Fast, efficient and easy-to-use JSON parser and serializer for Dart.
Crimson does not verify your JSON!

🚧 Crimson is still in early development and is not ready for production use.
Only parsing is supported for now 🚧

Features #

• 🏎️ Fast: Like really fast. Crimson parses JSON in a single pass.
• 🌻 Easy to use: Crimson is designed to be easy to use and understand.
• 💃 Flexible: Crimson can partially parse and serialize JSON.
• 🥶 Freezed support: Crimson supports freezed classes.
• 🪶 Lightweight: Crimson is lightweight and has no third-party dependencies.

Usage #

After adding Crimson to your pubspec.yaml, you can start annotating your classes with @json and optionally @JsonField():

import 'package:crimson/crimson.dart';

part 'tweet.g.dart';

@json
class Tweet {
  DateTime? createdAt;

  String? tweet;

  int? favoriteCount;
}

Now you just need to run pub run build_runner build to generate the necessary code.

import 'package:crimson/crimson.dart';

void main() {
  final jsonBytes = downloadTweets();
  final crimson = Crimson(jsonBytes);

  final tweets = crimson.parseTweetList();
}

That's it! You can now parse and serialize JSON with ease.

Ignoring fields #

Annotate properties with @jsonIgnore to ignore them:

@json
class Tweet {
  DateTime? created_at;

  String? tweet;

  @jsonIgnore
  int? favoriteCount;
}

Renaming fields #

Use the @JsonName() annotation to rename individual fields:

@json
class Tweet {
  @JsonName('created_at')
  DateTime? createdAt;

  @JsonName('text', aliases: {'alias1', 'alias2'})
  String? tweet;
}

The same works for enum values:

@json
enum TweetType {
  tweet,

  @JsonName('re-tweet')
  retweet,
}

If you want to rename all fields or enum values, you can use @jsonKebabCase and @jsonSnakeCase:

@jsonKebabCase
class Tweet {
  DateTime? createdAt; // created-at

  String? tweet; // tweet

  int? favoriteCount; // favorite-count
}

@jsonSnakeCase
enum PlaceType {
  country, // country
  largeCity, // large_city
  smallCity, // small_city
}

Custom converters #

You can use custom converters to convert between JSON and Dart types using the @JsonConvert() annotation:

@json
class Tweet {
  String? tweet;

  @JsonConvert(fromJson: jsonIntToBool, toJson: boolToJsonInt)
  bool? isFavorite;
}

bool jsonIntToBool(int json) => json >= 1;

int boolToJsonInt(bool value) => value ? 1 : 0;

Freezed Support #

Crimson supports classes annotated with @freezed from the freezed package.

import 'package:crimson/crimson.dart';

part 'tweet.g.dart';
part 'tweet.freezed.dart';

@freezed
class Tweet with _$Tweet {
  @json
  const factory Tweet({
    DateTime? created_at,
    @JsonField(name: 'text') String? tweet,
    int? reply_count,
    int? retweet_count,
    int? favorite_count,
  }) = _Tweet;
}

License #

Copyright 2022 Simon Choi

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.