ESPHome Component Development

ESPHome is a system to configure microcontrollers (ESP32, ESP8266, RP2040, LibreTiny-based chips) using YAML configuration files. It generates C++ firmware compiled via PlatformIO for remote control through home automation systems.

Project Architecture

ESPHome follows a **code-generation architecture**: Python parses YAML configs and generates C++ source code, which is then compiled and flashed to target microcontrollers.

Core Components

1. **Configuration System** (`esphome/config*.py`): YAML parsing, Voluptuous validation, schema definitions

2. **Code Generation** (`esphome/codegen.py`, `esphome/cpp_generator.py`): Python-to-C++ generation, templates, build flags

3. **Component System** (`esphome/components/`): Modular hardware/software components with platform-specific implementations

4. **Core Framework** (`esphome/core/`): Application lifecycle, hardware abstraction, component registration

5. **Dashboard** (`esphome/dashboard/`): Web interface for configuration, management, OTA updates

Supported Platforms

Tech Stack

Coding Standards

Python (PEP 8)

C++ (Google Style Guide + clang-tidy)

- Functions/methods/variables: `lower_snake_case`

- Classes/structs/enums: `UpperCamelCase`

- Top-level constants: `UPPER_SNAKE_CASE`

- Function-local constants: `lower_snake_case`

- Protected/private fields: `lower_snake_case_with_trailing_underscore_`

Field Visibility

1. Pointer lifetime issues (setters validate/store pointers from known lists)

2. Invariant coupling (fields must stay synchronized)

3. Resource management (setters perform cleanup/registration)

Component Structure

Directory Layout

```

components/[component_name]/

├── __init__.py # Configuration schema and code generation

├── [component].h # C++ header (if needed)

├── [component].cpp # C++ implementation (if needed)

└── [platform]/ # Platform-specific implementations

├── __init__.py # Platform configuration

├── [platform].h # Platform C++ header

└── [platform].cpp # Platform C++ implementation

```

Component Metadata

```python

DEPENDENCIES = ["required_component"] # Required components

AUTO_LOAD = ["auto_loaded_component"] # Auto-load components

CONFLICTS_WITH = ["incompatible_comp"] # Incompatible components

CODEOWNERS = ["@username"] # GitHub maintainers

MULTI_CONF = True # Allow multiple instances

```

Code Generation Patterns

Configuration Schema Pattern

```python

import esphome.codegen as cg

import esphome.config_validation as cv

from esphome.const import CONF_KEY, CONF_ID

CONF_PARAM = "param" # New constant (not in esphome/const.py)

my_component_ns = cg.esphome_ns.namespace("my_component")

MyComponent = my_component_ns.class_("MyComponent", cg.Component)

CONFIG_SCHEMA = cv.Schema({

cv.GenerateID(): cv.declare_id(MyComponent),

cv.Required(CONF_KEY): cv.string,

cv.Optional(CONF_PARAM, default=42): cv.int_,

}).extend(cv.COMPONENT_SCHEMA)

async def to_code(config):

var = cg.new_Pvariable(config[CONF_ID])

await cg.register_component(var, config)

cg.add(var.set_key(config[CONF_KEY]))

cg.add(var.set_param(config[CONF_PARAM]))

```

C++ Class Pattern

```cpp

namespace esphome::my_component {

class MyComponent : public Component {

public:

void setup() override;

void loop() override;

void dump_config() override;

void set_key(const std::string &key) { this->key_ = key; }

void set_param(int param) { this->param_ = param; }

protected:

std::string key_;

int param_{0};

};

} // namespace esphome::my_component

```

Common Component Examples

**Sensor:**

```python

from esphome.components import sensor

CONFIG_SCHEMA = sensor.sensor_schema(MySensor).extend(cv.polling_component_schema("60s"))

async def to_code(config):

var = await sensor.new_sensor(config)

await cg.register_component(var, config)

```

**Binary Sensor:**

```python

from esphome.components import binary_sensor

CONFIG_SCHEMA = binary_sensor.binary_sensor_schema().extend({ ... })

async def to_code(config):

var = await binary_binary_sensor.new_binary_sensor(config)

```

**Switch:**

```python

from esphome.components import switch

CONFIG_SCHEMA = switch.switch_schema().extend({ ... })

async def to_code(config):

var = await switch.new_switch(config)

```

Configuration Validation

Common Validators

Platform/Framework Constraints

Schema Extensions

```python

CONFIG_SCHEMA = cv.Schema({ ... })

.extend(cv.COMPONENT_SCHEMA)

.extend(uart.UART_DEVICE_SCHEMA)

.extend(i2c.i2c_device_schema(0x48))

.extend(spi.spi_device_schema(cs_pin_required=True))

```

Development Workflow

Setup

Testing

**Python Unit Tests:**

```bash

pytest

```

**C++ Static Analysis:**

```bash

clang-tidy

```

**Component YAML Tests:**

```bash

./script/test_build_components -c <component> -t <target>

```

**All Components Together:**

```bash

./script/test_component_grouping.py -e config --all

```

**Linting:**

```bash

python3 script/run-in-env.py pre-commit run

```

Key Files

Important Constraints

Best Practices

1. Use descriptive names over abbreviations

2. Prefix all member access with `this->`

3. Avoid `#define` for constants (use `const` or enums)

4. Extend existing component schemas where possible

5. Test components individually and in groups

6. Follow platform-specific constraints in validation schemas

7. Use `protected` fields by default for extensibility

8. Document complex validation logic