304 Not Modified - HTTP | MDN

archived 16 Sep 2017 12:33:35 UTC
The HTTP 304 Not Modified client redirection response code indicates that there is no need to retransmit the requested resources. It is an implicit redirection to a cached resource. This happens when the request method is safe, like a GET or a HEAD request, or when the request is conditional and uses a If-None-Match or a If-Modified-Since header.
The equivalent 200 OK response would have included the headers Cache-Control, Content-Location, Date, ETag, Expires, and Vary.
Many developer tools' network panels of browsers create extraneous requests leading to 304 responses, so that access to the local cache is visible to developers.

StatusEdit

304 Not Modified

SpecificationsEdit

Specification Title
RFC 7232, section 4.1: 304 Not Modified Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests

Browser compatibilityEdit

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic Support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

Compatibility NotesEdit

  • Browser behavior differs if this response erroneously includes a body on persistent connections See 204 No Content for more detail.

See alsoEdit

Document Tags and Contributors

 Contributors to this page: haroldfredshort, mtShaikh, jugglinmike, fscholz, teoli
 Last updated by: haroldfredshort,
See also
  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. References:
  17. HTTP headers
    1. Accept
    2. Accept-Charset
    3. Accept-Encoding
    4. Accept-Language
    5. Accept-Ranges
    6. Access-Control-Allow-Credentials
    7. Access-Control-Allow-Headers
    8. Access-Control-Allow-Methods
    9. Access-Control-Allow-Origin
    10. Access-Control-Expose-Headers
    11. Access-Control-Max-Age
    12. Access-Control-Request-Headers
    13. Access-Control-Request-Method
    14. Age
    15. Allow
    16. Authorization
    17. Cache-Control
    18. Connection
    19. Content-Disposition
    20. Content-Encoding
    21. Content-Language
    22. Content-Length
    23. Content-Location
    24. Content-Range
    25. Content-Security-Policy
    26. Content-Security-Policy-Report-Only
    27. Content-Type
    28. Cookie
    29. Cookie2
    30. DNT
    31. Date
    32. ETag
    33. Expect
    34. Expires
    35. Forwarded
    36. From
    37. Host
    38. If-Match
    39. If-Modified-Since
    40. If-None-Match
    41. If-Range
    42. If-Unmodified-Since
    43. Keep-Alive
    44. Large-Allocation
    45. Last-Modified
    46. Location
    47. Origin
    48. Pragma
    49. Proxy-Authenticate
    50. Proxy-Authorization
    51. Public-Key-Pins
    52. Public-Key-Pins-Report-Only
    53. Range
    54. Referer
    55. Referrer-Policy
    56. Retry-After
    57. Server
    58. Set-Cookie
    59. Set-Cookie2
    60. SourceMap
    61. Strict-Transport-Security
    62. TE
    63. Tk
    64. Trailer
    65. Transfer-Encoding
    66. Upgrade-Insecure-Requests
    67. User-Agent
    68. Vary
    69. Via
    70. WWW-Authenticate
    71. Warning
    72. X-Content-Type-Options
    73. X-DNS-Prefetch-Control
    74. X-Forwarded-For
    75. X-Forwarded-Host
    76. X-Forwarded-Proto
    77. X-Frame-Options
    78. X-XSS-Protection
  18. HTTP request methods
    1. CONNECT
    2. DELETE
    3. GET
    4. HEAD
    5. OPTIONS
    6. PATCH
    7. POST
    8. PUT
  19. HTTP response status codes
    1. 100 Continue
    2. 101 Switching Protocols
    3. 200 OK
    4. 201 Created
    5. 202 Accepted
    6. 203 Non-Authoritative Information
    7. 204 No Content
    8. 205 Reset Content
    9. 206 Partial Content
    10. 300 Multiple Choices
    11. 301 Moved Permanently
    12. 302 Found
    13. 303 See Other
    14. 304 Not Modified
    15. 307 Temporary Redirect
    16. 308 Permanent Redirect
    17. 400 Bad Request
    18. 401 Unauthorized
    19. 403 Forbidden
    20. 404 Not Found
    21. 405 Method Not Allowed
    22. 406 Not Acceptable
    23. 407 Proxy Authentication Required
    24. 408 Request Timeout
    25. 409 Conflict
    26. 410 Gone
    27. 411 Length Required
    28. 412 Precondition Failed
    29. 413 Payload Too Large
    30. 414 URI Too Long
    31. 415 Unsupported Media Type
    32. 416 Range Not Satisfiable
    33. 417 Expectation Failed
    34. 426 Upgrade Required
    35. 428 Precondition Required
    36. 429 Too Many Requests
    37. 431 Request Header Fields Too Large
    38. 451 Unavailable For Legal Reasons
    39. 500 Internal Server Error
    40. 501 Not Implemented
    41. 502 Bad Gateway
    42. 503 Service Unavailable
    43. 504 Gateway Timeout
    44. 505 HTTP Version Not Supported
    45. 511 Network Authentication Required
  20. 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: object-src
    14. CSP: plugin-types
    15. CSP: referrer
    16. CSP: report-uri
    17. CSP: require-sri-for
    18. CSP: sandbox
    19. CSP: script-src
    20. CSP: style-src
    21. CSP: upgrade-insecure-requests
    22. CSP: worker-src

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