MCPInstall

flutter-implement-json-serialization

by flutterMobile

Create model classes with fromJson and toJson methods using dart:convert. Use when manually mapping JSON keys to class properties for simple data structures.

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37.6K
Last 24h
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#1229
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Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/flutter/agent-plugins --skill flutter-implement-json-serialization
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads flutter-implement-json-serialization automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

Security audits

Independent scans of the skill's instructions and bundled files.

Gen Agent Trust Hub PassSAFE ·This skill provides standard Flutter implementation patterns for manual JSON serialization and network fetching. It follows community best practices, including background parsing for performance and explicit type casting for safety.
Socket PassNo alerts
Snyk WarnMEDIUM ·Risk: MEDIUM · 1 issue

SKILL.md

The instructions your agent reads when the skill is triggered.

Serializing JSON Manually in Flutter

Contents

Core Guidelines

  • Import dart:convert: Utilize Flutter's built-in dart:convert library for manual JSON encoding (jsonEncode) and decoding (jsonDecode).
  • Enforce Type Safety: Always cast the dynamic result of jsonDecode() to the expected type, typically Map<String, dynamic> for objects or List<dynamic> for arrays.
  • Encapsulate Serialization Logic: Define plain model classes containing properties corresponding to the JSON structure. Implement a fromJson factory constructor and a toJson method within the model.
  • Handle Background Parsing: If parsing large JSON documents (execution time > 16ms), offload the parsing logic to a separate isolate using Flutter's compute() function to prevent UI jank.
  • Throw Exceptions on Failure: When handling HTTP responses, throw an exception if the status code is not successful (e.g., not 200 OK or 201 Created). Do not return null.

Workflow: Implementing a Serializable Model

Use this checklist to implement manual JSON serialization for a data model.

Task Progress:

  • Define the plain model class with final properties.
  • Implement the factory Model.fromJson(Map<String, dynamic> json) constructor.
  • Implement the Map<String, dynamic> toJson() method.
  • Write unit tests for both serialization methods.
  • Run validator -> review type mismatch errors -> fix casting logic.
  1. Define the Model: Create a class with properties matching the JSON keys.
  2. Implement fromJson: Extract values from the Map and cast them to the appropriate Dart types. Use pattern matching or explicit casting.
  3. Implement toJson: Return a Map<String, dynamic> mapping the class properties back to their JSON string keys.
  4. Validate: Execute unit tests to ensure type safety, autocompletion, and compile-time exception handling function correctly.

Workflow: Fetching and Parsing JSON

Use this conditional workflow when retrieving and parsing JSON from a network request.

Task Progress:

  • Execute the HTTP request.
  • Validate the response status code.
  • Determine parsing strategy (Synchronous vs. Isolate).
  • Decode and map the JSON to the model.
  1. Execute Request: Use the http package to perform the network call.
  2. Validate Response:
    • If response.statusCode == 200 (or 201 for POST), proceed to parsing.
    • If the status code indicates failure, throw an Exception.
  3. Determine Parsing Strategy:
    • If parsing a small payload (e.g., a single object), parse synchronously on the main thread.
    • If parsing a large payload (e.g., an array of thousands of objects), use compute(parseFunction, response.body) to parse in a background isolate.
  4. Decode and Map: Pass the decoded JSON to your model's fromJson constructor.

Examples

High-Fidelity Model Implementation

import 'dart:convert';

class User {
  final int id;
  final String name;
  final String email;

  const User({
    required this.id,
    required this.name,
    required this.email,
  });

  // Factory constructor for deserialization
  factory User.fromJson(Map<String, dynamic> json) {
    return switch (json) {
      {
        'id': int id,
        'name': String name,
        'email': String email,
      } => 
        User(
          id: id,
          name: name,
          email: email,
        ),
      _ => throw const FormatException('Failed to load User.'),
    };
  }

  // Method for serialization
  Map<String, dynamic> toJson() {
    return {
      'id': id,
      'name': name,
      'email': email,
    };
  }
}

Synchronous Parsing (Small Payload)

import 'dart:convert';
import 'package:http/http.dart' as http;

Future<User> fetchUser(http.Client client, int userId) async {
  final response = await client.get(
    Uri.parse('https://api.example.com/users/$userId'),
    headers: {'Accept': 'application/json'},
  );

  if (response.statusCode == 200) {
    // Decode returns dynamic, cast to Map<String, dynamic>
    final Map<String, dynamic> jsonMap = jsonDecode(response.body) as Map<String, dynamic>;
    return User.fromJson(jsonMap);
  } else {
    throw Exception('Failed to load user');
  }
}

Background Parsing (Large Payload)

import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;

// Top-level function required for compute()
List<User> parseUsers(String responseBody) {
  final parsed = (jsonDecode(responseBody) as List<dynamic>).cast<Map<String, dynamic>>();
  return parsed.map<User>((json) => User.fromJson(json)).toList();
}

Future<List<User>> fetchUsers(http.Client client) async {
  final response = await client.get(
    Uri.parse('https://api.example.com/users'),
    headers: {'Accept': 'application/json'},
  );

  if (response.statusCode == 200) {
    // Offload expensive parsing to a background isolate
    return compute(parseUsers, response.body);
  } else {
    throw Exception('Failed to load users');
  }
}

FAQ

What does the flutter-implement-json-serialization skill do?

Create model classes with fromJson and toJson methods using dart:convert. Use when manually mapping JSON keys to class properties for simple data structures.

How do I install flutter-implement-json-serialization?

Run npx skills add https://github.com/flutter/agent-plugins --skill flutter-implement-json-serialization in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/flutter-implement-json-serialization/ (personal) or .claude/skills/flutter-implement-json-serialization/ (project).

Which AI agents can use flutter-implement-json-serialization?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is flutter-implement-json-serialization safe to install?

Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk flagged items to review. As with any skill, read the SKILL.md and bundled scripts before installing.

Who maintains flutter-implement-json-serialization?

It is published by flutter in flutter/agent-plugins. It has 37,552 recorded installs.

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