home-assistant-development

A coding guide for building Home Assistant software, including custom integrations, add-ons, language-model tools, and MCP servers. Home Assistant is home-automation software.

In plain words
What is it for?
It is for writing and checking Python code under Home Assistant's custom-components or add-ons directories and connecting tools to its platforms.
Why use it?
It helps avoid incomplete integration files, outdated setup patterns, and changes that appear correct but require a full restart to work.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/magnusoverli/opencode/home-assistant-development
Any agent
npx skills add magnusoverli/opencode --skill home-assistant-development
Clone the repo
git clone --depth 1 https://github.com/magnusoverli/opencode

Made for: Claude Code, Codex.

Per session 89 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,280 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00089 $0.01280
Opus 5 $0.00044 $0.00640
Sonnet 5 $0.00018 $0.00256
Haiku 4.5 $0.00009 $0.00128

Measured 3d ago against content hash 5b75cba48510, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

home-assistant-development scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

ha_opencode/rootfs/opt/ha-mcp-server/skills/home-assistant-development/SKILL.md · 108 lines

How it starts

The opening of the file, as written. The whole thing — 108 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Developing for Home Assistant

This is code, not configuration. The consent rules still apply, and so does the rule that .storage/ and the other internal directories are off-limits.

Custom integrations

A custom integration lives at custom_components/<domain>/ and needs at least manifest.json and __init__.py. manifest.json carries domain, name, version, documentation, dependencies, codeowners, requirements, and iot_class — Home Assistant refuses to load an integration whose manifest is incomplete, and the error appears only in the log.

Points worth checking against the running version, because they change:

  • Config-flow vs YAML setup — new integrations are config-flow only.
  • async_setup_entry / async_unload_entry and the coordinator pattern (DataUpdateCoordinator) for anything that polls.
  • Entity naming: _attr_has_entity_name and _attr_name interact in a way that has changed more than once.
  • hass.config_entries.async_forward_entry_setups — the plural, awaited form.

Any change under custom_components/ needs a full Home Assistant restart. There is no reload for integration code. Say so, and ask.

Read the current developer documentation rather than recalling API shapes — get_integration_docs covers user-facing configuration, and https://developers.home-assistant.io is the reference for the code side.

Native LLM tool providers

Home Assistant has a native llm platform: Core and custom integrations expose curated tools through <integration>/llm.py and register an LLM API. Newer builds also serve those APIs over native MCP at /api/mcp/<API ID> — the built-in Assist API is /api/mcp/assist.

  • get_ha_llm_development_guide returns the upstream references and a starter template for writing an llm.py provider. Use it before writing one.
  • get_agent_capabilities (or the ha://agent/capabilities resource) reports whether the running instance actually has the native llm component and which native MCP endpoints answer.
  • This add-on cannot register tools with Home Assistant's llm platform. Registration is internal to integrations and custom integrations. What the add-on can do is consume a configured native LLM API over native MCP, which is what the optional homeassistant_native MCP server does.
  • Native tools are curated by Home Assistant and are the better choice for requests that fit the configured API. The add-on's own MCP server is for configuration editing, safe writes, validation, admin and development workflows, screenshots, updates, ESPHome, hab, Zigbee, and documentation lookup.

Read the full file on GitHub · 108 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 108 lines · 89 tokens per session scan A 5b75cba48510

Subscribe to this mod's changes

home-assistant-development is a skill published in the GitHub repository magnusoverli/opencode (362 stars, last pushed 3d ago), licensed Unlicense. It adds 89 tokens to every session and 1,280 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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