pydantic-settings

name	pydantic-settings
description	Add or modify application configuration settings. Use when: adding new environment variables, settings fields, understanding settings conventions, working with secrets, or configuring optional vs required settings.

Pydantic Settings

context7: If the context7 tools are available, resolve and load the full pydantic-settings documentation before adding or modifying any settings:

context7_resolve-library-id: "pydantic-settings"
context7_query-docs: <resolved-id> "your query"

All application configuration is managed through the pydantic-settings library. Settings are defined in a single class and loaded from the environment and .env file.

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Key Rules

• One settings class: The main Settings class lives at library/conf/settings.py. Always update this existing class — never create a new settings class.
• Secrets use SecretStr or SecretBytes: Any value that is sensitive (passwords, tokens, API keys) must be wrapped in one of these types.
• Optional settings default to None: Never use empty strings as a sentinel for "not set".
• All fields use Field(): Include a description= for every field so operators know what it does.

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Pattern

# library/conf/settings.py
from pydantic import Field, SecretStr
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        env_file=".env",
        env_file_encoding="utf-8",
        extra="ignore",
    )

    # Regular setting with a default
    project_name: str = Field(default="library", description="Human-readable project name")

    # Optional sensitive setting — defaults to None, not empty string
    api_key: SecretStr | None = Field(
        default=None,
        description="API key for external service. Leave unset to disable.",
    )

    # Optional non-sensitive setting
    max_connections: int = Field(
        default=10,
        description="Maximum number of connections",
    )

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Accessing Secrets

SecretStr wraps the value to prevent accidental logging. Access the actual value explicitly when needed:

settings.api_key.get_secret_value() if settings.api_key else None

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Optional vs Required Fields

Pattern	Behavior
field: str = Field(...)	Required — raises ValidationError if not set
field: str = Field(default=x)	Optional with default
field: str | None = Field(default=None)	Optional, absent means None

Never use "" as a default for "not configured":

# Bad
smtp_host: str = Field(default="")

# Good
smtp_host: str | None = Field(default=None, description="SMTP server hostname. None disables email.")

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Environment Variable Naming

pydantic-settings maps field names to environment variable names automatically using the field name in uppercase:

project_name  →  PROJECT_NAME
database_url  →  DATABASE_URL

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Adding a New Setting

1. Open library/conf/settings.py.
2. Add the field to the existing Settings class with Field(description=...).
3. Use SecretStr if the value is sensitive.
4. Default to None (not "") if the setting is optional.
5. Update .env.example with the new variable name and a placeholder value or explanation.

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Developer Environment

• Settings are loaded from .env in the project root (gitignored).
• .env.example is the template for new developers — keep it updated with every new setting.

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Further Reading

• docs/dev/settings.md — Full settings developer guide covering all configuration modules, accessing settings in different component types, and environment variable conventions.
• Pydantic Settings Docs