slack-shield

A small Python library and CLI for backfilling Slack channel history from an unlisted (non-Marketplace) Slack app under the 1 req/min, 15-msg/req rate limit. Resumable, checkpointed, zero infrastructure. MIT.

Source on GitHub → Code, install, issues, releases. Am I affected? → 30-second diagnostic. Pure browser, nothing sent anywhere. How it works (deep dive) → ~1,200-word write-up on the rate limit and the design. Install & quickstart → pip install, three CLI commands.

The problem in one paragraph

Since May 29, 2025, Slack throttles conversations.history and conversations.replies to 1 request per minute, max 15 messages per request for any commercially-distributed Slack app not listed on the Slack Marketplace. Existing installs switch over on March 3, 2026. That's 21,600 messages/channel/day at peak. A busy customer channel with half a million messages becomes a 23-day backfill. There's no clever way around the ceiling; Slack means it.

What slack-shield does

One request per minute per (workspace, route), exactly what Slack asks.
Honors Retry-After on every 429 (no fixed 60s sleep).
Walks the channel in time windows (default 7 days), paginates with limit=15, halves future windows when pagination gets heavy.
Checkpoints state after every successful page, so Ctrl-C / OOM / reboot resumes where it left off.
Writes messages as JSONL (one raw Slack message per line). Convert to CSV with slack-shield to-csv when done.
Zero infrastructure. No Redis, no Postgres, no Docker.

Use the right tool for your job

Your situation	Use
Need sane 429 retries in a regular Slack app	slack_sdk (official)
Personal/local archive with a user token	slackdump
Full Slack→Teams/Mattermost migration with files, channel mapping	CloudFuze, Cloudiway, 21b ($5k+)
Slack data into a warehouse	Airbyte, Fivetran
Compliance archive / eDiscovery	Pagefreezer, Onna, Archive360, ViewExport
Enterprise AI search over Slack	Glean ($50/user/mo, 100-seat min)
Bot/app token, unlisted Slack app, need to back-fill a customer's history under the 1 rpm limit, with state and resume, zero infra	slack-shield

Status

v0.1.0. Verified live against a real Slack workspace on 2026-05-14: auth, the 1 req/min pacing between requests, cursor pagination across pages, multi-window walk, state checkpoints, and resume from an interrupted run all behaved as documented. 28 pytest tests cover the components in isolation, including the 429 + Retry-After path and the adaptive-shrink path.