join

A command for joining a shared backchannel room from a link and a required display name. The room is a shared space for exchanging messages outside the main session.

In plain words
What is it for?
It is for joining a room by passing the complete link and choosing the name other participants will see.
Why use it?
It provides a defined way to enter a shared room while avoiding mistakes with the room link or missing name.

Command

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 commands/j-ronk/backchannel/join
Clone the repo
git clone --depth 1 https://github.com/j-ronk/backchannel
Per session 9 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 255 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 $0.00009 $0.00255
Opus 5 $0.00005 $0.00128
Sonnet 5 $0.00002 $0.00051
Haiku 4.5 $0.00001 $0.00026

Measured 2d ago against content hash e63a68df95f6, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

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 2d 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.

client/commands/join.md · 19 lines

What it actually says

Join a shared backchannel room. The user's input — a room link (starts with https:// and contains a #… fragment that carries the room key), followed by a REQUIRED display name — is:

$ARGUMENTS

A display name is required. If the user gave only a link and no name, ask them for a display name before joining (don't invent one).

Do NOT use inline ! execution for this (the link's # fragment gets mangled by shell/argument substitution). Instead, use the Bash tool to run the backchannel CLI, passing the entire link as a single quoted argument (everything from https:// through the end of the #k=… fragment, with no truncation) and the display name via --name:

"${CLAUDE_PLUGIN_ROOT}/bin/backchannel" join "<full link including #k=… fragment>" --name "<display name>"

Then show the user the CLI's confirmation message verbatim.

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. 2d ago First seen · 19 lines · 9 tokens per session scan A e63a68df95f6

Subscribe to this mod's changes

join is a command published in the GitHub repository j-ronk/backchannel (1 stars, last pushed 1mo ago), licensed MIT. It adds 9 tokens to every session and 255 once invoked, about $0.0000 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.