Agent skill

Phoenix LiveView Patterns

by georgeguimaraes in georgeguimaraes/elixir-agent-tools

Guidance for building and debugging Phoenix web interfaces: where LiveView loads data, scopes, PubSub topics, external polling and component state.

Apache-2.0Auto-check passedBackend & APIs

Install Phoenix LiveView Patterns

skills CLI

$ npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install georgeguimaraes/elixir-agent-tools phoenix --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/georgeguimaraes/elixir-agent-tools.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/elixir-dev/skills/phoenix .claude/skills/phoenix && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "phoenix" agent skill from https://github.com/georgeguimaraes/elixir-agent-tools/tree/main/plugins/elixir-dev/skills/phoenix into .claude/skills/phoenix/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phoenix", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/georgeguimaraes/elixir-agent-tools/tree/main/plugins/elixir-dev/skills/phoenix

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install georgeguimaraes/elixir-agent-tools phoenix --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/georgeguimaraes/elixir-agent-tools.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/elixir-dev/skills/phoenix .agents/skills/phoenix && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "phoenix" agent skill from https://github.com/georgeguimaraes/elixir-agent-tools/tree/main/plugins/elixir-dev/skills/phoenix into .agents/skills/phoenix/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phoenix", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install georgeguimaraes/elixir-agent-tools phoenix --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/georgeguimaraes/elixir-agent-tools.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/elixir-dev/skills/phoenix .cursor/skills/phoenix && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "phoenix" agent skill from https://github.com/georgeguimaraes/elixir-agent-tools/tree/main/plugins/elixir-dev/skills/phoenix into .cursor/skills/phoenix/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phoenix", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/georgeguimaraes/elixir-agent-tools.git --path plugins/elixir-dev/skills/phoenix

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install georgeguimaraes/elixir-agent-tools phoenix --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/georgeguimaraes/elixir-agent-tools.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/elixir-dev/skills/phoenix .gemini/skills/phoenix && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "phoenix" agent skill from https://github.com/georgeguimaraes/elixir-agent-tools/tree/main/plugins/elixir-dev/skills/phoenix into .gemini/skills/phoenix/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phoenix", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install georgeguimaraes/elixir-agent-tools phoenix

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/georgeguimaraes/elixir-agent-tools.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/elixir-dev/skills/phoenix .github/skills/phoenix && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "phoenix" agent skill from https://github.com/georgeguimaraes/elixir-agent-tools/tree/main/plugins/elixir-dev/skills/phoenix into .github/skills/phoenix/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phoenix", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install georgeguimaraes/elixir-agent-tools phoenix --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/georgeguimaraes/elixir-agent-tools.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/elixir-dev/skills/phoenix .opencode/skills/phoenix && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "phoenix" agent skill from https://github.com/georgeguimaraes/elixir-agent-tools/tree/main/plugins/elixir-dev/skills/phoenix into .opencode/skills/phoenix/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phoenix", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: phoenix
GitHub stars: 184
Token cost: ~1.3k tokens
SKILL.md length: 524 words
Files: 1
Skills in repo: 5
Repo updated: Sep 20, 2026
First seen: Oct 7, 2026
Licence: Apache-2.0

At a glance

Guidance for building and debugging Phoenix web interfaces: where LiveView loads data, scopes, PubSub topics, external polling and component state.

Deciding whether LiveView data belongs in mount or handle_params
SKILL.md covers Where to Load Data: mount vs…, Scopes: Security-First Pattern…, PubSub Topics Must Be Scoped and External Polling: GenServer,…, plus 4 more sections
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
Scoping PubSub topics and queries so tenants cannot see each other's data

What it does

The default is to load data in mount/3. The skill explains that mount and handle_params both run twice on first load, once as an HTTP dead render and once on the WebSocket connect, which is the LiveView lifecycle rather than a bug. handle_params/3 is for data that changes on live navigation through push_patch or patch links. When the double load really matters, it points to connected?(socket), assign_async/3 and assign_new/3 and notes what each one does not deduplicate.

Other patterns cover scopes, the Phoenix 1.8+ approach that threads authorization context through queries to prevent broken access control, PubSub topics that must be scoped by something like the organization or tenants see each other's data, external polling done by a single GenServer that broadcasts instead of every connected user calling the API, and the split between display-only functional components and LiveComponents that own state. The description also lists forms, routes, controllers, Plug and channels, and sends changesets and queries to the ecto skill.

When your agent uses it

Deciding whether LiveView data belongs in mount or handle_params
Scoping PubSub topics and queries so tenants cannot see each other's data
Debugging a LiveView that appears to load data twice
Moving external API polling out of individual LiveViews

Example prompts

“My LiveView runs the posts query twice on page load. Is that a bug?”
“Scope this PubSub subscription to the current organization.”
“Refactor our dashboard so one process polls the weather API and broadcasts to every LiveView.”

Requirements

An Elixir project that uses Phoenix

What it can do on your machine

Read from SKILL.md and the folder at commit ac3a5a1. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md (its code samples are elixir).
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Phoenix LiveView Patterns loads about 1.3k tokens when it runs. Until then it costs about 64 tokens; SKILL.md has 524 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~64
When it runs · the whole SKILL.md, loaded when a task matches: ~1.3k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from georgeguimaraes/elixir-agent-tools at commit ac3a5a1, republished under its Apache-2.0 licence (© georgeguimaraes). 524 words, ~1,307 tokens.

Download SKILL.mdSave it as .claude/skills/phoenix/SKILL.md (or your agent's skills folder).

name: phoenix
description: Build and debug Phoenix web interfaces and HTTP endpoints. Use for LiveView lifecycle and data loading, components, forms, routes, controllers, Plug, channels, and PubSub. Use ecto for changesets, queries, and persistence behind those interfaces.

Phoenix

Structure Phoenix interfaces, load LiveView data, and scope real-time updates.

Where to Load Data: mount vs handle_params

Default: load data in mount/3.

elixir

def mount(_params, _session, socket) do
  posts = Blog.list_posts(socket.assigns.current_scope)
  {:ok, assign(socket, posts: posts)}
end

Yes, mount runs twice on initial load (HTTP dead render + WebSocket connect). So does handle_params/3. That's the LiveView lifecycle, not a bug to route around. Moving queries from mount to handle_params does not dedupe them.

Use handle_params/3 for data that changes on live navigation (push_patch / <.link patch={...}>). mount does not re-run on patches, handle_params does.

elixir

def handle_params(%{"filter" => filter}, _uri, socket) do
  posts = Blog.list_posts(socket.assigns.current_scope, filter)
  {:noreply, assign(socket, posts: posts, filter: filter)}
end

When the initial double-load actually matters, the real tools are:

connected?(socket) to gate work to the connected render (loses SEO / no-JS rendering)
assign_async/3 to load after mount returns, in a separate process
assign_new/3 to reuse values already set on conn.assigns by upstream Plugs (e.g. :current_user), or shared from a parent LiveView. It does not dedupe arbitrary work across the dead/connected boundary: the function still runs on connected mount.

elixir

def mount(_params, _session, socket) do
  posts = if connected?(socket), do: Blog.list_posts(socket.assigns.current_scope), else: []
  {:ok, assign(socket, posts: posts)}
end

Scopes: Security-First Pattern (Phoenix 1.8+)

Scopes address OWASP #1 vulnerability: Broken Access Control. Authorization context is threaded automatically—no more forgetting to scope queries.

elixir

def list_posts(%Scope{user: user}) do
  Post |> where(user_id: ^user.id) |> Repo.all()
end

PubSub Topics Must Be Scoped

elixir

def subscribe(%Scope{organization: org}) do
  Phoenix.PubSub.subscribe(@pubsub, "posts:org:#{org.id}")
end

Unscoped topics = data leaks between tenants.

External Polling: GenServer, Not LiveView

Bad: Every connected user makes API calls (multiplied by users). Good: Single GenServer polls, broadcasts to all via PubSub.

Components Receive Data, LiveViews Own Data

Functional components: Display-only, no internal state
LiveComponents: Own state, handle own events
LiveViews: Full page, owns URL, top-level state

Async Data Loading

Use assign_async/3 for data that can load after mount:

elixir

def mount(_params, _session, socket) do
  {:ok, assign_async(socket, :user, fn -> {:ok, %{user: fetch_user()}} end)}
end

Gotchas from Core Team

LiveView terminate/2 Requires trap_exit

terminate/2 only fires if you're trapping exits—which you shouldn't do in LiveView.

Fix: Use a separate GenServer that monitors the LiveView process via Process.monitor/1, then handle :DOWN messages to run cleanup.

start_async Duplicate Names: Later Wins

Calling start_async with the same name while a task is in-flight: the later one wins, the previous task's result is ignored.

Fix: Call cancel_async/3 first if you want to abort the previous task.

Show full SKILL.md (206 more words)Show less

Channel Intercept Socket State is Stale

The socket in handle_out intercept is a snapshot from subscription time, not current state.

Why: Socket is copied into fastlane lookup at subscription time for performance.

Fix: Use separate topics per role, or fetch current state explicitly.

CSS Class Precedence is Stylesheet Order

When merging classes on components, precedence is determined by stylesheet order, not HTML order. If btn-primary appears later in the compiled CSS than bg-red-500, it wins regardless of HTML order.

Fix: Use variant props instead of class merging.

Upload Content-Type Can't Be Trusted

The :content_type in %Plug.Upload{} is user-provided. Always validate actual file contents (magic bytes) and rewrite filename/extension.

Read Body Before Plug.Parsers for Webhooks

To verify webhook signatures, you need the raw body. But Plug.Parsers consumes it.

elixir

{:ok, body, conn} = Plug.Conn.read_body(conn)
verify_signature!(conn, body)
%{conn | body_params: JSON.decode!(body)}

Don't use preserve_req_body: true—it keeps the entire body in memory for ALL requests.

Red Flags - STOP and Reconsider

Loading patch-mutable data in mount/3 instead of handle_params/3
Unscoped PubSub topics in multi-tenant app
LiveView polling external APIs directly
Using terminate/2 for cleanup (won't fire without trap_exit)
Calling start_async with same name without cancel_async first
Relying on socket.assigns in Channel intercepts (stale!)
CSS class merging for component customization (use variants)
Trusting %Plug.Upload{}.content_type for security

Any of these? Re-read the Gotchas section.

Files

Just SKILL.md in plugins/elixir-dev/skills/phoenix of georgeguimaraes/elixir-agent-tools.

Open the folder on GitHubat commit ac3a5a1

Compare with similar skills

Phoenix LiveView Patterns next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Phoenix LiveView Patterns compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Phoenix LiveView Patterns this skillgeorgeguimaraes/elixir-agent-tools	184	—	~1.3k	Automated safety check: Pass	Apache-2.0	20 days ago
Django Access Reviewgetsentry/skills	1k	3 repos	~2.6k	Automated safety check: Notes	Apache-2.0	yesterday
Frontmcp Auth UIagentfront/frontmcp	146	—	~3.7k	Automated safety check: Pass	Apache-2.0	today
Configuring Horizoncoollabsio/coolify	63k	4 repos	~898	Automated safety check: Pass	MIT	today
Abp Authorizationabpframework/abp	14k	—	~1.3k	Automated safety check: Pass	LGPL-3.0	today
Tyrohasinhayder/tyro	685	—	~1.4k	Automated safety check: Pass	MIT	1 mo ago

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Questions about Phoenix LiveView Patterns

What does Phoenix LiveView Patterns do?

Guidance for building and debugging Phoenix web interfaces: where LiveView loads data, scopes, PubSub topics, external polling and component state. The default is to load data in mount/3. The skill explains that mount and handle_params both run twice on first load, once as an HTTP dead render and once on the WebSocket connect, which is the LiveView lifecycle rather than a bug.

When should I use Phoenix LiveView Patterns?

Phoenix LiveView Patterns fits situations like: deciding whether LiveView data belongs in mount or handle_params; scoping PubSub topics and queries so tenants cannot see each other's data; debugging a LiveView that appears to load data twice; moving external API polling out of individual LiveViews.

How do I install Phoenix LiveView Patterns in Claude Code?

Run `npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a claude-code`. Or copy the skill folder (plugins/elixir-dev/skills/phoenix in georgeguimaraes/elixir-agent-tools) into .claude/skills/phoenix in your project. Claude Code loads it when a task matches its description.

How do I install Phoenix LiveView Patterns in Codex?

Run `npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a codex`. Or copy the skill folder (plugins/elixir-dev/skills/phoenix in georgeguimaraes/elixir-agent-tools) into .agents/skills/phoenix in your project. Codex loads it when a task matches its description.

Can I use Phoenix LiveView Patterns in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add georgeguimaraes/elixir-agent-tools --skill phoenix -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/phoenix, .gemini/skills/phoenix, .github/skills/phoenix and .opencode/skills/phoenix in your project.

What does Phoenix LiveView Patterns need to run?

SKILL.md names no scripts, command-line tools or credentials: Phoenix LiveView Patterns is instructions for the agent only. Our summary lists: An Elixir project that uses Phoenix.

Does Phoenix LiveView Patterns access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Phoenix LiveView Patterns safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Phoenix LiveView Patterns use?

Phoenix LiveView Patterns is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Phoenix LiveView Patterns use?

About 1.3k tokens (SKILL.md is roughly 5.2k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Phoenix LiveView Patterns?

Skills that share tags, products or a category with Phoenix LiveView Patterns: Django Access Review (getsentry/skills, 1k stars), Frontmcp Auth UI (agentfront/frontmcp, 146 stars), Configuring Horizon (coollabsio/coolify, 63k stars) and Abp Authorization (abpframework/abp, 14k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Phoenix LiveView Patterns?

georgeguimaraes (a GitHub user) maintains it in georgeguimaraes/elixir-agent-tools, which has 184 GitHub stars. The repository holds 5 skills in this directory. The repository was last updated on September 20, 2026.

Source: georgeguimaraes/elixir-agent-tools on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install Phoenix LiveView Patterns

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Phoenix

Where to Load Data: mount vs handle_params

Scopes: Security-First Pattern (Phoenix 1.8+)

PubSub Topics Must Be Scoped

External Polling: GenServer, Not LiveView

Components Receive Data, LiveViews Own Data

Async Data Loading

Gotchas from Core Team

LiveView terminate/2 Requires trap_exit

start_async Duplicate Names: Later Wins

Channel Intercept Socket State is Stale

CSS Class Precedence is Stylesheet Order

Upload Content-Type Can't Be Trusted

Read Body Before Plug.Parsers for Webhooks

Red Flags - STOP and Reconsider

Files

Compare with similar skills

Similar skills

More from georgeguimaraes/elixir-agent-tools

Related

Questions about Phoenix LiveView Patterns