Last-Modified - HTTP | MDN

archived 12 Jul 2018 20:54:52 UTC
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The Last-Modified response HTTP header contains the date and time at which the origin server believes the resource was last modified. It is used as a validator to determine if a resource received or stored is the same. Less accurate than an ETag header, it is a fallback mechanism. Conditional requests containing If-Modified-Since or If-Unmodified-Since headers make use of this field.
Header type Response header
Forbidden header name no
CORS-safelisted response-header yes

Syntax

Last-Modified: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT

Directives

<day-name>
One of "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", or "Sun" (case-sensitive).
<day>
2 digit day number, e.g. "04" or "23".
<month>
One of "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" (case sensitive).
<year>
4 digit year number, e.g. "1990" or "2016".
<hour>
2 digit hour number, e.g. "09" or "23".
<minute>
2 digit minute number, e.g. "04" or "59".
<second>
2 digit second number, e.g. "04" or "59".
GMT
Greenwich Mean Time. HTTP dates are always expressed in GMT, never in local time.

Examples

Last-Modified: Wed, 21 Oct 2015 07:28:00 GMT

Specifications

Specification Title
RFC 7232, section 2.2: Last-Modified Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests

Browser compatibility

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
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support Yes Yes Yes Yes Yes Yes Yes
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic support
ExperimentalDeprecatedNon-standard
 Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes Full support Yes

Legend

Full support  
Full support
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.
Deprecated. Not for use in new websites.
Deprecated. Not for use in new websites.

See also

Document Tags and Contributors

Contributors to this page: gamemaster7riesen, WayneCui, fscholz, teoli
Last updated by: gamemaster7riesen,
Related Topics
  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. Expect-CT
    35. Expires
    36. Forwarded
    37. From
    38. Host
    39. If-Match
    40. If-Modified-Since
    41. If-None-Match
    42. If-Range
    43. If-Unmodified-Since
    44. Keep-Alive
    45. Large-Allocation
    46. Last-Modified
    47. Location
    48. Origin
    49. Pragma
    50. Proxy-Authenticate
    51. Proxy-Authorization
    52. Public-Key-Pins
    53. Public-Key-Pins-Report-Only
    54. Range
    55. Referer
    56. Referrer-Policy
    57. Retry-After
    58. Server
    59. Set-Cookie
    60. Set-Cookie2
    61. SourceMap
    62. Strict-Transport-Security
    63. TE
    64. Timing-Allow-Origin
    65. Tk
    66. Trailer
    67. Transfer-Encoding
    68. Upgrade-Insecure-Requests
    69. User-Agent
    70. Vary
    71. Via
    72. WWW-Authenticate
    73. Warning
    74. X-Content-Type-Options
    75. X-DNS-Prefetch-Control
    76. X-Forwarded-For
    77. X-Forwarded-Host
    78. X-Forwarded-Proto
    79. X-Frame-Options
    80. X-XSS-Protection
  18. HTTP request methods
    1. CONNECT
    2. DELETE
    3. GET
    4. HEAD
    5. OPTIONS
    6. PATCH
    7. POST
    8. PUT
    9. TRACE
  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. 418 I'm a teapot
    35. 426 Upgrade Required
    36. 428 Precondition Required
    37. 429 Too Many Requests
    38. 431 Request Header Fields Too Large
    39. 451 Unavailable For Legal Reasons
    40. 500 Internal Server Error
    41. 501 Not Implemented
    42. 502 Bad Gateway
    43. 503 Service Unavailable
    44. 504 Gateway Timeout
    45. 505 HTTP Version Not Supported
    46. 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
    23. report-to

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