diff --git a/packages/api-format/src/util.js b/packages/api-format/src/util.js
index 68a6628121..0aaea0e206 100644
--- a/packages/api-format/src/util.js
+++ b/packages/api-format/src/util.js
@@ -3,7 +3,8 @@
 
 import type { FormatterFunction } from './types';
 
-const { isUndefined } = require('@polkadot/util/is');
+const assert = require('@polkadot/util/assert');
+const isUndefined = require('@polkadot/util/is/undefined');
 const formatNoop = require('./noop');
 
 const arrayTypeRegex = /\[\]$/;
@@ -25,9 +26,7 @@ function formatSingleType (formatters: { [any]: FormatterFunction }, type: strin
 }
 
 function formatArrayType (formatters: { [any]: FormatterFunction }, type: string, value: any): any {
-  if (!Array.isArray(value)) {
-    throw new Error(`Unable to format non-array '${value}' as '${type}'`);
-  }
+  assert(Array.isArray(value), `Unable to format non-array '${value}' as '${type}'`);
 
   type = type.replace(arrayTypeRegex, '');
 
diff --git a/packages/api-provider/src/http/index.js b/packages/api-provider/src/http/index.js
index 83c37b65ff..c2d5429737 100644
--- a/packages/api-provider/src/http/index.js
+++ b/packages/api-provider/src/http/index.js
@@ -5,6 +5,7 @@ import type { ProviderInterface } from '../types';
 
 require('./polyfill');
 
+const assert = require('@polkadot/util/assert');
 const JsonRpcCoder = require('../jsonRpcCoder');
 
 module.exports = class HttpProvider extends JsonRpcCoder implements ProviderInterface {
@@ -28,9 +29,7 @@ module.exports = class HttpProvider extends JsonRpcCoder implements ProviderInte
       method: 'POST'
     });
 
-    if (!response.ok) {
-      throw new Error(`[${response.status}]: ${response.statusText}`);
-    }
+    assert(response.ok, `[${response.status}]: ${response.statusText}`);
 
     const result = await response.json();
 
diff --git a/packages/api-provider/src/jsonRpcCoder.js b/packages/api-provider/src/jsonRpcCoder.js
index 496d968dd6..1089bdc793 100644
--- a/packages/api-provider/src/jsonRpcCoder.js
+++ b/packages/api-provider/src/jsonRpcCoder.js
@@ -3,33 +3,26 @@
 
 import type { JsonRpcRequest, JsonRpcResponse } from './types';
 
-const { isNumber, isUndefined } = require('@polkadot/util/is');
+const assert = require('@polkadot/util/assert');
+const isNumber = require('@polkadot/util/is/number');
+const isUndefined = require('@polkadot/util/is/undefined');
 
 module.exports = class JsonRpcCoder {
   _id: number = 0;
 
   decodeResponse (response: JsonRpcResponse): any {
-    if (!response) {
-      throw new Error('Empty response object received');
-    }
+    assert(response, 'Empty response object received');
 
-    if (response.jsonrpc !== '2.0') {
-      throw new Error('Invalid jsonrpc field in decoded object');
-    }
+    assert(response.jsonrpc === '2.0', 'Invalid jsonrpc field in decoded object');
 
-    if (!isNumber(response.id)) {
-      throw new Error('Invalid id field in decoded object');
-    }
+    assert(isNumber(response.id), 'Invalid id field in decoded object');
 
     if (response.error) {
       const { code, message } = response.error;
 
       throw new Error(`[${code}]: ${message}`);
     }
-
-    if (isUndefined(response.result)) {
-      throw new Error('No result found in JsonRpc response');
-    }
+    assert(!isUndefined(response.result), 'No result found in JsonRpc response');
 
     return response.result;
   }
diff --git a/packages/api/src/api.js b/packages/api/src/api.js
index bcffdb70ba..befb399f26 100644
--- a/packages/api/src/api.js
+++ b/packages/api/src/api.js
@@ -7,6 +7,7 @@ import type { ApiInterface } from './types';
 
 const { formatInputs, formatOutput } = require('@polkadot/api-format');
 const interfaces = require('@polkadot/api-jsonrpc');
+const assert = require('@polkadot/util/assert');
 const isFunction = require('@polkadot/util/is/function');
 const jsonrpcSignature = require('@polkadot/util/jsonrpc/signature');
 
@@ -16,13 +17,9 @@ module.exports = class Api implements ApiInterface {
   _stateInterface: any = null;
 
   constructor (provider: ProviderInterface) {
-    if (!provider) {
-      throw new Error('Instantiate the Api with `new Api(new Provider(...))`');
-    }
+    assert(provider, 'Instantiate the Api with `new Api(new Provider(...))`');
 
-    if (!isFunction(provider.send)) {
-      throw new Error('Supplied provider does not expose send method');
-    }
+    assert(isFunction(provider.send), 'Supplied provider does not expose send method');
 
     this._provider = provider;
 
@@ -49,9 +46,7 @@ module.exports = class Api implements ApiInterface {
 
         container[method] = async (..._params: Array<any>): any => {
           try {
-            if (inputs.length !== _params.length) {
-              throw new Error(`${inputs.length} params expected, found ${_params.length} instead`);
-            }
+            assert(inputs.length === _params.length, `${inputs.length} params expected, found ${_params.length} instead`);
 
             const params = formatInputs(inputs, _params);
             const result = await this._provider.send(rpcName, params);