diff --git a/keyserver/src/creators/message-creator.js b/keyserver/src/creators/message-creator.js
--- a/keyserver/src/creators/message-creator.js
+++ b/keyserver/src/creators/message-creator.js
@@ -556,15 +556,19 @@
   }
 }
 
+type LatestMessagePerThread = {
+  +latestMessage: string,
+  +latestReadMessage?: string,
+};
 function determineLatestMessagesPerThread(
   preUserPushInfo: UserThreadInfo,
   userID: string,
   threadsToMessageIndices: $ReadOnlyMap<string, $ReadOnlyArray<number>>,
   messageInfos: $ReadOnlyArray<RawMessageInfo>,
-) {
+): $ReadOnlyMap<string, LatestMessagePerThread> {
   const { threadIDs, notFocusedThreadIDs, subthreadsCanSetToUnread } =
     preUserPushInfo;
-  const latestMessagesPerThread = new Map();
+  const latestMessagesPerThread = new Map<string, LatestMessagePerThread>();
   for (const threadID of threadIDs) {
     const messageIndices = threadsToMessageIndices.get(threadID);
     invariant(messageIndices, `indices should exist for thread ${threadID}`);
diff --git a/keyserver/src/creators/report-creator.js b/keyserver/src/creators/report-creator.js
--- a/keyserver/src/creators/report-creator.js
+++ b/keyserver/src/creators/report-creator.js
@@ -192,7 +192,7 @@
   first: { +[id: string]: O },
   second: { +[id: string]: O },
 ): Set<string> {
-  const nonMatchingIDs = new Set();
+  const nonMatchingIDs = new Set<string>();
   for (const id in first) {
     if (!_isEqual(first[id])(second[id])) {
       nonMatchingIDs.add(id);
diff --git a/keyserver/src/creators/update-creator.js b/keyserver/src/creators/update-creator.js
--- a/keyserver/src/creators/update-creator.js
+++ b/keyserver/src/creators/update-creator.js
@@ -409,8 +409,10 @@
     ({ currentUser }) => currentUser,
   );
   const threadIDsNeedingFetch = viewerInfo.threadInfos
-    ? new Set()
-    : new Set(entitiesToFetch.map(({ threadID }) => threadID).filter(Boolean));
+    ? new Set<string>()
+    : new Set<string>(
+        entitiesToFetch.map(({ threadID }) => threadID).filter(Boolean),
+      );
   const entryIDsNeedingFetch = new Set(
     entitiesToFetch.map(({ entryID }) => entryID).filter(Boolean),
   );
diff --git a/keyserver/src/cron/update-geoip-db.js b/keyserver/src/cron/update-geoip-db.js
--- a/keyserver/src/cron/update-geoip-db.js
+++ b/keyserver/src/cron/update-geoip-db.js
@@ -8,8 +8,9 @@
 
 import { handleAsyncPromise } from '../responders/handlers.js';
 
+type GeoIPLicenseConfig = { +key: string };
 async function updateGeoipDB(): Promise<void> {
-  const geoipLicense = await getCommConfig({
+  const geoipLicense = await getCommConfig<GeoIPLicenseConfig>({
     folder: 'secrets',
     name: 'geoip_license',
   });
@@ -20,7 +21,7 @@
   await spawnUpdater(geoipLicense);
 }
 
-function spawnUpdater(geoipLicense: { key: string }): Promise<void> {
+function spawnUpdater(geoipLicense: GeoIPLicenseConfig): Promise<void> {
   const spawned = childProcess.spawn(process.execPath, [
     '../node_modules/geoip-lite/scripts/updatedb.js',
     `license_key=${geoipLicense.key}`,
diff --git a/keyserver/src/database/db-config.js b/keyserver/src/database/db-config.js
--- a/keyserver/src/database/db-config.js
+++ b/keyserver/src/database/db-config.js
@@ -49,7 +49,7 @@
       dbType: assertValidDBType(process.env.COMM_DATABASE_TYPE),
     };
   } else {
-    const importedDBConfig = await getCommConfig({
+    const importedDBConfig = await getCommConfig<DBConfig>({
       folder: 'secrets',
       name: 'db_config',
     });
diff --git a/keyserver/src/database/migration-config.js b/keyserver/src/database/migration-config.js
--- a/keyserver/src/database/migration-config.js
+++ b/keyserver/src/database/migration-config.js
@@ -535,7 +535,7 @@
         WHERE m1.type = ${SIDEBAR_SOURCE} AND m2.type = ${TOGGLE_PIN}
       `);
 
-      const threadIDs = new Set();
+      const threadIDs = new Set<string>();
       for (const row of result) {
         threadIDs.add(row.thread.toString());
       }
diff --git a/keyserver/src/endpoints.js b/keyserver/src/endpoints.js
--- a/keyserver/src/endpoints.js
+++ b/keyserver/src/endpoints.js
@@ -200,7 +200,10 @@
   uploadMediaMetadataInputValidator,
 } from './uploads/uploads.js';
 
-const ignoredArgumentValidator = t.irreducible('Ignored argument', () => true);
+const ignoredArgumentValidator = t.irreducible<mixed>(
+  'Ignored argument',
+  () => true,
+);
 
 const jsonEndpoints: { [id: Endpoint]: JSONResponder } = {
   create_account: createJSONResponder(
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
@@ -348,7 +348,7 @@
   const messages = await parseMessageSQLResult(result, derivedMessages, viewer);
 
   const rawMessageInfos = [];
-  const threadToMessageCount = new Map();
+  const threadToMessageCount = new Map<string, number>();
   for (const message of messages) {
     const { rawMessageInfo } = message;
     rawMessageInfos.push(rawMessageInfo);
@@ -844,7 +844,7 @@
   `;
 
   const [result] = await dbQuery(latestEditedMessageQuery);
-  const latestContentByID = new Map();
+  const latestContentByID = new Map<string, EditMessageContent>();
   for (const row of result) {
     if (!row.content) {
       continue;
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
@@ -142,8 +142,8 @@
   viewer: Viewer,
   permissionsToCheck: $ReadOnlyArray<ThreadPermission>,
   threadIDs: $ReadOnlyArray<string>,
-) {
-  const threadIDsWithDisabledPermissions = new Set();
+): Promise<$ReadOnlySet<string>> {
+  const threadIDsWithDisabledPermissions = new Set<string>();
 
   const permissionMightBeDisabled = permissionsToCheck.some(permission =>
     permissionsDisabledByBlock.has(permission),
@@ -198,6 +198,8 @@
 // It doesn't matter what value we pass in, as long as it's positive.
 const arbitraryPositiveRole = '1';
 
+type ContainingStatus = 'member' | 'non-member' | 'no-containing-thread';
+
 type CandidateMembers = {
   +[key: string]: ?$ReadOnlyArray<string>,
 };
@@ -216,7 +218,7 @@
 ): Promise<CandidateMembers> {
   const requireRelationship = options?.requireRelationship ?? true;
 
-  const allCandidatesSet = new Set();
+  const allCandidatesSet = new Set<string>();
   for (const key in candidates) {
     const candidateGroup = candidates[key];
     if (!candidateGroup) {
@@ -248,9 +250,9 @@
   })();
 
   const memberOfContainingThreadPromise: Promise<
-    Map<string, 'member' | 'non-member' | 'no-containing-thread'>,
+    Map<string, ContainingStatus>,
   > = (async () => {
-    const results = new Map();
+    const results = new Map<string, ContainingStatus>();
     if (allCandidates.length === 0) {
       return results;
     }
@@ -282,7 +284,7 @@
       memberOfContainingThreadPromise,
     ]);
 
-  const ignoreMembers = new Set();
+  const ignoreMembers = new Set<string>();
   for (const memberID of allCandidates) {
     const member = fetchedMembers[memberID];
     if (!member && requireRelationship) {
diff --git a/keyserver/src/push/providers.js b/keyserver/src/push/providers.js
--- a/keyserver/src/push/providers.js
+++ b/keyserver/src/push/providers.js
@@ -27,14 +27,26 @@
   return codeVersion && codeVersion >= 87 ? 'comm_fcm_config' : 'fcm_config';
 }
 
-const cachedAPNProviders = new Map();
+type APNConfig = {
+  +token: {
+    +key: string,
+    +keyId: string,
+    +teamId: string,
+  },
+  +production: boolean,
+};
+
+const cachedAPNProviders = new Map<APNPushProfile, ?APNProvider>();
 async function getAPNProvider(profile: APNPushProfile): Promise<?APNProvider> {
   const provider = cachedAPNProviders.get(profile);
   if (provider !== undefined) {
     return provider;
   }
   try {
-    const apnConfig = await getCommConfig({ folder: 'secrets', name: profile });
+    const apnConfig = await getCommConfig<APNConfig>({
+      folder: 'secrets',
+      name: profile,
+    });
     invariant(apnConfig, `APN config missing for ${profile}`);
     if (!cachedAPNProviders.has(profile)) {
       cachedAPNProviders.set(profile, new apn.Provider(apnConfig));
@@ -47,14 +59,30 @@
   return cachedAPNProviders.get(profile);
 }
 
-const cachedFCMProviders = new Map();
+type FCMConfig = {
+  +type: string,
+  +project_id: string,
+  +private_key_id: string,
+  +private_key: string,
+  +client_email: string,
+  +client_id: string,
+  +auth_uri: string,
+  +token_uri: string,
+  +auth_provider_x509_cert_url: string,
+  +client_x509_cert_url: string,
+};
+
+const cachedFCMProviders = new Map<FCMPushProfile, ?FirebaseApp>();
 async function getFCMProvider(profile: FCMPushProfile): Promise<?FirebaseApp> {
   const provider = cachedFCMProviders.get(profile);
   if (provider !== undefined) {
     return provider;
   }
   try {
-    const fcmConfig = await getCommConfig({ folder: 'secrets', name: profile });
+    const fcmConfig = await getCommConfig<FCMConfig>({
+      folder: 'secrets',
+      name: profile,
+    });
     invariant(fcmConfig, `FCM config missed for ${profile}`);
     if (!cachedFCMProviders.has(profile)) {
       cachedFCMProviders.set(
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
@@ -72,7 +72,7 @@
   fetchQuery.append(SQL` GROUP BY n.id, m.user`);
   const [fetchResult] = await dbQuery(fetchQuery);
 
-  const allDeviceTokens = new Set();
+  const allDeviceTokens = new Set<string>();
   const parsedDeliveries: { [string]: $ReadOnlyArray<ParsedDelivery> } = {};
 
   for (const row of fetchResult) {
diff --git a/keyserver/src/push/send.js b/keyserver/src/push/send.js
--- a/keyserver/src/push/send.js
+++ b/keyserver/src/push/send.js
@@ -659,8 +659,8 @@
 async function fetchInfos(pushInfo: PushInfo) {
   const usersToCollapsableNotifInfo = await fetchCollapsableNotifs(pushInfo);
 
-  const threadIDs = new Set();
-  const threadWithChangedNamesToMessages = new Map();
+  const threadIDs = new Set<string>();
+  const threadWithChangedNamesToMessages = new Map<string, Array<string>>();
   const addThreadIDsFromMessageInfos = (rawMessageInfo: RawMessageInfo) => {
     const threadID = rawMessageInfo.threadID;
     threadIDs.add(threadID);
@@ -756,7 +756,7 @@
   serverThreadInfos: { +[threadID: string]: ServerThreadInfo },
   usersToCollapsableNotifInfo: { +[userID: string]: CollapsableNotifInfo[] },
 ) {
-  const missingUserIDs = new Set();
+  const missingUserIDs = new Set<string>();
 
   for (const threadID in serverThreadInfos) {
     const serverThreadInfo = serverThreadInfos[threadID];
@@ -815,11 +815,14 @@
 function getDevicesByPlatform(
   devices: $ReadOnlyArray<Device>,
 ): Map<Platform, Map<string, Array<NotificationTargetDevice>>> {
-  const byPlatform = new Map();
+  const byPlatform = new Map<
+    Platform,
+    Map<string, Array<NotificationTargetDevice>>,
+  >();
   for (const device of devices) {
     let innerMap = byPlatform.get(device.platform);
     if (!innerMap) {
-      innerMap = new Map();
+      innerMap = new Map<string, Array<NotificationTargetDevice>>();
       byPlatform.set(device.platform, innerMap);
     }
     const codeVersion: number =
@@ -1520,7 +1523,7 @@
   selectQuery.append(sqlCondition);
   const [result] = await dbQuery(selectQuery);
 
-  const userCookiePairsToInvalidDeviceTokens = new Map();
+  const userCookiePairsToInvalidDeviceTokens = new Map<string, Set<string>>();
   for (const row of result) {
     const userCookiePair = `${row.user}|${row.id}`;
     const existing = userCookiePairsToInvalidDeviceTokens.get(userCookiePair);
diff --git a/keyserver/src/responders/comm-landing-responders.js b/keyserver/src/responders/comm-landing-responders.js
--- a/keyserver/src/responders/comm-landing-responders.js
+++ b/keyserver/src/responders/comm-landing-responders.js
@@ -9,7 +9,7 @@
 import { sendEmailSubscriptionRequestToAshoat } from '../emails/subscribe-email-updates.js';
 import { checkInputValidator } from '../utils/validation-utils.js';
 
-const emailSubscriptionInputValidator = tShape({
+const emailSubscriptionInputValidator = tShape<EmailSubscriptionRequest>({
   email: tEmail,
 });
 
diff --git a/keyserver/src/responders/user-responders.js b/keyserver/src/responders/user-responders.js
--- a/keyserver/src/responders/user-responders.js
+++ b/keyserver/src/responders/user-responders.js
@@ -3,7 +3,7 @@
 import type { Utility as OlmUtility } from '@commapp/olm';
 import invariant from 'invariant';
 import { ErrorTypes, SiweMessage } from 'siwe';
-import t, { type TInterface, type TUnion } from 'tcomb';
+import t, { type TInterface, type TUnion, type TEnums } from 'tcomb';
 import bcrypt from 'twin-bcrypt';
 
 import {
@@ -40,6 +40,7 @@
   IdentityKeysBlob,
   SignedIdentityKeysBlob,
 } from 'lib/types/crypto-types.js';
+import type { DeviceType } from 'lib/types/device-types';
 import {
   type CalendarQuery,
   rawEntryInfoValidator,
@@ -221,10 +222,15 @@
   return result;
 }
 
-const deviceTokenUpdateRequestInputValidator = tShape({
-  deviceType: t.maybe(t.enums.of(['ios', 'android'])),
-  deviceToken: t.String,
-});
+type OldDeviceTokenUpdateRequest = {
+  +deviceType?: ?DeviceType,
+  +deviceToken: string,
+};
+const deviceTokenUpdateRequestInputValidator =
+  tShape<OldDeviceTokenUpdateRequest>({
+    deviceType: t.maybe(t.enums.of(['ios', 'android'])),
+    deviceToken: t.String,
+  });
 
 export const registerRequestInputValidator: TInterface<RegisterRequest> =
   tShape<RegisterRequest>({
@@ -434,7 +440,7 @@
       threadInfos: t.dict(tID, rawThreadInfoValidator),
       userInfos: t.list(userInfoValidator),
     }),
-    notAcknowledgedPolicies: t.maybe(t.list(policyTypeValidator)),
+    notAcknowledgedPolicies: t.maybe(t.list<TEnums>(policyTypeValidator)),
   });
 
 async function logInResponder(
diff --git a/keyserver/src/scripts/merge-users.js b/keyserver/src/scripts/merge-users.js
--- a/keyserver/src/scripts/merge-users.js
+++ b/keyserver/src/scripts/merge-users.js
@@ -49,8 +49,8 @@
     ({ sql: updateUserRowQuery, updateDatas } = replaceUserResult);
   }
 
-  const usersGettingUpdate = new Set();
-  const usersNeedingUpdate = new Set();
+  const usersGettingUpdate = new Set<string>();
+  const usersNeedingUpdate = new Set<string>();
   const needUserInfoUpdate = replaceUserInfo && replaceUserInfo.username;
   const setGettingUpdate = (threadInfo: ServerThreadInfo) => {
     if (!needUserInfoUpdate) {
diff --git a/keyserver/src/scripts/validate-role-permissions.js b/keyserver/src/scripts/validate-role-permissions.js
--- a/keyserver/src/scripts/validate-role-permissions.js
+++ b/keyserver/src/scripts/validate-role-permissions.js
@@ -8,6 +8,7 @@
 import {
   configurableCommunityPermissions,
   userSurfacedPermissions,
+  type UserSurfacedPermission,
 } from 'lib/types/thread-permission-types.js';
 import { threadTypes } from 'lib/types/thread-types-enum.js';
 import { deepDiff, values } from 'lib/utils/objects.js';
@@ -106,8 +107,10 @@
     // discrepancies that could be linked to a specific user-surfaced
     // permission. This could be useful in manually parsing through the
     // script results to 'write off' discrepancies as user role edits.
-    const userSurfacedExpectedPermissionsToExistingPermissions = new Set();
-    const userSurfacedExistingPermissionsToExpectedPermissions = new Set();
+    const userSurfacedExpectedPermissionsToExistingPermissions =
+      new Set<UserSurfacedPermission>();
+    const userSurfacedExistingPermissionsToExpectedPermissions =
+      new Set<UserSurfacedPermission>();
 
     for (const permission of values(userSurfacedPermissions)) {
       const permissionSet = Array.from(
diff --git a/keyserver/src/socket/session-utils.js b/keyserver/src/socket/session-utils.js
--- a/keyserver/src/socket/session-utils.js
+++ b/keyserver/src/socket/session-utils.js
@@ -423,7 +423,7 @@
   const idsToFetch = Object.fromEntries(
     values(serverStateSyncSpecs)
       .filter(spec => spec.innerHashSpec?.hashKey)
-      .map(spec => [spec.innerHashSpec?.hashKey, new Set()]),
+      .map(spec => [spec.innerHashSpec?.hashKey, new Set<string>()]),
   );
   for (const key of invalidKeys) {
     const [innerHashKey, id] = key.split('|');
diff --git a/keyserver/src/socket/socket.js b/keyserver/src/socket/socket.js
--- a/keyserver/src/socket/socket.js
+++ b/keyserver/src/socket/socket.js
@@ -94,7 +94,7 @@
 } from '../utils/validation-utils.js';
 
 const clientSocketMessageInputValidator: TUnion<ClientSocketMessage> = t.union([
-  tShape({
+  tShape<InitialClientSocketMessage>({
     type: t.irreducible(
       'clientSocketMessageTypes.INITIAL',
       x => x === clientSocketMessageTypes.INITIAL,
@@ -114,7 +114,7 @@
       clientResponses: t.list(clientResponseInputValidator),
     }),
   }),
-  tShape({
+  tShape<ResponsesClientSocketMessage>({
     type: t.irreducible(
       'clientSocketMessageTypes.RESPONSES',
       x => x === clientSocketMessageTypes.RESPONSES,
@@ -124,14 +124,14 @@
       clientResponses: t.list(clientResponseInputValidator),
     }),
   }),
-  tShape({
+  tShape<PingClientSocketMessage>({
     type: t.irreducible(
       'clientSocketMessageTypes.PING',
       x => x === clientSocketMessageTypes.PING,
     ),
     id: t.Number,
   }),
-  tShape({
+  tShape<AckUpdatesClientSocketMessage>({
     type: t.irreducible(
       'clientSocketMessageTypes.ACK_UPDATES',
       x => x === clientSocketMessageTypes.ACK_UPDATES,
@@ -141,7 +141,7 @@
       currentAsOf: t.Number,
     }),
   }),
-  tShape({
+  tShape<APIRequestClientSocketMessage>({
     type: t.irreducible(
       'clientSocketMessageTypes.API_REQUEST',
       x => x === clientSocketMessageTypes.API_REQUEST,
diff --git a/keyserver/src/updaters/activity-updaters.js b/keyserver/src/updaters/activity-updaters.js
--- a/keyserver/src/updaters/activity-updaters.js
+++ b/keyserver/src/updaters/activity-updaters.js
@@ -6,6 +6,7 @@
 
 import { localIDPrefix } from 'lib/shared/message-utils.js';
 import type {
+  ActivityUpdate,
   UpdateActivityResult,
   UpdateActivityRequest,
   SetThreadUnreadStatusRequest,
@@ -58,7 +59,7 @@
     throw new ServerError('not_logged_in');
   }
 
-  const focusUpdatesByThreadID = new Map();
+  const focusUpdatesByThreadID = new Map<string, Array<ActivityUpdate>>();
   for (const activityUpdate of request.updates) {
     const threadID = activityUpdate.threadID;
     const updatesForThreadID = focusUpdatesByThreadID.get(threadID) ?? [];
@@ -87,7 +88,7 @@
     return { unfocusedToUnread: [] };
   }
 
-  const memberThreadIDs = new Set();
+  const memberThreadIDs = new Set<string>();
   const verifiedThreadIDs = [];
   for (const threadData of verifiedThreadsData) {
     if (threadData.role > 0) {
@@ -317,7 +318,7 @@
   `;
   const [result] = await dbQuery(query);
 
-  const threadsWithNewerMessages = new Set();
+  const threadsWithNewerMessages = new Set<string>();
   for (const row of result) {
     const threadID = row.thread.toString();
     const serverLatestMessage = row.latest_message;
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
@@ -281,7 +281,7 @@
   selectQuery.append(mergeOrConditions(conditions));
 
   const [result] = await dbQuery(selectQuery);
-  const existingStatuses = new Map();
+  const existingStatuses = new Map<string, number>();
   for (const row of result) {
     existingStatuses.set(`${row.user1}|${row.user2}`, row.status);
   }
diff --git a/keyserver/src/updaters/thread-permission-updaters.js b/keyserver/src/updaters/thread-permission-updaters.js
--- a/keyserver/src/updaters/thread-permission-updaters.js
+++ b/keyserver/src/updaters/thread-permission-updaters.js
@@ -86,6 +86,11 @@
   permissionsFromParent?: ?ThreadPermissionsBlob,
   memberOfContainingThread?: boolean,
 };
+type ExistingMembership = {
+  +oldRole: string,
+  +oldPermissions: ?ThreadPermissionsBlob,
+  +oldPermissionsForChildren: ?ThreadPermissionsBlob,
+};
 async function changeRole(
   threadID: string,
   userIDs: $ReadOnlyArray<string>,
@@ -156,7 +161,7 @@
     depth,
   } = roleThreadResult;
 
-  const existingMembershipInfo = new Map();
+  const existingMembershipInfo = new Map<string, ExistingMembership>();
   for (const row of membershipResults) {
     const userID = row.user.toString();
     existingMembershipInfo.set(userID, {
@@ -202,7 +207,7 @@
   }
 
   const membershipRows: Array<MembershipRow> = [];
-  const toUpdateDescendants = new Map();
+  const toUpdateDescendants = new Map<string, AncestorChanges>();
   for (const userID of userIDs) {
     const existingMembership = existingMembershipInfo.get(userID);
     const oldRole = existingMembership?.oldRole ?? '-1';
@@ -451,7 +456,7 @@
         relationshipChangeset.setAllRelationshipsExist(existingMemberIDs);
       }
 
-      const usersForNextLayer = new Map();
+      const usersForNextLayer = new Map<string, AncestorChanges>();
       for (const [userID, user] of users) {
         const {
           curRolePermissions,
@@ -809,7 +814,7 @@
   }
 
   const membershipRows: Array<MembershipRow> = [];
-  const toUpdateDescendants = new Map();
+  const toUpdateDescendants = new Map<string, AncestorChanges>();
   for (const [userID, membership] of membershipInfo) {
     const { rolePermissions: intendedRolePermissions, permissionsFromParent } =
       membership;
@@ -1110,7 +1115,7 @@
   }
   const { membershipRows, relationshipChangeset } = changeset;
 
-  const membershipRowMap = new Map();
+  const membershipRowMap = new Map<string, MembershipRow>();
   for (const row of membershipRows) {
     const { userID, threadID } = row;
     changedThreadIDs.add(threadID);
@@ -1144,7 +1149,7 @@
     }
   }
 
-  const threadsToSavedUsers = new Map();
+  const threadsToSavedUsers = new Map<string, Array<string>>();
   for (const row of membershipRowMap.values()) {
     const { userID, threadID } = row;
     let savedUsers = threadsToSavedUsers.get(threadID);
diff --git a/keyserver/src/utils/ens-cache.js b/keyserver/src/utils/ens-cache.js
--- a/keyserver/src/utils/ens-cache.js
+++ b/keyserver/src/utils/ens-cache.js
@@ -9,9 +9,11 @@
   type GetENSNames,
 } from 'lib/utils/ens-helpers.js';
 
+type AlchemyConfig = { +key: string };
+
 let getENSNames: ?GetENSNames;
 async function initENSCache() {
-  const alchemySecret = await getCommConfig({
+  const alchemySecret = await getCommConfig<AlchemyConfig>({
     folder: 'secrets',
     name: 'alchemy',
   });
diff --git a/keyserver/src/utils/validation-utils.test.js b/keyserver/src/utils/validation-utils.test.js
--- a/keyserver/src/utils/validation-utils.test.js
+++ b/keyserver/src/utils/validation-utils.test.js
@@ -12,42 +12,52 @@
   });
 
   it('should redact a string inside an object', () => {
-    const validator = tShape({ password: tPassword });
+    const validator = tShape<{ +password: string }>({ password: tPassword });
     const object = { password: 'password' };
     const redacted = { password: redactedString };
     expect(sanitizeInput(validator, object)).toStrictEqual(redacted);
   });
 
   it('should redact an optional string', () => {
-    const validator = tShape({ password: t.maybe(tPassword) });
+    const validator = tShape<{ +password: ?string }>({
+      password: t.maybe(tPassword),
+    });
     const object = { password: 'password' };
     const redacted = { password: redactedString };
     expect(sanitizeInput(validator, object)).toStrictEqual(redacted);
   });
 
   it('should redact a string in optional object', () => {
-    const validator = tShape({ obj: t.maybe(tShape({ password: tPassword })) });
+    const validator = tShape<{ +obj?: ?{ +password: string } }>({
+      obj: t.maybe(tShape<{ +password: string }>({ password: tPassword })),
+    });
     const object = { obj: { password: 'password' } };
     const redacted = { obj: { password: redactedString } };
     expect(sanitizeInput(validator, object)).toStrictEqual(redacted);
   });
 
   it('should redact a string array', () => {
-    const validator = tShape({ passwords: t.list(tPassword) });
+    const validator = tShape<{ +passwords: $ReadOnlyArray<string> }>({
+      passwords: t.list(tPassword),
+    });
     const object = { passwords: ['password', 'password'] };
     const redacted = { passwords: [redactedString, redactedString] };
     expect(sanitizeInput(validator, object)).toStrictEqual(redacted);
   });
 
   it('should redact a string inside a dict', () => {
-    const validator = tShape({ passwords: t.dict(t.String, tPassword) });
+    const validator = tShape<{ +passwords: { +[string]: string } }>({
+      passwords: t.dict(t.String, tPassword),
+    });
     const object = { passwords: { a: 'password', b: 'password' } };
     const redacted = { passwords: { a: redactedString, b: redactedString } };
     expect(sanitizeInput(validator, object)).toStrictEqual(redacted);
   });
 
   it('should redact password dict key', () => {
-    const validator = tShape({ passwords: t.dict(tPassword, t.Bool) });
+    const validator = tShape<{ +passwords: { +[string]: boolean } }>({
+      passwords: t.dict(tPassword, t.Bool),
+    });
     const object = { passwords: { password1: true, password2: false } };
     const redacted: { +passwords: { [string]: mixed } } = { passwords: {} };
     redacted.passwords[redactedString] = false;
@@ -55,7 +65,9 @@
   });
 
   it('should redact a string inside a union', () => {
-    const validator = tShape({
+    const validator = tShape<{
+      +password: string | boolean,
+    }>({
       password: t.union([tPassword, t.String, t.Bool]),
     });
     const object = { password: 'password' };
@@ -64,7 +76,11 @@
   });
 
   it('should redact a string inside an object array', () => {
-    const validator = tShape({
+    const validator = tShape<{
+      +passwords: $ReadOnlyArray<{
+        +password: string,
+      }>,
+    }>({
       passwords: t.list(tShape({ password: tPassword })),
     });
     const object = { passwords: [{ password: 'password' }] };