Tamper Data

License / Price: Freeware
Version: 10.1.1
Language: English
Developer: Adam Judson
OS: Windows/Unix/Mac
1 Star2 Stars3 Stars4 Stars5 Stars (10 votes, average: 3.20 out of 5)

Tamper Data is an add-on for Firefox that lets you view and modify HTTP requests before they are sent.

It shows what information the web browser is sending on your behalf, such as cookies and hidden form fields. Use of this plugin can reveal web applications that trust the client not to misbehave.


Make sure you have read the warnings.

Press the start/stop tamper to toggle tampering.

For each request (images etc. are currently filtered out) you should see a pop up prompting you to

  • tamper – trigger the tamper pop up
  • submit – do nothing


  • abort – cancel the request entirely

When you select tamper you will see the tamper window. Modify the data here. Use the context menu to make common changes.

Select OK to submit the modified values, cancel to submit the original data.

Security and Privacy

All data in request headers and body is recorded.
Be aware of this when surfing to sites that request passwords etc.
e.g. it may not be a good idea to leave this extension running while performing online banking.


As this tool modifies values in the request other tools such as live http headers (which the complicated parts of this code are based on) may not work correctly at the same time as tamperdata.

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