diff --git a/src/manifest.rs b/src/manifest.rs
index e86e316..764f8de 100644
--- a/src/manifest.rs
+++ b/src/manifest.rs
@@ -4,6 +4,7 @@ use std::io::prelude::*;
 use console::style;
 use emoji;
 use failure::Error;
+use indicatif::MultiProgress;
 use progressbar;
 use serde_json;
 use toml;
@@ -17,20 +18,20 @@ struct CargoManifest {
 struct CargoPackage {
     name: String,
     authors: Vec<String>,
-    description: String,
+    description: Option<String>,
     version: String,
-    license: String,
-    repository: String,
+    license: Option<String>,
+    repository: Option<String>,
 }
 
 #[derive(Serialize)]
 struct NpmPackage {
     name: String,
     collaborators: Vec<String>,
-    description: String,
+    description: Option<String>,
     version: String,
-    license: String,
-    repository: Repository,
+    license: Option<String>,
+    repository: Option<Repository>,
     files: Vec<String>,
 }
 
@@ -64,10 +65,10 @@ impl CargoManifest {
             description: self.package.description,
             version: self.package.version,
             license: self.package.license,
-            repository: Repository {
+            repository: self.package.repository.map(|repo_url| Repository {
                 ty: "git".to_string(),
-                url: self.package.repository,
-            },
+                url: repo_url,
+            }),
             files: vec![js_file, wasm_file],
         }
     }
@@ -80,14 +81,41 @@ pub fn write_package_json(path: &str, scope: Option<String>) -> Result<(), Error
         style("[4/7]").bold().dim(),
         emoji::MEMO
     );
-    let pb = progressbar::new(step);
+
+    let warn = |field| {
+        format!(
+            "{} {}: Field {} is missing from Cargo.toml. It is not necessary, but recommended",
+            emoji::WARN,
+            style("[WARN]").bold().dim(),
+            field
+        )
+    };
+
+    let m = MultiProgress::new();
+    let pb = m.add(progressbar::new(step));
+
     let pkg_file_path = format!("{}/pkg/package.json", path);
     let mut pkg_file = File::create(pkg_file_path)?;
     let crate_data = read_cargo_toml(path)?;
     let npm_data = crate_data.into_npm(scope);
+
+    if npm_data.description.is_none() {
+        let warn_pb = m.add(progressbar::new(warn("description")));
+        warn_pb.finish();
+    }
+    if npm_data.repository.is_none() {
+        let warn_pb = m.add(progressbar::new(warn("repository")));
+        warn_pb.finish();
+    }
+    if npm_data.license.is_none() {
+        let warn_pb = m.add(progressbar::new(warn("license")));
+        warn_pb.finish();
+    }
+
     let npm_json = serde_json::to_string_pretty(&npm_data)?;
     pkg_file.write_all(npm_json.as_bytes())?;
     pb.finish();
+    m.join_and_clear()?;
     Ok(())
 }
 
diff --git a/tests/fixtures/bad-cargo-toml/Cargo.lock b/tests/fixtures/bad-cargo-toml/Cargo.lock
new file mode 100644
index 0000000..c6d7d32
--- /dev/null
+++ b/tests/fixtures/bad-cargo-toml/Cargo.lock
@@ -0,0 +1,140 @@
+[[package]]
+name = "bad-cargo-toml"
+version = "0.1.0"
+dependencies = [
+ "wasm-bindgen 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "dtoa"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "fnv"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "itoa"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "num-traits"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "proc-macro2"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "quote"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "serde"
+version = "1.0.33"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "serde_derive"
+version = "1.0.33"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive_internals 0.21.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.12.14 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "serde_derive_internals"
+version = "0.21.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.12.14 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "serde_json"
+version = "1.0.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "dtoa 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itoa 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "syn"
+version = "0.12.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "wasm-bindgen"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "wasm-bindgen-macro 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "wasm-bindgen-macro"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.12.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "wasm-bindgen-shared 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "wasm-bindgen-shared"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[metadata]
+"checksum dtoa 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "09c3753c3db574d215cba4ea76018483895d7bff25a31b49ba45db21c48e50ab"
+"checksum fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2fad85553e09a6f881f739c29f0b00b0f01357c743266d478b68951ce23285f3"
+"checksum itoa 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)" = "8324a32baf01e2ae060e9de58ed0bc2320c9a2833491ee36cd3b4c414de4db8c"
+"checksum num-traits 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0b3c2bd9b9d21e48e956b763c9f37134dc62d9e95da6edb3f672cacb6caf3cd3"
+"checksum proc-macro2 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "cd07deb3c6d1d9ff827999c7f9b04cdfd66b1b17ae508e14fe47b620f2282ae0"
+"checksum quote 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "1eca14c727ad12702eb4b6bfb5a232287dcf8385cb8ca83a3eeaf6519c44c408"
+"checksum serde 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)" = "4fe95aa0d46f04ce5c3a88bdcd4114ecd6144ed0b2725ebca2f1127744357807"
+"checksum serde_derive 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)" = "23b163a6ce7e1aa897919f9d8e40bd1f8a6f95342ed57727ae31387a01a7a356"
+"checksum serde_derive_internals 0.21.0 (registry+https://github.com/rust-lang/crates.io-index)" = "370aa477297975243dc914d0b0e1234927520ec311de507a560fbd1c80f7ab8c"
+"checksum serde_json 1.0.11 (registry+https://github.com/rust-lang/crates.io-index)" = "fab6c4d75bedcf880711c85e39ebf8ccc70d0eba259899047ec5d7436643ee17"
+"checksum syn 0.12.14 (registry+https://github.com/rust-lang/crates.io-index)" = "8c5bc2d6ff27891209efa5f63e9de78648d7801f085e4653701a692ce938d6fd"
+"checksum unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fc72304796d0818e357ead4e000d19c9c174ab23dc11093ac919054d20a6a7fc"
+"checksum wasm-bindgen 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "717507a3c7ef09d740c6d781bda57ba054d7b776f3e27d4478e25a773afd2e4b"
+"checksum wasm-bindgen-macro 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "cbc1a194a8fe6319f9f326f0c03d2083d61727ace574f9b1df083bad79a314ad"
+"checksum wasm-bindgen-shared 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "8b7cf730a826f1ec1ea2143d8582d5d2d27c0775035652daf0e0337225e8566b"
diff --git a/tests/fixtures/bad-cargo-toml/Cargo.toml b/tests/fixtures/bad-cargo-toml/Cargo.toml
new file mode 100644
index 0000000..36d09ac
--- /dev/null
+++ b/tests/fixtures/bad-cargo-toml/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "bad-cargo-toml"
+version = "0.1.0"
+authors = ["Michael Gattozzi <mgattozzi@gmail.com>"]
+
+[dependencies]
+wasm-bindgen = "0.1"
diff --git a/tests/fixtures/bad-cargo-toml/README.md b/tests/fixtures/bad-cargo-toml/README.md
new file mode 100644
index 0000000..1aa80a4
--- /dev/null
+++ b/tests/fixtures/bad-cargo-toml/README.md
@@ -0,0 +1,2 @@
+# bad-cargo-toml
+> an example rust -> wasm project
diff --git a/tests/fixtures/bad-cargo-toml/src/lib.rs b/tests/fixtures/bad-cargo-toml/src/lib.rs
new file mode 100644
index 0000000..d4fb8e9
--- /dev/null
+++ b/tests/fixtures/bad-cargo-toml/src/lib.rs
@@ -0,0 +1,15 @@
+#![feature(proc_macro)]
+
+extern crate wasm_bindgen;
+
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+extern {
+    fn alert(s: &str);
+}
+
+#[wasm_bindgen]
+pub fn greet(name: &str) {
+    alert(&format!("Hello, {}!", name));
+}