diff --git a/keyserver/src/fetchers/link-fetchers.js b/keyserver/src/fetchers/link-fetchers.js
--- a/keyserver/src/fetchers/link-fetchers.js
+++ b/keyserver/src/fetchers/link-fetchers.js
@@ -51,7 +51,8 @@
     threadID,
     threadRole,
   } = result[0];
-  const communityStatus = communityRole > 0 ? 'already_joined' : 'valid';
+  const communityStatus: 'already_joined' | 'valid' =
+    communityRole > 0 ? 'already_joined' : 'valid';
   const communityResult = {
     status: communityStatus,
     community: {
diff --git a/keyserver/src/fetchers/message-fetchers.js b/keyserver/src/fetchers/message-fetchers.js
--- a/keyserver/src/fetchers/message-fetchers.js
+++ b/keyserver/src/fetchers/message-fetchers.js
@@ -538,7 +538,7 @@
   const messages = parseMessageSQLResult(result, derivedMessages, viewer);
 
   const rawMessageInfos = [];
-  let currentThreadID = null;
+  let currentThreadID: ?string = null;
   let numMessagesForCurrentThreadID = 0;
   for (const message of messages) {
     const { rawMessageInfo } = message;
diff --git a/keyserver/src/fetchers/thread-permission-fetchers.js b/keyserver/src/fetchers/thread-permission-fetchers.js
--- a/keyserver/src/fetchers/thread-permission-fetchers.js
+++ b/keyserver/src/fetchers/thread-permission-fetchers.js
@@ -118,7 +118,7 @@
   return positiveRoles.length > 0;
 }
 
-type Check =
+export type Check =
   | { +check: 'is_member' }
   | { +check: 'permission', +permission: ThreadPermission };
 
@@ -400,7 +400,7 @@
   const fetchMembersPromise = fetchKnownUserInfos(viewer, allCandidates);
 
   const parentPermissionsPromise = (async () => {
-    const parentPermissions = {};
+    const parentPermissions: { [string]: ThreadPermissionsBlob } = {};
     if (!params.parentThreadID || allCandidates.length === 0) {
       return parentPermissions;
     }
diff --git a/keyserver/src/push/rescind.js b/keyserver/src/push/rescind.js
--- a/keyserver/src/push/rescind.js
+++ b/keyserver/src/push/rescind.js
@@ -122,7 +122,9 @@
   const deliveryPromises: {
     [string]: Promise<APNPushResult> | Promise<FCMPushResult>,
   } = {};
-  const notifInfo = {};
+  const notifInfo: {
+    [string]: { userID: string, threadID: string, messageID: string },
+  } = {};
   const rescindedIDs = [];
 
   for (const row of fetchResult) {
diff --git a/keyserver/src/responders/entry-responders.js b/keyserver/src/responders/entry-responders.js
--- a/keyserver/src/responders/entry-responders.js
+++ b/keyserver/src/responders/entry-responders.js
@@ -68,7 +68,7 @@
       filters: input.filters,
     };
   }
-  const filters = [];
+  const filters: Array<CalendarFilter> = [];
   if (!input.includeDeleted) {
     filters.push({ type: calendarThreadFilterTypes.NOT_DELETED });
   }
diff --git a/keyserver/src/responders/redux-state-responders.js b/keyserver/src/responders/redux-state-responders.js
--- a/keyserver/src/responders/redux-state-responders.js
+++ b/keyserver/src/responders/redux-state-responders.js
@@ -25,7 +25,10 @@
 import type { ServerWebInitialReduxStateResponse } from 'lib/types/redux-types.js';
 import { threadPermissions } from 'lib/types/thread-permission-types.js';
 import { threadTypes } from 'lib/types/thread-types-enum.js';
-import { type GlobalAccountUserInfo } from 'lib/types/user-types.js';
+import {
+  type GlobalAccountUserInfo,
+  type UserInfos,
+} from 'lib/types/user-types.js';
 import { currentDateInTimeZone } from 'lib/utils/date-utils.js';
 import { ServerError } from 'lib/utils/errors.js';
 import { promiseAll } from 'lib/utils/promises.js';
@@ -221,7 +224,7 @@
     }
     return await entryStorePromise;
   })();
-  const userInfosPromise = (async () => {
+  const userInfosPromise = (async (): Promise<UserInfos> => {
     const [userInfos, hasNotAcknowledgedPolicies] = await Promise.all([
       userInfoPromise,
       hasNotAcknowledgedPoliciesPromise,
diff --git a/keyserver/src/updaters/relationship-updaters.js b/keyserver/src/updaters/relationship-updaters.js
--- a/keyserver/src/updaters/relationship-updaters.js
+++ b/keyserver/src/updaters/relationship-updaters.js
@@ -397,7 +397,7 @@
   viewer: Viewer,
   request: RelationshipRequest,
   userIDs: $ReadOnlyArray<string>,
-) {
+): Promise<{ +[string]: string }> {
   // If you add another RelationshipAction to the supported list below, you'll
   // probably want to add it to the FRIEND / FARCASTER_MUTUAL special cases in
   // useUpdateRelationships as well
diff --git a/keyserver/src/updaters/thread-updaters.js b/keyserver/src/updaters/thread-updaters.js
--- a/keyserver/src/updaters/thread-updaters.js
+++ b/keyserver/src/updaters/thread-updaters.js
@@ -56,6 +56,7 @@
   rawThreadInfosFromServerThreadInfos,
   determineThreadAncestryForPossibleMemberResolution,
 } from '../fetchers/thread-fetchers.js';
+import { type Check } from '../fetchers/thread-permission-fetchers.js';
 import {
   checkThreadPermission,
   viewerHasPositiveRole,
@@ -420,7 +421,7 @@
     if (ignorePermissions) {
       return;
     }
-    const checks = [];
+    const checks: Array<Check> = [];
     if (sqlUpdate.name !== undefined) {
       checks.push({
         check: 'permission',
diff --git a/lib/push/utils.js b/lib/push/utils.js
--- a/lib/push/utils.js
+++ b/lib/push/utils.js
@@ -125,7 +125,8 @@
         const { type } = messageInfo;
         const { getMessageNotifyType } = messageSpecs[type];
 
-        let messageNotifyType = messageNotifyTypes.SET_UNREAD;
+        let messageNotifyType: MessageNotifyType =
+          messageNotifyTypes.SET_UNREAD;
         if (messageInfo.creatorID === userID) {
           // We don't need to notify the message author about their message
           messageNotifyType = messageNotifyTypes.NONE;
diff --git a/lib/shared/dm-ops/process-dm-ops.js b/lib/shared/dm-ops/process-dm-ops.js
--- a/lib/shared/dm-ops/process-dm-ops.js
+++ b/lib/shared/dm-ops/process-dm-ops.js
@@ -461,7 +461,8 @@
           invariant(id, 'Thick thread RawMessageInfos should always have ID');
           const { getMessageNotifyType } = messageSpecs[type];
 
-          let messageNotifyType = messageNotifyTypes.SET_UNREAD;
+          let messageNotifyType: MessageNotifyType =
+            messageNotifyTypes.SET_UNREAD;
           if (getMessageNotifyType) {
             messageNotifyType = await getMessageNotifyType(rawMessageInfo, {
               notifTargetUserID: viewerID,
diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -1070,7 +1070,7 @@
 
 const disabledPermissions: ThreadPermissionsInfo =
   permissionsDisabledByBlockArray.reduce(
-    (permissions: ThreadPermissionsInfo, permission: string) => ({
+    (permissions: ThreadPermissionsInfo, permission: ThreadPermission) => ({
       ...permissions,
       [permission]: { value: false, source: null },
     }),
diff --git a/lib/types/message-types.js b/lib/types/message-types.js
--- a/lib/types/message-types.js
+++ b/lib/types/message-types.js
@@ -158,7 +158,7 @@
   thickIDRegExp,
 } from '../utils/validation-utils.js';
 
-const composableMessageTypes = new Set([
+const composableMessageTypes = new Set<MessageType>([
   messageTypes.TEXT,
   messageTypes.IMAGES,
   messageTypes.MULTIMEDIA,
@@ -200,7 +200,7 @@
   return messageData.localID;
 }
 
-const mediaMessageTypes = new Set([
+const mediaMessageTypes = new Set<MessageType>([
   messageTypes.IMAGES,
   messageTypes.MULTIMEDIA,
 ]);
diff --git a/lib/utils/validation-utils.test.js b/lib/utils/validation-utils.test.js
--- a/lib/utils/validation-utils.test.js
+++ b/lib/utils/validation-utils.test.js
@@ -15,7 +15,7 @@
 describe('Validation utils', () => {
   describe('tNumEnum validator', () => {
     it('Should discard when accepted set is empty', () => {
-      expect(tNumEnum([]).is(1)).toBe(false);
+      expect(tNumEnum(([]: Array<number>)).is(1)).toBe(false);
     });
 
     it('Should accept when array contains number', () => {
diff --git a/native/roles/community-roles-screen.react.js b/native/roles/community-roles-screen.react.js
--- a/native/roles/community-roles-screen.react.js
+++ b/native/roles/community-roles-screen.react.js
@@ -11,6 +11,7 @@
   useRoleUserSurfacedPermissions,
 } from 'lib/shared/thread-utils.js';
 import type { ThreadInfo } from 'lib/types/minimally-encoded-thread-permissions-types.js';
+import type { UserSurfacedPermission } from 'lib/types/thread-permission-types';
 
 import RolePanelEntry from './role-panel-entry.react.js';
 import type { RolesNavigationProp } from './roles-navigator.react.js';
@@ -89,7 +90,7 @@
         threadInfo,
         action: 'create_role',
         roleName: 'New role',
-        rolePermissions: new Set(),
+        rolePermissions: new Set<UserSurfacedPermission>(),
       }),
     [threadInfo, props.navigation],
   );
diff --git a/web/url-utils.js b/web/url-utils.js
--- a/web/url-utils.js
+++ b/web/url-utils.js
@@ -135,7 +135,8 @@
 
   if (urlInfo.selectedUserList) {
     const selectedUsers = _keyBy('id')(navInfo?.selectedUserList ?? []);
-    const userInfos = backupInfo.userInfos ?? {};
+    const userInfos: { +[id: string]: AccountUserInfo } =
+      backupInfo.userInfos ?? {};
     newNavInfo.selectedUserList = urlInfo.selectedUserList
       ?.map(id => selectedUsers[id] ?? userInfos[id])
       ?.filter(Boolean);