diff --git a/src/tools/cleaner.js b/src/tools/cleaner.js
index 9594212..31f1140 100644
--- a/src/tools/cleaner.js
+++ b/src/tools/cleaner.js
@@ -3,9 +3,9 @@
 const _ = require('lodash');
 const { defaults, pick, pipe } = require('lodash/fp');
 
-const isPlainObj = require('./data').isPlainObj;
-const recurseReplace = require('./data').recurseReplace;
-const flattenPaths = require('./data').flattenPaths;
+const { isPlainObj, getObjectType } = require('./data');
+const { recurseReplace } = require('./data');
+const { flattenPaths } = require('./data');
 
 const DEFAULT_BUNDLE = {
   authData: {},
@@ -43,11 +43,34 @@ const recurseReplaceBank = (obj, bank = {}) => {
     if (typeof out !== 'string') {
       return out;
     }
+
     Object.keys(bank).forEach(key => {
       // Escape characters (ex. {{foo}} => \\{\\{foo\\}\\} )
-      const s = String(key).replace(/[-[\]/{}()\\*+?.^$|]/g, '\\$&');
-      const re = new RegExp(s, 'g');
-      out = out.replace(re, bank[key]);
+      const escapedKey = String(key).replace(/[-[\]/{}()\\*+?.^$|]/g, '\\$&');
+      const matchesKey = new RegExp(escapedKey, 'g');
+
+      if (!matchesKey.test(out)) {
+        return;
+      }
+
+      const valueParts = out.split(/({{.*?}})/).filter(Boolean);
+      const replacementValue = bank[key];
+
+      if (valueParts.length > 1) {
+        if (_.isArray(replacementValue) || _.isPlainObject(replacementValue)) {
+          throw new TypeError(
+            [
+              'Cannot interpolate objects or arrays into a string.',
+              `You've sent an ${getObjectType(replacementValue)},`,
+              `which will get coerced to ${replacementValue}`
+            ].join(' ')
+          );
+        }
+
+        out = valueParts.join('').replace(matchesKey, replacementValue);
+      } else {
+        out = replacementValue;
+      }
     });
 
     return out;
diff --git a/src/tools/data.js b/src/tools/data.js
index 87013a0..9e276a2 100644
--- a/src/tools/data.js
+++ b/src/tools/data.js
@@ -14,6 +14,18 @@ const isPlainObj = o => {
 
 const comparison = (obj, needle) => obj === needle;
 
+const getObjectType = obj => {
+  if (_.isPlainObject(obj)) {
+    return 'Object';
+  }
+
+  if (_.isArray(obj)) {
+    return 'Array';
+  }
+
+  return _.capitalize(typeof obj);
+};
+
 // Returns a path for the deeply nested haystack where
 // you could find the needle. If the needle is a plain
 // object we try _.isEqual (which could be slow!).
@@ -130,8 +142,7 @@ const recurseExtract = (obj, matcher) => {
 const _IGNORE = {};
 
 // Flatten a nested object.
-const flattenPaths = (data, sep) => {
-  sep = sep || '.';
+const flattenPaths = (data, sep = '.') => {
   const out = {};
   const recurse = (obj, prop) => {
     prop = prop || '';
@@ -179,6 +190,7 @@ module.exports = {
   findMapDeep,
   flattenPaths,
   genId,
+  getObjectType,
   isPlainObj,
   jsonCopy,
   memoizedFindMapDeep,
diff --git a/test/create-request-client.js b/test/create-request-client.js
index 4e8fe46..db4a85a 100644
--- a/test/create-request-client.js
+++ b/test/create-request-client.js
@@ -534,4 +534,117 @@ describe('request client', () => {
       });
     });
   });
+
+  describe('resolves body and header curlies', () => {
+    it('should keep valid data types', () => {
+      const event = {
+        bundle: {
+          inputData: {
+            number: 123,
+            bool: true,
+            float: 123.456,
+            arr: [1, 2, 3]
+          }
+        }
+      };
+      const bodyInput = createInput({}, event, testLogger);
+      const request = createAppRequestClient(bodyInput);
+      return request({
+        url: 'http://zapier-httpbin.herokuapp.com/post',
+        method: 'POST',
+        body: {
+          number: '{{bundle.inputData.number}}',
+          bool: '{{bundle.inputData.bool}}',
+          float: '{{bundle.inputData.float}}',
+          arr: '{{bundle.inputData.arr}}'
+        }
+      }).then(response => {
+        const { json } = response.json;
+
+        json.number.should.eql(123);
+        json.bool.should.eql(true);
+        json.float.should.eql(123.456);
+        json.arr.should.eql([1, 2, 3]);
+      });
+    });
+
+    it('should interpolate strings', () => {
+      const event = {
+        bundle: {
+          inputData: {
+            resourceId: 123
+          },
+          authData: {
+            access_token: 'Let me in'
+          }
+        }
+      };
+      const bodyInput = createInput({}, event, testLogger);
+      const request = createAppRequestClient(bodyInput);
+      return request({
+        url: 'http://zapier-httpbin.herokuapp.com/post',
+        method: 'POST',
+        body: {
+          message: 'We just got #{{bundle.inputData.resourceId}}'
+        },
+        headers: {
+          Authorization: 'Bearer {{bundle.authData.access_token}}'
+        }
+      }).then(response => {
+        const { json, headers } = response.json;
+
+        json.message.should.eql('We just got #123');
+        headers.Authorization.should.eql('Bearer Let me in');
+      });
+    });
+
+    it('should throw when interpolating a string with an array', () => {
+      const event = {
+        bundle: {
+          inputData: {
+            badData: [1, 2, 3]
+          }
+        }
+      };
+      const bodyInput = createInput({}, event, testLogger);
+      const request = createAppRequestClient(bodyInput);
+      return request({
+        url: 'http://zapier-httpbin.herokuapp.com/post',
+        method: 'POST',
+        body: {
+          message: 'No arrays, thank you: {{bundle.inputData.badData}}'
+        }
+      }).should.be.rejectedWith(
+        "Cannot interpolate objects or arrays into a string. You've sent an Array, which will get coerced to 1,2,3"
+      );
+    });
+
+    it('should send flatten objects', () => {
+      const event = {
+        bundle: {
+          inputData: {
+            address: {
+              street: '123 Zapier Way',
+              city: 'El Mundo'
+            }
+          }
+        }
+      };
+      const bodyInput = createInput({}, event, testLogger);
+      const request = createAppRequestClient(bodyInput);
+      return request({
+        url: 'http://zapier-httpbin.herokuapp.com/post',
+        method: 'POST',
+        body: {
+          streetAddress: '{{bundle.inputData.address.street}}',
+          city: '{{bundle.inputData.address.city}}'
+        }
+      }).then(response => {
+        const { json } = response.json;
+
+        json.streetAddress.should.eql('123 Zapier Way');
+        json.city.should.eql('El Mundo');
+      });
+    });
+  });
 });