
    22. Clear-Site-Data
    23. Connection
    24. Content-Disposition
    25. Content-Encoding
    26. Content-Language
    27. Content-Length
    28. Content-Location
    29. Content-Range
    30. Content-Security-Policy
    31. Content-Security-Policy-Report-Only
    32. Content-Type
    33. Cookie
    34. Cookie2
    35. Cross-Origin-Resource-Policy
    36. DNT
    37. DPR
    38. Date
    39. Device-Memory
    40. Digest
    41. ETag
    42. Early-Data
    43. Expect
    44. Expect-CT
    45. Expires
    46. Feature-Policy
    47. Forwarded
    48. From
    49. Host
    50. If-Match
    51. If-Modified-Since
    52. If-None-Match
    53. If-Range
    54. If-Unmodified-Since
    55. Index
    56. Keep-Alive
    57. Large-Allocation
    58. Last-Modified
    59. Link
    60. Location
    61. Origin
    62. Pragma
    63. Proxy-Authenticate
    64. Proxy-Authorization
    65. Public-Key-Pins
    66. Public-Key-Pins-Report-Only
    67. Range
    68. Referer
    69. Referrer-Policy
    70. Retry-After
    71. Save-Data
    72. Sec-WebSocket-Accept
    73. Server
    74. Server-Timing
    75. Set-Cookie
    76. Set-Cookie2
    77. SourceMap
    78. Strict-Transport-Security
    79. TE
    80. Timing-Allow-Origin
    81. Tk
    82. Trailer
    83. Transfer-Encoding
    84. Upgrade-Insecure-Requests
    85. User-Agent
    86. Vary
    87. Via
    88. WWW-Authenticate
    89. Want-Digest
    90. Warning
    91. X-Content-Type-Options
    92. X-DNS-Prefetch-Control
    93. X-Forwarded-For
    94. X-Forwarded-Host
    95. X-Forwarded-Proto
    96. X-Frame-Options
    97. X-XSS-Protection
  19. HTTP request methods
    1. CONNECT
    2. DELETE
    3. GET
    4. HEAD
    5. OPTIONS
    6. PATCH
    7. POST
    8. PUT
    9. TRACE
  20. HTTP response status codes
    1. 100 Continue
    2. 101 Switching Protocols
    3. 103 Early Hints
    4. 200 OK
    5. 201 Created
    6. 202 Accepted
    7. 203 Non-Authoritative Information
    8. 204 No Content
    9. 205 Reset Content
    10. 206 Partial Content
    11. 300 Multiple Choices
    12. 301 Moved Permanently
    13. 302 Found
    14. 303 See Other
    15. 304 Not Modified
    16. 307 Temporary Redirect
    17. 308 Permanent Redirect
    18. 400 Bad Request
    19. 401 Unauthorized
    20. 402 Payment Required
    21. 403 Forbidden
    22. 404 Not Found
    23. 405 Method Not Allowed
    24. 406 Not Acceptable
    25. 407 Proxy Authentication Required
    26. 408 Request Timeout
    27. 409 Conflict
    28. 410 Gone
    29. 411 Length Required
    30. 412 Precondition Failed
    31. 413 Payload Too Large
    32. 414 URI Too Long
    33. 415 Unsupported Media Type
    34. 416 Range Not Satisfiable
    35. 417 Expectation Failed
    36. 418 I'm a teapot
    37. 422 Unprocessable Entity
    38. 425 Too Early
    39. 426 Upgrade Required
    40. 428 Precondition Required
    41. 429 Too Many Requests
    42. 431 Request Header Fields Too Large
    43. 451 Unavailable For Legal Reasons
    44. 500 Internal Server Error
    45. 501 Not Implemented
    46. 502 Bad Gateway
    47. 503 Service Unavailable
    48. 504 Gateway Timeout
    49. 505 HTTP Version Not Supported
    50. 506 Variant Also Negotiates
    51. 507 Insufficient Storage
    52. 508 Loop Detected
    53. 511 Network Authentication Required
  21. CSP directives
    1. CSP: base-uri
    2. CSP: block-all-mixed-content
    3. CSP: child-src
    4. CSP: connect-src
    5. CSP: default-src
    6. CSP: font-src
    7. CSP: form-action
    8. CSP: frame-ancestors
    9. CSP: frame-src
    10. CSP: img-src
    11. CSP: manifest-src
    12. CSP: media-src
    13. CSP: navigate-to
    14. CSP: object-src
    15. CSP: plugin-types
    16. CSP: prefetch-src
    17. CSP: referrer
    18. CSP: report-to
    19. CSP: report-uri
    20. CSP: require-sri-for
    21. CSP: sandbox
    22. CSP: script-src
    23. CSP: script-src-attr
    24. CSP: script-src-elem
    25. CSP: style-src
    26. CSP: style-src-attr
    27. CSP: style-src-elem
    28. CSP: trusted-types
    29. CSP: upgrade-insecure-requests
    30. CSP: worker-src
  22. CORS errors
    1. Reason: CORS disabled
    2. Reason: CORS header 'Access-Control-Allow-Origin' does not match 'xyz'
    3. Reason: CORS header 'Access-Control-Allow-Origin' missing
    4. Reason: CORS header ‘Origin’ cannot be added
    5. Reason: CORS preflight channel did not succeed
    6. Reason: CORS request did not succeed
    7. Reason: CORS request external redirect not allowed
    8. Reason: CORS request not HTTP
    9. Reason: Credential is not supported if the CORS header ‘Access-Control-Allow-Origin’ is ‘*’
    10. Reason: Did not find method in CORS header ‘Access-Control-Allow-Methods’
    11. Reason: Multiple CORS header 'Access-Control-Allow-Origin' not allowed
    12. Reason: expected ‘true’ in CORS header ‘Access-Control-Allow-Credentials’
    13. Reason: invalid token ‘xyz’ in CORS header ‘Access-Control-Allow-Headers’
    14. Reason: invalid token ‘xyz’ in CORS header ‘Access-Control-Allow-Methods’
    15. Reason: missing token ‘xyz’ in CORS header ‘Access-Control-Allow-Headers’ from CORS preflight channel
  23. Feature-Policy directives
    1. Feature-Policy: accelerometer
    2. Feature-Policy: ambient-light-sensor
    3. Feature-Policy: autoplay
    4. Feature-Policy: battery
    5. Feature-Policy: camera
    6. Feature-Policy: display-capture
    7. Feature-Policy: document-domain
    8. Feature-Policy: encrypted-media
    9. Feature-Policy: fullscreen
    10. Feature-Policy: geolocation
    11. Feature-Policy: gyroscope
    12. Feature-Policy: layout-animations
    13. Feature-Policy: legacy-image-formats
    14. Feature-Policy: magnetometer
    15. Feature-Policy: microphone
    16. Feature-Policy: midi
    17. Feature-Policy: oversized-images
    18. Feature-Policy: payment
    19. Feature-Policy: picture-in-picture
    20. Feature-Policy: publickey-credentials
    21. Feature-Policy: speaker
    22. Feature-Policy: sync-xhr
    23. Feature-Policy: unoptimized-images
    24. Feature-Policy: unsized-media
    25. Feature-Policy: usb
    26. Feature-Policy: vibrate
    27. Feature-Policy: vr
    28. Feature-Policy: wake-lock
    29. Feature-Policy: xr
    30. Feature-Policy: xr-spatial-tracking