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All of these are devtools_network actions and need a running devtools_session on the tab. They are undone by devtools_session stop.

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Mock a response

pattern is a URL glob. response takes status, headers, contentType, and either body (string) or json. rules lists active mocks, unmock removes one by pattern. Mocks are applied through Chrome’s Fetch domain, so they also cover requests made before the page’s JavaScript runs.

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Block requests

Blocked requests fail in the page like a network error. unblock lifts them. For a policy that persists across tabs and sessions, use browser_policy instead; see Domain policies.

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Throttle

Presets: none, offline, slow3g, fast3g, 4g, or custom latencyMs, downloadKbps, uploadKbps. CPU throttling lives in devtools_emulation {action: "cpu", rate}.

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Cache

{ "action": "cache", "disabled": true } is the “Disable cache” checkbox.

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Replay

Re-issues a captured request from the page with optional changes to method, URL, headers or body, and returns the response. Handy for probing an API without touching the UI.

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Export

{ "action": "har" } writes a HAR file of everything captured to the artifacts directory. It opens in Chrome’s Network panel, Charles, Proxyman and friends.