diff --git a/src/api/common/schema-validator.js b/src/api/common/schema-validator.js
index da0e3a58..aef431d1 100644
--- a/src/api/common/schema-validator.js
+++ b/src/api/common/schema-validator.js
@@ -1,4 +1,6 @@
+/* @flow */
 'use strict';
+
 const _ = require('lodash');
 const fs = require('fs');
 const path = require('path');
@@ -16,9 +18,10 @@ function isValidLedgerHash(ledgerHash) {
   return core.UInt256.is_valid(ledgerHash);
 }
 
-function loadSchema(filepath) {
+function loadSchema(filepath: string): {} {
   try {
-    return JSON.parse(fs.readFileSync(filepath, 'utf8'));
+    const schemaContent: any = fs.readFileSync(filepath, 'utf8');
+    return JSON.parse(schemaContent);
   } catch (e) {
     throw new Error('Failed to parse schema: ' + filepath);
   }
@@ -43,7 +46,7 @@ function formatSchemaErrors(errors) {
   return errors.map(formatSchemaError).join(', ');
 }
 
-function schemaValidate(schemaName, object) {
+function schemaValidate(schemaName: string, object: any): void {
   const formats = {address: isValidAddress,
                    ledgerHash: isValidLedgerHash};
   const options = {schemas: SCHEMAS, formats: formats,
diff --git a/src/api/common/utils.js b/src/api/common/utils.js
index 2a61a1eb..dd47e066 100644
--- a/src/api/common/utils.js
+++ b/src/api/common/utils.js
@@ -1,17 +1,20 @@
+/* @flow */
 'use strict';
 const BigNumber = require('bignumber.js');
 const core = require('../../core');
 const errors = require('./errors');
 
-function dropsToXrp(drops) {
+type Amount = {currency: string, issuer: string, value: string}
+
+function dropsToXrp(drops: string): string {
   return (new BigNumber(drops)).dividedBy(1000000.0).toString();
 }
 
-function xrpToDrops(xrp) {
+function xrpToDrops(xrp: string): string {
   return (new BigNumber(xrp)).times(1000000.0).floor().toString();
 }
 
-function toRippledAmount(amount) {
+function toRippledAmount(amount: Amount): string|Amount {
   if (amount.currency === 'XRP') {
     return xrpToDrops(amount.value);
   }
@@ -22,7 +25,9 @@ function toRippledAmount(amount) {
   };
 }
 
-function wrapCatch(asyncFunction: () => void): () => void {
+type AsyncFunction = (...x: any) => void
+
+function wrapCatch(asyncFunction: AsyncFunction): AsyncFunction {
   return function() {
     try {
       asyncFunction.apply(this, arguments);
@@ -33,7 +38,10 @@ function wrapCatch(asyncFunction: () => void): () => void {
   };
 }
 
-function composeAsync(wrapper, callback) {
+type Callback = (err: any, data: any) => void
+type Wrapper = (data: any) => any
+
+function composeAsync(wrapper: Wrapper, callback: Callback): Callback {
   return function(error, data) {
     if (error) {
       callback(error);
@@ -50,7 +58,7 @@ function composeAsync(wrapper, callback) {
   };
 }
 
-function convertExceptions(f) {
+function convertExceptions<T>(f: () => T): () => T {
   return function() {
     try {
       return f.apply(this, arguments);
diff --git a/src/api/common/validate.js b/src/api/common/validate.js
index b15dd4d1..63257aca 100644
--- a/src/api/common/validate.js
+++ b/src/api/common/validate.js
@@ -1,3 +1,4 @@
+/* @flow */
 'use strict';
 const _ = require('lodash');
 const core = require('./utils').core;
@@ -8,7 +9,7 @@ function error(text) {
   return new ValidationError(text);
 }
 
-function validateAddressAndSecret(obj) {
+function validateAddressAndSecret(obj: {address: string, secret: string}): void {
   const address = obj.address;
   const secret = obj.secret;
   schemaValidate('address', address);
@@ -22,7 +23,7 @@ function validateAddressAndSecret(obj) {
   }
 }
 
-function validateSecret(secret) {
+function validateSecret(secret: string): void {
   if (!secret) {
     throw error('Parameter missing: secret');
   }
diff --git a/src/api/ledger/utils.js b/src/api/ledger/utils.js
index cf4614b5..46d80534 100644
--- a/src/api/ledger/utils.js
+++ b/src/api/ledger/utils.js
@@ -1,3 +1,4 @@
+/* @flow */
 'use strict';
 const _ = require('lodash');
 const assert = require('assert');
@@ -5,19 +6,23 @@ const common = require('../common');
 const dropsToXrp = common.dropsToXrp;
 const composeAsync = common.composeAsync;
 
-function clamp(value, min, max) {
+type Callback = (err: any, data: any) => void
+
+function clamp(value: number, min: number, max: number): number {
   assert(min <= max, 'Illegal clamp bounds');
   return Math.min(Math.max(value, min), max);
 }
 
-function getXRPBalance(remote, address, ledgerVersion, callback) {
+function getXRPBalance(remote: any, address: string, ledgerVersion?: number, callback: Callback): void {
   remote.requestAccountInfo({account: address, ledger: ledgerVersion},
     composeAsync((data) => dropsToXrp(data.account_data.Balance), callback));
 }
 
+type Getter = (marker: ?string, limit: number, callback: Callback) => void
+
 // If the marker is omitted from a response, you have reached the end
 // getter(marker, limit, callback), callback(error, {marker, results})
-function getRecursiveRecur(getter, marker, limit, callback) {
+function getRecursiveRecur(getter: Getter, marker?: string, limit: number, callback: Callback): void {
   getter(marker, limit, (error, data) => {
     if (error) {
       return callback(error);
@@ -34,11 +39,13 @@ function getRecursiveRecur(getter, marker, limit, callback) {
   });
 }
 
-function getRecursive(getter, limit, callback) {
+function getRecursive(getter: Getter, limit?: number, callback: Callback) {
   getRecursiveRecur(getter, undefined, limit || Infinity, callback);
 }
 
-function renameCounterpartyToIssuer(amount) {
+type Amount = {counterparty?: string, issuer?: string, value: string}
+
+function renameCounterpartyToIssuer(amount?: Amount): ?{issuer?: string} {
   if (amount === undefined) {
     return undefined;
   }
@@ -48,7 +55,9 @@ function renameCounterpartyToIssuer(amount) {
   return _.omit(withIssuer, 'counterparty');
 }
 
-function renameCounterpartyToIssuerInOrder(order) {
+type Order = {taker_gets: Amount, taker_pays: Amount}
+
+function renameCounterpartyToIssuerInOrder(order: Order) {
   const taker_gets = renameCounterpartyToIssuer(order.taker_gets);
   const taker_pays = renameCounterpartyToIssuer(order.taker_pays);
   const changes = {taker_gets: taker_gets, taker_pays: taker_pays};
@@ -70,7 +79,9 @@ function signum(num) {
  *  @returns {Number} [-1, 0, 1]
  */
 
-function compareTransactions(first, second) {
+type Outcome = {outcome: {ledgerVersion: string, indexInLedger: string}};
+
+function compareTransactions(first: Outcome, second: Outcome): number {
   if (first.outcome.ledgerVersion === second.outcome.ledgerVersion) {
     return signum(Number(first.outcome.indexInLedger) -
       Number(second.outcome.indexInLedger));
@@ -79,7 +90,8 @@ function compareTransactions(first, second) {
     Number(second.outcome.ledgerVersion) ? -1 : 1;
 }
 
-function hasCompleteLedgerRange(remote, minLedgerVersion, maxLedgerVersion) {
+function hasCompleteLedgerRange(remote: any, minLedgerVersion: number,
+                                maxLedgerVersion: number): boolean {
   const firstLedgerVersion = 32570; // earlier versions have been lost
   return remote.getServer().hasLedgerRange(
     minLedgerVersion || firstLedgerVersion,