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HTTP Header
Network Error Logging
ReportingDefines a policy for reporting network errors observed by the browser.
HTTP header reference, syntax, examples, and developer usage.
What is the Network Error Logging header?
The Network Error Logging HTTP header is used to transmit metadata between a client and server as part of HTTP requests or responses.
HTTP headers define how content should be interpreted, cached, authenticated, secured, or processed by browsers and APIs.
Direction
This header may appear in both HTTP requests and responses.
Syntax
NEL: {"report_to":"default","max_age":31536000,"include_subdomains":true}Example
NEL: {"report_to":"default","max_age":31536000,"include_subdomains":true}Common use cases
- Collecting browser-reported network failures
- Monitoring connectivity or TLS issues
- Improving reliability diagnostics for websites and applications
Common mistakes
- Using the header in the wrong request or response context
- Sending invalid header values
- Incorrect header syntax
- Assuming the header automatically changes server behaviour
Practical developer insight
NEL lets browsers send reports about failed network requests, DNS problems, TLS issues, and other connectivity errors. It is mostly relevant for observability and large-scale reliability monitoring rather than day-to-day frontend logic.