What is post-to-slack?

A tool for sending a message to a Slack channel, optionally mentioning someone or replying in a thread. Slack is a workplace chat service organized around channels and conversations.

Use it to post updates, share generated work, notify a team, mention a user, or reply to an existing Slack thread.

It handles the lookup needed to send messages to the correct channel or person instead of relying on unstable display names.

post-to-slack — Skill for Claude Code by atman-33

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 atman-33/workhub --skill post-to-slack

Clone the repo

git clone --depth 1 https://github.com/atman-33/workhub

Made for: Claude Code.

Or install authoring, the plugin that ships this one along with the rest of its 5 skills.

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/atman-33/workhub/post-to-slack/github.svg)](https://agentmods.dev/skills/atman-33/workhub/post-to-slack)

Your own site

<a href="https://agentmods.dev/skills/atman-33/workhub/post-to-slack"><img src="https://agentmods.dev/badge/skills/atman-33/workhub/post-to-slack/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/atman-33/workhub/post-to-slack"><img src="https://agentmods.dev/badge/skills/atman-33/workhub/post-to-slack.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 59 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 670 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.

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	$0.00059	$0.00670
Opus 5	$0.00030	$0.00335
Sonnet 5	$0.00012	$0.00134
Haiku 4.5	$0.00006	$0.00067

Measured 5d ago against content hash f6c5ac9e2f48, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

post-to-slack 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 5d 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.

plugins/authoring/skills/post-to-slack/SKILL.md · 59 lines

How it starts

The opening of the file, as written. The whole thing — 59 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Post to Slack

Resolves a channel name (or a user name for a mention) to its Slack ID before posting — the Slack MCP connector's send/search tools need IDs, not display names, and IDs are not stable across workspaces.

Steps

Determine the message body and the target channel. If the caller (a direct user request, or another skill such as report-pbl-progress) already gives an explicit channel ID (C...) and/or an already-resolved mention (<@U...>), skip straight to step 4 — don't re-resolve what's already unambiguous.
If the channel is given by name rather than ID, resolve it with the Slack MCP connector's slack_search_channels tool and take the matching channel's ID. If more than one channel plausibly matches, ask the user rather than guessing.
If a mention is wanted and given by name rather than user ID, resolve it with slack_search_users and format it as <@USERID> inline in the message text — Slack does not render @name as a mention, only the raw <@ID> form works.
Post with slack_send_message (thread_ts for a thread reply, reply_broadcast to also surface a thread reply in the channel). Return the message's permalink to the caller.

Reference

Failure modes

Channel not found: slack_search_channels found no match — confirm the exact channel name with the user; don't guess a close match.
User not found: same for slack_search_users when resolving a mention.
Message too long: 5000 characters per text element — split into a thread reply rather than truncating silently.
Can't post to Slack Connect (externally shared) channels: slack_send_message fails outright for these; tell the user rather than retrying.
Slack Canvas unavailable: slack_create_canvas returns not_supported_free_team on free-tier workspaces. This skill never uses Canvas for that reason — if a caller wants a richer document than a single message, that's out of this skill's scope.

Read the full file on GitHub · 59 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.

5d ago First seen · 59 lines · 59 tokens per session scan A f6c5ac9e2f48

Subscribe to this mod's changes

post-to-slack is a skill published in the GitHub repository atman-33/workhub (2 stars, last pushed today), licensed MIT. It adds 59 tokens to every session and 670 once invoked, about $0.0003 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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