diff --git a/idl-parser/src/ffi/ast/mod.rs b/idl-parser/src/ffi/ast/mod.rs
index afffd597..9526123c 100644
--- a/idl-parser/src/ffi/ast/mod.rs
+++ b/idl-parser/src/ffi/ast/mod.rs
@@ -1,18 +1,43 @@
 use crate::ast;
-use std::{slice, str};
+use std::{
+    error::Error,
+    ffi::{c_char, CString},
+    slice, str,
+};
 
 pub mod visitor;
 
+#[repr(C)]
+pub enum ParseResult {
+    Success(*mut Program),
+    Error(*const c_char),
+}
+
 /// # Safety
 ///
 /// See the safety documentation of [`slice::from_raw_parts`].
 #[no_mangle]
-pub unsafe extern "C" fn parse_idl(idl_ptr: *const u8, idl_len: u32) -> *mut Program {
-    let idl = unsafe { slice::from_raw_parts(idl_ptr, idl_len.try_into().unwrap()) };
-    let idl = str::from_utf8(idl).unwrap();
-    let program = ast::parse_idl(idl).unwrap();
-    let program = Box::new(program);
-    Box::into_raw(program)
+pub unsafe extern "C" fn parse_idl(idl_ptr: *const u8, idl_len: u32) -> *mut ParseResult {
+    let idl_slice = unsafe { slice::from_raw_parts(idl_ptr, idl_len as usize) };
+    let idl_str = match str::from_utf8(idl_slice) {
+        Ok(s) => s,
+        Err(e) => return create_error(e, "validate idl_str"),
+    };
+
+    let program = match ast::parse_idl(idl_str) {
+        Ok(p) => p,
+        Err(e) => return create_error(e, "parse IDL"),
+    };
+
+    let program_box = Box::new(program);
+    let result = Box::new(ParseResult::Success(Box::into_raw(program_box)));
+    Box::into_raw(result)
+}
+
+fn create_error(e: impl Error, context: &str) -> *mut ParseResult {
+    let err_str = CString::new(format!("{}: {}", context, e)).unwrap();
+    let result = Box::new(ParseResult::Error(err_str.into_raw()));
+    Box::into_raw(result)
 }
 
 /// # Safety
diff --git a/js/example/src/catalog.ts b/js/example/src/catalog.ts
index c1edeb17..f93448b0 100644
--- a/js/example/src/catalog.ts
+++ b/js/example/src/catalog.ts
@@ -9,18 +9,20 @@ export type Part =
   | { slot: SlotPart };
 
 export interface FixedPart {
-  z: number | string | null;
+  z: number | null;
   metadata_uri: string;
 }
 
 export interface SlotPart {
-  equippable: Array<`0x${string}` | Uint8Array>;
-  z: number | string | null;
+  equippable: Array<string>;
+  z: number | null;
   metadata_uri: string;
 }
 
 export class RmrkCatalog {
-  private registry: TypeRegistry;
+  public readonly registry: TypeRegistry;
+  public readonly service: Service;
+
   constructor(public api: GearApi, public programId?: `0x${string}`) {
     const types: Record<string, any> = {
       Error: {"_enum":["PartIdCantBeZero","BadConfig","PartAlreadyExists","ZeroLengthPassed","PartDoesNotExist","WrongPartFormat","NotAllowedToCall"]},
@@ -32,6 +34,8 @@ export class RmrkCatalog {
     this.registry = new TypeRegistry();
     this.registry.setKnownTypes({ types });
     this.registry.register(types);
+
+    this.service = new Service(this);
   }
 
   newCtorFromCode(code: Uint8Array | Buffer): TransactionBuilder<null> {
@@ -63,104 +67,114 @@ export class RmrkCatalog {
     this.programId = builder.programId;
     return builder;
   }
+}
 
-  public addEquippables(part_id: number | string, collection_ids: Array<`0x${string}` | Uint8Array>): TransactionBuilder<{ ok: [number | string, Array<`0x${string}` | Uint8Array>] } | { err: Error }> {
-    return new TransactionBuilder<{ ok: [number | string, Array<`0x${string}` | Uint8Array>] } | { err: Error }>(
-      this.api,
-      this.registry,
+export class Service {
+  constructor(private _program: RmrkCatalog) {}
+
+  public addEquippables(part_id: number, collection_ids: Array<string>): TransactionBuilder<{ ok: [number, Array<string>] } | { err: Error }> {
+    if (!this._program.programId) throw new Error('Program ID is not set');
+    return new TransactionBuilder<{ ok: [number, Array<string>] } | { err: Error }>(
+      this._program.api,
+      this._program.registry,
       'send_message',
-      ['AddEquippables', part_id, collection_ids],
-      '(String, u32, Vec<[u8;32]>)',
+      ['Service', 'AddEquippables', part_id, collection_ids],
+      '(String, String, u32, Vec<[u8;32]>)',
       'Result<(u32, Vec<[u8;32]>), Error>',
-      this.programId
+      this._program.programId
     );
   }
 
-  public addParts(parts: Record<number | string, Part>): TransactionBuilder<{ ok: Record<number | string, Part> } | { err: Error }> {
-    return new TransactionBuilder<{ ok: Record<number | string, Part> } | { err: Error }>(
-      this.api,
-      this.registry,
+  public addParts(parts: Record<number, Part>): TransactionBuilder<{ ok: Record<number, Part> } | { err: Error }> {
+    if (!this._program.programId) throw new Error('Program ID is not set');
+    return new TransactionBuilder<{ ok: Record<number, Part> } | { err: Error }>(
+      this._program.api,
+      this._program.registry,
       'send_message',
-      ['AddParts', parts],
-      '(String, BTreeMap<u32, Part>)',
+      ['Service', 'AddParts', parts],
+      '(String, String, BTreeMap<u32, Part>)',
       'Result<BTreeMap<u32, Part>, Error>',
-      this.programId
+      this._program.programId
     );
   }
 
-  public removeEquippable(part_id: number | string, collection_id: `0x${string}` | Uint8Array): TransactionBuilder<{ ok: [number | string, `0x${string}` | Uint8Array] } | { err: Error }> {
-    return new TransactionBuilder<{ ok: [number | string, `0x${string}` | Uint8Array] } | { err: Error }>(
-      this.api,
-      this.registry,
+  public removeEquippable(part_id: number, collection_id: string): TransactionBuilder<{ ok: [number, string] } | { err: Error }> {
+    if (!this._program.programId) throw new Error('Program ID is not set');
+    return new TransactionBuilder<{ ok: [number, string] } | { err: Error }>(
+      this._program.api,
+      this._program.registry,
       'send_message',
-      ['RemoveEquippable', part_id, collection_id],
-      '(String, u32, [u8;32])',
+      ['Service', 'RemoveEquippable', part_id, collection_id],
+      '(String, String, u32, [u8;32])',
       'Result<(u32, [u8;32]), Error>',
-      this.programId
+      this._program.programId
     );
   }
 
-  public removeParts(part_ids: Array<number | string>): TransactionBuilder<{ ok: Array<number | string> } | { err: Error }> {
-    return new TransactionBuilder<{ ok: Array<number | string> } | { err: Error }>(
-      this.api,
-      this.registry,
+  public removeParts(part_ids: Array<number>): TransactionBuilder<{ ok: Array<number> } | { err: Error }> {
+    if (!this._program.programId) throw new Error('Program ID is not set');
+    return new TransactionBuilder<{ ok: Array<number> } | { err: Error }>(
+      this._program.api,
+      this._program.registry,
       'send_message',
-      ['RemoveParts', part_ids],
-      '(String, Vec<u32>)',
+      ['Service', 'RemoveParts', part_ids],
+      '(String, String, Vec<u32>)',
       'Result<Vec<u32>, Error>',
-      this.programId
+      this._program.programId
     );
   }
 
-  public resetEquippables(part_id: number | string): TransactionBuilder<{ ok: null } | { err: Error }> {
+  public resetEquippables(part_id: number): TransactionBuilder<{ ok: null } | { err: Error }> {
+    if (!this._program.programId) throw new Error('Program ID is not set');
     return new TransactionBuilder<{ ok: null } | { err: Error }>(
-      this.api,
-      this.registry,
+      this._program.api,
+      this._program.registry,
       'send_message',
-      ['ResetEquippables', part_id],
-      '(String, u32)',
+      ['Service', 'ResetEquippables', part_id],
+      '(String, String, u32)',
       'Result<Null, Error>',
-      this.programId
+      this._program.programId
     );
   }
 
-  public setEquippablesToAll(part_id: number | string): TransactionBuilder<{ ok: null } | { err: Error }> {
+  public setEquippablesToAll(part_id: number): TransactionBuilder<{ ok: null } | { err: Error }> {
+    if (!this._program.programId) throw new Error('Program ID is not set');
     return new TransactionBuilder<{ ok: null } | { err: Error }>(
-      this.api,
-      this.registry,
+      this._program.api,
+      this._program.registry,
       'send_message',
-      ['SetEquippablesToAll', part_id],
-      '(String, u32)',
+      ['Service', 'SetEquippablesToAll', part_id],
+      '(String, String, u32)',
       'Result<Null, Error>',
-      this.programId
+      this._program.programId
     );
   }
 
-  public async equippable(part_id: number | string, collection_id: `0x${string}` | Uint8Array, originAddress: string, value?: number | string | bigint, atBlock?: `0x${string}`): Promise<{ ok: boolean } | { err: Error }> {
-    const payload = this.registry.createType('(String, u32, [u8;32])', ['Equippable', part_id, collection_id]).toU8a();
-    const reply = await this.api.message.calculateReply({
-      destination: this.programId,
+  public async equippable(part_id: number, collection_id: string, originAddress: string, value?: number | string | bigint, atBlock?: `0x${string}`): Promise<{ ok: boolean } | { err: Error }> {
+    const payload = this._program.registry.createType('(String, String, u32, [u8;32])', ['Service', 'Equippable', part_id, collection_id]).toHex();
+    const reply = await this._program.api.message.calculateReply({
+      destination: this._program.programId,
       origin: decodeAddress(originAddress),
       payload,
       value: value || 0,
-      gasLimit: this.api.blockGasLimit.toBigInt(),
+      gasLimit: this._program.api.blockGasLimit.toBigInt(),
       at: atBlock || null,
     });
-    const result = this.registry.createType('(String, Result<bool, Error>)', reply.payload);
-    return result[1].toJSON() as unknown as { ok: boolean } | { err: Error };
+    const result = this._program.registry.createType('(String, String, Result<bool, Error>)', reply.payload);
+    return result[2].toJSON() as unknown as { ok: boolean } | { err: Error };
   }
 
-  public async part(part_id: number | string, originAddress: string, value?: number | string | bigint, atBlock?: `0x${string}`): Promise<Part | null> {
-    const payload = this.registry.createType('(String, u32)', ['Part', part_id]).toU8a();
-    const reply = await this.api.message.calculateReply({
-      destination: this.programId,
+  public async part(part_id: number, originAddress: string, value?: number | string | bigint, atBlock?: `0x${string}`): Promise<Part | null> {
+    const payload = this._program.registry.createType('(String, String, u32)', ['Service', 'Part', part_id]).toHex();
+    const reply = await this._program.api.message.calculateReply({
+      destination: this._program.programId,
       origin: decodeAddress(originAddress),
       payload,
       value: value || 0,
-      gasLimit: this.api.blockGasLimit.toBigInt(),
+      gasLimit: this._program.api.blockGasLimit.toBigInt(),
       at: atBlock || null,
     });
-    const result = this.registry.createType('(String, Option<Part>)', reply.payload);
-    return result[1].toJSON() as unknown as Part | null;
+    const result = this._program.registry.createType('(String, String, Option<Part>)', reply.payload);
+    return result[2].toJSON() as unknown as Part | null;
   }
 }
\ No newline at end of file
diff --git a/js/example/yarn.lock b/js/example/yarn.lock
index f52b8670..fa2f5201 100644
--- a/js/example/yarn.lock
+++ b/js/example/yarn.lock
@@ -514,10 +514,10 @@ bn.js@^5.2.1:
   resolved "https://registry.yarnpkg.com/bn.js/-/bn.js-5.2.1.tgz#0bc527a6a0d18d0aa8d5b0538ce4a77dccfa7b70"
   integrity sha512-eXRvHzWyYPBuB4NBy0cmYQjGitUrtqwbvlzP3G6VFnNRbsZQIxQ10PbKKHt8gZ/HW/D/747aDl+QkDqg3KQLMQ==
 
-commander@12.0.0:
-  version "12.0.0"
-  resolved "https://registry.yarnpkg.com/commander/-/commander-12.0.0.tgz#b929db6df8546080adfd004ab215ed48cf6f2592"
-  integrity sha512-MwVNWlYjDTtOjX5PiD7o5pK0UrFU/OYgcJfjjK4RaHZETNtjJqrZa9Y9ds88+A+f+d5lv+561eZ+yCKoS3gbAA==
+commander@12.1.0:
+  version "12.1.0"
+  resolved "https://registry.yarnpkg.com/commander/-/commander-12.1.0.tgz#01423b36f501259fdaac4d0e4d60c96c991585d3"
+  integrity sha512-Vw8qHK3bZM9y/P10u3Vib8o/DdkvA2OtPtZvD871QKjy74Wj1WSKFILMPRPSdUSx5RFK1arlJzEtA4PkFgnbuA==
 
 create-require@^1.1.0:
   version "1.1.1"
@@ -617,9 +617,9 @@ rxjs@^7.8.1:
     tslib "^2.1.0"
 
 "sails-js@file:../lib":
-  version "0.0.7"
+  version "0.1.4"
   dependencies:
-    commander "12.0.0"
+    commander "12.1.0"
 
 scale-ts@^1.6.0:
   version "1.6.0"
diff --git a/js/src/app.ts b/js/src/app.ts
index 05d530c8..b5efd5b9 100644
--- a/js/src/app.ts
+++ b/js/src/app.ts
@@ -25,6 +25,7 @@ const handler = async (path: string, out: string, name: string) => {
     generate(sails.parseIdl(idl), dir, file, name);
   } catch (e) {
     console.log(e.message, e.stack);
+    process.exit(1);
   }
 };
 
diff --git a/js/src/parser/parser.ts b/js/src/parser/parser.ts
index b1238bf0..38140f95 100644
--- a/js/src/parser/parser.ts
+++ b/js/src/parser/parser.ts
@@ -255,10 +255,31 @@ export class WasmParser {
     this._idlLen = null;
   }
 
+  private readCString = (ptr: number): string => {
+    const view = new DataView(this._memory.buffer);
+    let len = 0;
+    while (view.getUint8(ptr + len) !== 0) {
+      len++;
+    }
+    const buf = new Uint8Array(this._memory.buffer, ptr, len);
+    return new TextDecoder().decode(buf);
+  };
+
   public parse(idl: string): Program {
     this.fillMemory(idl);
 
-    const programPtr = this._instance.exports.parse_idl(this._memPtr, this._idlLen);
+    const resultPtr = this._instance.exports.parse_idl(this._memPtr, this._idlLen);
+
+    const view = new DataView(this._memory.buffer);
+    if (view.getUint32(resultPtr, true) == 1) { // Read ParseResult enum discriminant
+      // Error
+      const errorPtr = view.getUint32(resultPtr + 4, true);
+      const error = this.readCString(errorPtr);
+
+      throw new Error(error);
+    }
+
+    const programPtr = view.getUint32(resultPtr + 4, true);
 
     this._program = new Program();
     this._instance.exports.accept_program(programPtr, 0);