Extracted from the Android app (v18.18.38), this includes all possible fields that clients might use, as well as debugging fields that aren't used at all.

innertube-full-context.json

{
   "context":{
      "client":{
         "hl":"",
         "gl":"",
         "remoteHost":"1.2.3.4",
         "deviceId":"",
         "debugDeviceIdOverride":"",
         "experimentIds":[
            
         ],
         "carrierGeo":"",
         "crackedHl":false,
         "deviceMake":"Google",
         "deviceModel":"sdk_gphone64_x86_64",
         "visitorData":"CgtEeXp4V2c4aThfQSi5m6mzBjIKCgJCUhIEGgAgUToKIPDc49TU4J6EZg%3D%3D",
         "userAgent":"com.google.android.youtube/18.18.38(Linux; U; Android 14; en_US; sdk_gphone64_x86_64 Build/UPB4.230623.005) gzip,gzip(gfe)",
         "clientName":"ANDROID",
         "clientVersion":"18.18.38",
         "osName":"Android",
         "osVersion":"14",
         "projectId":"",
         "acceptLanguage":"en-US",
         "acceptRegion":"US",
         "originalUrl":"",
         "rawDeviceId":"",
         "configData":"",
         "clientScreen":"UNKNOWN",
         "mwebUi":"UNKNOWN_MWEB_UI",
         "theme":"UNKNOWN_THEME",
         "spacecastToken":"",
         "internalGeo":"",
         "applicationState":"UNKNOWN_APPLICATION_STATE",
         "playerType":"UNKNOWN_PLAYER",
         "screenWidthPoints":432,
         "screenHeightPoints":840,
         "screenWidthInches":2.7,
         "screenHeightInches":5.25,
         "screenPixelDensity":3,
         "platform":"UNKNOWN_PLATFORM",
         "clientFormFactor":"SMALL_FORM_FACTOR",
         "forwardedFor":"",
         "mobileDataPlanInfo":{
            "cpid":"",
            "serializedDataPlanStatus":[
               
            ],
            "carrierId":"0",
            "dataSavingQualityPickerEnabled":false,
            "mccmnc":""
         },
         "gmscoreVersionCode":231818047,
         "webpSupport":false,
         "cameraType":"CAMERA_FRONT_AND_BACK",
         "experimentsToken":"",
         "windowWidthPoints":432,
         "windowHeightPoints":840,
         "connectionType":"CONN_WIFI_METERED",
         "configInfo":{
            "coldConfigData":"SomeLongBase64",
            "coldHashData":"SomeLongBase64",
            "appInstallData":"SomeLongBase64"
         },
         "androidSdkVersion":34,
         "screenDensityFloat":2.5,
         "firstTimeSignInExperimentIds":[
            
         ],
         "utcOffsetMinutes":-180,
         "animatedWebpSupport":false,
         "internalGeoIp":"",
         "contentSizeCategory":"",
         "fontScale":0,
         "userInterfaceTheme":"USER_INTERFACE_THEME_LIGHT",
         "timeZone":"America/Sao_Paulo",
         "emlTemplateContext":"SomeLongBase64",
         "coldAppBundleConfigData":"",
         "heterodyneIds":[
            {
               "clearBlob":"",
               "encryptedBlob":[
                  "CAMSAA==",
                  "CAMSCBUBnuS2EP4G",
                  "CAMSBhUDo7DXEw==",
                  "CAMSBhUDlOK2EA=="
               ],
               "usersMatch":false,
               "clearBlobJs":""
            }
         ],
         "browserName":"",
         "browserVersion":"",
         "locationPlayabilityToken":"",
         "platformDetail":"PLATFORM_DETAIL_UNKNOWN",
         "releaseYear":0,
         "chipset":"AOSP;ranchu",
         "firmwareVersion":"",
         "effectiveConnectionType":"EFFECTIVE_CONNECTION_TYPE_4G",
         "memoryTotalKbytes":"4452312",
         "notificationPermissionInfo":{
            "notificationsSetting":"NOTIFICATIONS_SETTING_ENABLED",
            "lastDeviceOptInChangeTimeAgoSec":"6413274"
         },
         "deviceBrand":"google",
         "srsDatapushBuildIds":[
            {
               "datapushBuild":{
                  "buildId":"1778",
                  "clientExperimentId":0,
                  "accessType":"ACCESS_TYPE_EMBEDDED"
               }
            }
         ],
         "playerDatapushBuildIds":[
            
         ],
         "glDeviceInfo":{
            "glRenderer":"Unknown Renderer",
            "glEsVersionMajor":3,
            "glEsVersionMinor":1
         },
         "acceptHeader":"",
         "deviceExperimentId":"",
         "encodedHacks":"0"
      },
      "user":{
         "onBehalfOfUser":"",
         "safetyMode":"SAFETY_MODE_NONE",
         "enableSafetyMode":false,
         "credentialTransferTokens":[
            
         ],
         "isIncognito":false,
         "lockedSafetyMode":false,
         "serializedDelegationContext":""
      },
      "request":{
         "thirdPartyDigest":"",
         "useSsl":false,
         "returnErrorDetail":false,
         "ifNoneMatch":"",
         "returnLogEntry":false,
         "isPrefetch":false,
         "internalExperimentFlags":[
            
         ],
         "returnDebugData":false,
         "innertubez":"",
         "mdxEnvironment":"UNKNOWN",
         "mdxControlMode":"MDX_CONTROL_MODE_UNKNOWN",
         "traceProto":false,
         "returnLogEntryJson":false,
         "sherlogUsername":"",
         "consistencyTokenJars":[
            {
               "encryptedTokenJarContents":"SomeLongBase64",
               "expirationSeconds":"600"
            }
         ],
         "returnLogEntryProto":false,
         "externalPrequestContext":"",
         "innertubeTokenJar":{
            "appTokens":[
               
            ],
            "userTokens":[
               {
                  "type":5,
                  "value":"KgsIv8yw5LrXhgMQAQ==",
                  "maxAgeSeconds":410139,
                  "clearTokens":false,
                  "creationTimeUsec":"1718243218978884"
               }
            ]
         },
         "eats":""
      },
      "clickTracking":{
         "clickTrackingParams":"SomeLongBase64"
      },
      "adSignalsInfo":{
         "params":[
            {
               "key":"ms",
               "value":"SomeLongBase64",
               "intValue":0,
               "boolValue":false,
               "floatValue":0
            }
         ],
         "bid":"",
         "mutsuId":"",
         "consentBumpState":"",
         "atTrackingManagerAuthorizationStatus":"AT_TRACKING_MANAGER_AUTHORIZATION_STATUS_UNKNOWN",
         "advertisingId":"7520abc8-0aff-410f-916b-a54829e826ca",
         "advertisingIdSignalType":"DEVICE_ID_TYPE_ANDROID_AD_ID",
         "limitAdTracking":false,
         "attributionOsSupportedVersion":""
      },
      "clientScreenNonce":"",
      "activePlayers":[
      ]
   }
}