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.
npx agentmods add skills/hyperactdoting/composer-plugin/joinnpx skills add hyperactdoting/composer-plugin --skill joingit clone --depth 1 https://github.com/hyperactdoting/composer-pluginWhat 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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00094 | $0.01900 |
| Opus 5 | $0.00047 | $0.00950 |
| Sonnet 5 | $0.00019 | $0.00380 |
| Haiku 4.5 | $0.00009 | $0.00190 |
Grade A, and why
join 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 yesterday.
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.
How it starts
The opening of the file, as written. The whole thing — 164 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Composer — Join a doc
Composer is a real-time collaborative markdown editor. composer_join_room
attaches you to an existing room so you can read, comment, suggest, and
respond to mentions.
When to load this skill
- The user pastes a
usecomposer.md/d/<id>URL. - They run
/composer:join <url>(the slash command delegates here). - They ask you to "watch this Composer doc" / "join this room" with a URL or roomId.
If they want to spin up a NEW doc from markdown they've shown you, that's
create, not join — load composer:create instead.
Talk like a person, not the MCP
Don't volunteer tool names, internal codes (COMPOSER_AUTH_REQUIRED,
HTTP statuses, 4403), file paths, or mechanics ("polling", "device
flow"). Translate tool results into plain language before relaying.
Verification and room URLs are the exceptions — the user clicks those,
paste them verbatim. If the user explicitly asks what's happening under
the hood, answer honestly. See composer:create ➜ "Talk like a person,
not the MCP" for the full guidance.
Steps
1. Sign in (kick this off immediately, every session)
Same as the composer:create skill: always call composer_login
first, before composer_join_room. If the user is already signed in,
it returns instantly and you proceed silently. If not, the first call
returns COMPOSER_AUTH_REQUIRED with a one-tap approval link — tell the
user once (warmly) that you've kicked off sign-in, paste the link
verbatim, and immediately call composer_login again to block until
they approve. A COMPOSER_AUTH_PENDING return means they haven't
approved yet — make sure they've seen the link, then call again to keep
waiting. See composer:create step 1 for the full pattern, including
the timeout copy and the "don't ask permission, just kick it off"
framing.
2. First-run only — agree on the agent's display name
If composer_join_room (step 4) returns an "ask the user what to call
you" error, no actingAs name is saved yet. Use the user.name from
composer_login to propose a default — "<FirstName>'s Agent" (e.g.
"Josh's Agent"). Account name missing or handle-like → fall back to
something playful: Monty, Gerty, Rosie, Otto, Pip. Never
suggest Claude, Gemini, Sonnet, Opus, Haiku, GPT, or any other model
name. Phrase as a single sentence the user can accept or override:
"I'll go by Josh's Agent in Composer docs — sound good?" Retry with
their answer as actingAs. The name persists to ~/.composer/user.json
and is reused forever — this step only happens once per machine.
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.
- yesterday First seen · 164 lines · 94 tokens per session scan A 38aeeb79bdf4
join is a skill published in the GitHub repository hyperactdoting/composer-plugin (2 stars, last pushed 2mo ago), licensed MIT. It adds 94 tokens to every session and 1,900 once invoked, about $0.0005 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 2026-08-31.
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