Improve README and add documentation structure

AGENTS.md

@@ -0,0 +1,24 @@
+# grape-swagger-entity
+
+Adapter for grape-swagger that parses Grape::Entity classes into OpenAPI schema definitions.
+
+## Quick Reference
+
+```bash
+bundle install          # Install dependencies
+bundle exec rspec       # Run tests
+bundle exec rubocop     # Run linter
+bundle exec rubocop -a  # Auto-fix linter issues
+```
+
+## Key Constraints
+
+- Ruby >= 3.0
+- All files must start with `# frozen_string_literal: true`
+- CHANGELOG.md entry required for every PR (danger enforces this)
+
+## Documentation
+
+- [Testing Patterns](docs/testing.md)
+- [Contributing Guidelines](docs/contributing.md)
+- [Architecture Overview](docs/architecture.md)

CHANGELOG.md

@@ -3,6 +3,7 @@
 #### Features
 
 * Your contribution here.
+* [#91](https://github.com/ruby-grape/grape-swagger-entity/pull/91): Improve README and add documentation structure - [@numbata](https://github.com/numbata).
 
 #### Fixes
 

README.md

@@ -6,15 +6,64 @@
 ## Table of Contents
 
 - [What is grape-swagger-entity?](#what-is-grape-swagger-entity)
+  - [What it does](#what-it-does)
+  - [Example Output](#example-output)
+- [Related Projects](#related-projects)
+- [Compatibility](#compatibility)
 - [Installation](#installation)
+- [Usage](#usage)
+  - [Basic Entity](#basic-entity)
+  - [Custom Model Description](#custom-model-description)
+  - [Entity References](#entity-references)
+  - [Documentation Options](#documentation-options)
 - [Development](#development)
 - [Contributing](#contributing)
 - [License](#license)
 
-
 ## What is grape-swagger-entity?
 
-A simple grape-swagger adapter to allow parse representers as response model
+This gem provides an adapter for [grape-swagger](https://github.com/ruby-grape/grape-swagger) that allows parsing [grape-entity](https://github.com/ruby-grape/grape-entity) classes to generate OpenAPI/Swagger model definitions automatically.
+
+### What it does
+
+- Generates `definitions` in your Swagger JSON from Grape::Entity exposures
+- Maps entity properties to OpenAPI schema properties with types and descriptions
+- Handles nested entities and entity references via `$ref`
+- Supports arrays, required fields, and documentation options
+
+### Example Output
+
+```json
+{
+  "definitions": {
+    "User": {
+      "type": "object",
+      "description": "User model",
+      "properties": {
+        "id": { "type": "integer", "description": "User ID" },
+        "name": { "type": "string", "description": "Full name" }
+      },
+      "required": ["id", "name"]
+    }
+  }
+}
+```
+
+## Related Projects
+
+- [Grape](https://github.com/ruby-grape/grape)
+- [Grape Entity](https://github.com/ruby-grape/grape-entity)
+- [Grape Swagger](https://github.com/ruby-grape/grape-swagger)
+- [Grape Swagger Representable](https://github.com/ruby-grape/grape-swagger-representable)
+
+## Compatibility
+
+This gem is tested with the following versions:
+
+| grape-swagger-entity | grape-swagger | grape-entity | grape   |
+|---------------------|---------------|--------------|---------|
+| 0.7.x               | >= 2.0.0      | >= 1.0.0     | >= 1.3  |
+| 0.6.x               | >= 1.2.0      | >= 0.6.0     | >= 1.3  |
 
 ## Installation
 
@@ -32,17 +81,63 @@ Or install it yourself as:
 
     $ gem install grape-swagger-entity
 
-## Development
+## Usage
+
+### Basic Entity
+
+Define your entities with `documentation` options to generate OpenAPI schema properties:
+
+```ruby
+class UserEntity < Grape::Entity
+  expose :id, documentation: { type: Integer, desc: 'User ID' }
+  expose :name, documentation: { type: String, desc: 'Full name' }
+  expose :email, documentation: { type: String, desc: 'Email address' }
+end
+```
+
+### Custom Model Description
 
-After checking out the repo, run `bin/setup` to install dependencies. Then, run `rspec` to run the tests. You can also run `bin/pry` for an interactive prompt that will allow you to experiment.
+Override the default "{ModelName} model" description by defining a `self.documentation` method. This feature is handled by [grape-swagger](https://github.com/ruby-grape/grape-swagger) (requires grape-swagger >= 2.2.0):
 
-To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
+```ruby
+class UserEntity < Grape::Entity
+  def self.documentation
+    { desc: 'Represents a user account with profile information' }
+  end
+
+  expose :id, documentation: { type: Integer, desc: 'User ID' }
+  expose :name, documentation: { type: String, desc: 'Full name' }
+end
+```
+
+### Entity References
+
+Use `using:` to reference other entities and `is_array:` for collections:
+
+```ruby
+class OrderEntity < Grape::Entity
+  expose :id, documentation: { type: Integer, desc: 'Order ID' }
+  expose :user, using: UserEntity,
+         documentation: { desc: 'The customer who placed this order' }
+  expose :items, using: ItemEntity,
+         documentation: { desc: 'Line items', is_array: true }
+end
+```
+
+### Documentation Options
+
+Common options: `type`, `desc`, `required`, `is_array`, `values`, `example`.
+
+See [full documentation options](docs/documentation-options.md) for all available options including validation constraints.
+
+## Development
+
+See [testing documentation](docs/testing.md) for development setup and running tests.
 
 ## Contributing
 
-Bug reports and pull requests are welcome on GitHub at https://github.com/ruby-grape/grape-swagger-entity.
+See [contributing guidelines](docs/contributing.md).
 
 ## License
 
 The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).
-

docs/architecture.md

@@ -0,0 +1,71 @@
+# Architecture Overview
+
+## Purpose
+
+This gem registers a model parser with grape-swagger that converts `Grape::Entity` classes into OpenAPI schema definitions.
+
+## Core Components
+
+```
+lib/grape-swagger/entity/
+├── parser.rb           # Main parser - converts Entity to OpenAPI schema
+├── attribute_parser.rb # Parses individual exposure attributes
+├── helper.rb           # Utility methods for model naming, discriminators
+└── version.rb          # Gem version
+```
+
+### Parser (`parser.rb`)
+
+Entry point for entity parsing. Responsibilities:
+- Extract exposures from Grape::Entity
+- Handle nested entities and `using:` references
+- Process `merge: true` exposures
+- Handle inheritance with `allOf` and discriminators
+- Determine required fields
+
+### AttributeParser (`attribute_parser.rb`)
+
+Converts individual exposure options to OpenAPI property schema:
+- Maps Ruby types to OpenAPI types
+- Handles arrays (`is_array: true`)
+- Processes enums (`values:`)
+- Adds constraints (min/max, minLength/maxLength)
+
+### Helper (`helper.rb`)
+
+Utilities for:
+- Model name resolution (strips Entity/Entities suffix)
+- Discriminator detection for inheritance
+- Root exposure extraction
+
+## Data Flow
+
+```
+Grape::Entity class
+       │
+       ▼
+   Parser.call
+       │
+       ├── extract_params (get exposures)
+       │
+       ├── parse_grape_entity_params
+       │         │
+       │         ├── AttributeParser (per exposure)
+       │         │
+       │         └── parse_nested (for nested blocks)
+       │
+       └── handle_discriminator (inheritance)
+       │
+       ▼
+[properties_hash, required_array]
+```
+
+## Integration Point
+
+Registered with grape-swagger in `lib/grape-swagger/entity.rb`:
+
+```ruby
+GrapeSwagger.model_parsers.register(GrapeSwagger::Entity::Parser, Grape::Entity)
+```
+
+grape-swagger calls `Parser.new(model, endpoint).call` when it encounters a `Grape::Entity` subclass.

docs/contributing.md

@@ -0,0 +1,57 @@
+# Contributing Guidelines
+
+## PR Requirements
+
+Every PR must include:
+
+1. **CHANGELOG.md entry** - Add under `### X.X.X (Next)` in the appropriate section:
+   ```markdown
+   #### Fixes
+   * [#123](https://github.com/ruby-grape/grape-swagger-entity/pull/123): Brief description - [@username](https://github.com/username).
+   ```
+
+2. **Passing CI** - RuboCop + RSpec must pass
+
+3. **Tests** - New functionality needs specs; bug fixes need regression tests
+
+## CHANGELOG Format
+
+```markdown
+### 0.7.1 (Next)
+
+#### Features
+
+* Your contribution here.
+
+#### Fixes
+
+* [#PR](URL): Description - [@author](URL).
+```
+
+- Use `Features` for new functionality
+- Use `Fixes` for bug fixes and maintenance
+
+## Commit Messages
+
+Follow conventional style:
+- `Fix #123: description` for bug fixes
+- `Add feature description` for features
+- `Update dependency/docs` for maintenance
+
+## Code Style
+
+RuboCop enforces style. Key rules:
+- `frozen_string_literal: true` pragma required
+- Consistent hash indentation
+- No trailing whitespace
+
+```bash
+bundle exec rubocop -a  # Auto-fix most issues
+```
+
+## Danger Checks
+
+CI runs danger which enforces:
+- CHANGELOG entry present
+- Table of Contents in README is current
+- PR has description

docs/documentation-options.md

@@ -0,0 +1,89 @@
+# Documentation Options
+
+The `documentation` hash in entity exposures supports the following options:
+
+## Type Options
+
+| Option | Description | Example |
+|--------|-------------|---------|
+| `type` | OpenAPI data type | `String`, `Integer`, `Boolean`, `Float`, `Date`, `DateTime` |
+| `is_array` | Marks field as array type | `true` / `false` |
+
+## Description Options
+
+| Option | Description | Example |
+|--------|-------------|---------|
+| `desc` | Property description | `'User email address'` |
+| `example` | Example value for documentation | `'user@example.com'` |
+| `default` | Default value | `'pending'` |
+
+## Validation Options
+
+| Option | Description | Example |
+|--------|-------------|---------|
+| `required` | Whether field is required | `true` / `false` |
+| `values` | Enum values (array or proc) | `%w[pending active]` or `-> { Status.all }` |
+| `minimum` | Minimum value for numeric types | `0` |
+| `maximum` | Maximum value for numeric types | `100` |
+| `min_length` | Minimum length for strings | `1` |
+| `max_length` | Maximum length for strings | `255` |
+| `min_items` | Minimum items for arrays | `1` |
+| `max_items` | Maximum items for arrays | `10` |
+| `unique_items` | Array items must be unique | `true` |
+
+## Display Options
+
+| Option | Description | Example |
+|--------|-------------|---------|
+| `read_only` | Marks field as read-only | `true` |
+| `hidden` | Hide field from documentation | `true` |
+
+## Examples
+
+### Basic types
+
+```ruby
+expose :id, documentation: { type: Integer, desc: 'Unique identifier' }
+expose :name, documentation: { type: String, desc: 'Full name', required: true }
+expose :active, documentation: { type: Boolean, default: true }
+```
+
+### Enums
+
+```ruby
+expose :status, documentation: {
+  type: String,
+  desc: 'Current status',
+  values: %w[pending active suspended]
+}
+```
+
+### Numeric constraints
+
+```ruby
+expose :age, documentation: {
+  type: Integer,
+  minimum: 0,
+  maximum: 150
+}
+```
+
+### String constraints
+
+```ruby
+expose :username, documentation: {
+  type: String,
+  min_length: 3,
+  max_length: 20
+}
+```
+
+### Arrays
+
+```ruby
+expose :tags, documentation: {
+  type: String,
+  is_array: true,
+  desc: 'Associated tags'
+}
+```