What is post-slack-message?

A workflow for sending a message to a Slack channel or replying in a Slack thread. Slack is a team chat service, and the workflow normally shows the message for confirmation before sending it.

Use it to prepare and post channel messages or thread replies, with optional confirmation before the Slack API sends them.

It reduces accidental posts by separating message composition from sending, while supporting immediate sending when explicitly requested.

post-slack-message — Skill for Claude Code by tomzx

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.

Any agent

npx skills add tomzx/agents --skill post-slack-message

Clone the repo

git clone --depth 1 https://github.com/tomzx/agents

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/tomzx/agents/post-slack-message/github.svg)](https://agentmods.dev/skills/tomzx/agents/post-slack-message)

Your own site

<a href="https://agentmods.dev/skills/tomzx/agents/post-slack-message"><img src="https://agentmods.dev/badge/skills/tomzx/agents/post-slack-message/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/tomzx/agents/post-slack-message"><img src="https://agentmods.dev/badge/skills/tomzx/agents/post-slack-message.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 83 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,877 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

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.

Model	Per session	Once invoked
Fable 5.1	$0.00083	$0.01877
Opus 5	$0.00042	$0.00938
Sonnet 5	$0.00017	$0.00375
Haiku 4.5	$0.00008	$0.00188

Measured 6d ago against content hash 6ef4ab47c2b7, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

post-slack-message 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 6d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (post_slack_message.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

skills/post-slack-message/SKILL.md · 146 lines

How it starts

The opening of the file, as written. The whole thing — 146 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Post Slack Message

Posts a message to a Slack channel or as a thread reply using post_slack_message.py (Slack Web API chat.postMessage). The compose-and-confirm flow lives in this skill so it can use the question tool; the script is the send primitive.

Behavior modes

Review mode (default): write the message to a temp file, then use the question tool to ask the user to confirm sending the content of that file. Nothing is posted until the user approves.
Immediate mode (--yes): skip the confirmation and post right away. Use this for fully unattended flows (scheduled jobs, automation, or a caller that has already shown the message to the user).

--yes (also -y, --send, --auto) is accepted in any position of the arguments.

Prerequisites

SLACK_TOKEN set. A bot token (xoxb-) only needs the token; a web/browser token (xoxc-) also needs SLACK_COOKIE (the xoxd- value), the same credentials used by slack-kb-individual and slack-cached. Place them in .env at the repo root or export them in the environment.
The target channel: a channel id, a Slack archive URL, or a channel name.

Inputs

channel: one of --channel <id>, --channel-url <url>, or --channel-name <name> (the name is resolved to an id via conversations.list). Exactly one is required.
thread_ts: optional --thread-ts <ts> to post as a thread reply; auto-detected when --channel-url points at a thread message.
message: the message body in Slack mrkdwn (*bold*, <@USERID> mentions, <https://url|label> links). Provided as a trailing argument, via --file <path>, or via --stdin. Exactly one source.
mode: --yes for immediate send; otherwise review mode.
dry-run: --dry-run resolves the channel and shows what would be posted without sending. Use it to pre-validate credentials and targeting.

Steps

1. Resolve inputs

Determine the channel (id/url/name) and the final message text. If the caller passed an explicit message string, use it verbatim. Otherwise compose the message from context, keeping it short and using Slack mrkdwn. Decide whether this is a thread reply (--thread-ts).

Read the full file on GitHub · 146 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

post_slack_message.py 11 KB runs code

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.

6d ago First seen · 146 lines · 83 tokens per session scan A 6ef4ab47c2b7

Subscribe to this mod's changes

post-slack-message is a skill published in the GitHub repository tomzx/agents (6 stars, last pushed yesterday), licensed MIT. It adds 83 tokens to every session and 1,877 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 2026-09-03.

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post-slack-message