Slack Web API Skill

Use this skill to run Slack Web API operations through uxc + OpenAPI.

Reuse the uxc skill for shared execution, auth, and error-handling guidance.

Prerequisites

• uxc is installed and available in PATH.
• Network access to https://slack.com/api.
• Access to the curated OpenAPI schema URL:

- https://raw.githubusercontent.com/holon-run/uxc/main/skills/slack-openapi-skill/references/slack-web.openapi.json

• A Slack bot token and, for selected thread/history reads, an optional user token.

Scope

This skill covers a Messaging Core surface:

• auth validation
• channel lookup and inspection
• conversation history reads
• thread replies reads
• posting messages, including replies via thread_ts
• adding reactions

This skill does not cover:

• Slack OAuth app installation flow
• file upload flows
• users., admin., or usergroups.* method families

Subscribe / Socket Mode Status

Slack inbound events can be delivered through Socket Mode. uxc now has a built-in Slack Socket Mode transport, but this skill still treats it as a limited event-ingest path rather than a fully packaged workflow surface.

Current uxc subscribe status:

• Slack Web API request/response calls are supported by this skill
• a live Socket Mode smoke test succeeded with the built-in transport:

- uxc subscribe start https://slack.com/api --transport slack-socket-mode --auth slack-app --sink file:... - the runtime opened a fresh temporary WebSocket URL automatically - the initial Slack hello frame was received

• a real inbound message event was validated end-to-end:

- while the Socket Mode job was running, a live Slack message event was delivered as an eventsapi envelope - the sink recorded the message payload and acksent=true

What the current built-in transport already handles:

• app-level xapp-... auth via --auth
• automatic apps.connections.open before each connect attempt
• raw Socket Mode frame capture
• automatic ack for envelopes that carry envelope_id

What is still not packaged:

• event-shape guidance per subscribed Slack event family
• higher-level workflow packaging for common Slack event intake flows

Slack Socket Mode is now a validated IM subscribe provider at the transport/runtime level.

Authentication

Slack Web API uses Authorization: Bearer <token>.

Token types used in practice:

• xoxb-...: Bot User OAuth Token. This is the recommended default for this skill.
• xoxp-...: User OAuth Token. Use this only when you explicitly want user-token semantics.
• xapp-...: App-level token. Use this for Socket Mode subscribe, not for normal Web API methods.

To create an app-level xapp-... token for Socket Mode:

1. Open the target Slack app at https://api.slack.com/apps
2. Go to Basic Information
3. Find App-Level Tokens
4. Generate a token with the connections:write scope
5. Enable Socket Mode in the app configuration before relying on subscribe-based event intake

Option 1: Bot Token (Recommended Default)

Use the Slack Bot User OAuth Token (xoxb-...) for the default binding and for most messaging operations:

uxc auth credential set slack-bot \
  --auth-type bearer \
  --secret-env SLACK_BOT_TOKEN

uxc auth binding add \
  --id slack-bot \
  --host slack.com \
  --path-prefix /api \
  --scheme https \
  --credential slack-bot \
  --priority 100

Option 2: User Token (Explicit Override For Selected Reads)

Use a separate Slack User OAuth Token (xoxp-...) when the method requires user-token semantics, especially thread/history access outside bot-accessible conversations:

uxc auth credential set slack-user \
  --auth-type bearer \
  --secret-env SLACK_USER_TOKEN

Do not bind slack-user by default to the same host/path. Invoke it explicitly when needed:

uxc auth binding match https://slack.com/api
slack-openapi-cli --auth slack-user get:/conversations.replies channel=C1234567890 ts=1717171717.000100

If you intentionally want writes to appear as the installing user rather than the bot, you can also invoke write methods with --auth slack-user, but treat that as an explicit override rather than the default path.

Core Workflow

1. Use the fixed link command by default:

- command -v slack-openapi-cli - If missing, create it: uxc link slack-openapi-cli https://slack.com/api --schema-url https://raw.githubusercontent.com/holon-run/uxc/main/skills/slack-openapi-skill/references/slack-web.openapi.json - slack-openapi-cli -h

1. Inspect operation schema first:

- slack-openapi-cli get:/auth.test -h - slack-openapi-cli get:/conversations.history -h - slack-openapi-cli post:/chat.postMessage -h

1. Prefer read validation before writes:

- slack-openapi-cli get:/auth.test - slack-openapi-cli get:/conversations.list limit=20 types=publicchannel,privatechannel - slack-openapi-cli get:/conversations.info channel=C1234567890

1. Execute with key/value or positional JSON:

- key/value: slack-openapi-cli get:/conversations.history channel=C1234567890 limit=20 - positional JSON: slack-openapi-cli post:/chat.postMessage '{"channel":"C1234567890","text":"Hello from UXC"}'

Operation Groups

Read / Lookup

• get:/auth.test
• get:/conversations.list
• get:/conversations.info
• get:/conversations.history
• get:/conversations.replies

Messaging / Reactions

• post:/chat.postMessage
• post:/reactions.add

Guardrails

• Keep automation on the JSON output envelope; do not use --text.
• Parse stable fields first: ok, kind, protocol, data, error.
• Bot token is the recommended default for send and basic read flows.
• Bot token means Slack Bot User OAuth Token (xoxb-...); do not confuse it with xapp-... app-level tokens.
• User token means Slack User OAuth Token (xoxp-...); use --auth slack-user when you intentionally need user identity or user-token-only reads.
• get:/conversations.replies has token-type restrictions:

- bot token works for IM and MPIM threads the bot can access - public/private channel thread reads should use --auth slack-user

• get:/conversations.history only returns conversations visible to the supplied token; a bot token is limited to joined conversations.
• Slack rate limits for conversations.history and conversations.replies vary by app distribution. Slack documents a tighter limit for newly created commercially distributed non-Marketplace apps starting on May 29, 2025; do not assume generic Tier 3 behavior.
• Treat post:/chat.postMessage and post:/reactions.add as write/high-risk operations; require explicit user confirmation before execution.
• slack-openapi-cli <operation> ... is equivalent to uxc https://slack.com/api --schema-url <slackopenapischema> <operation> ....

References

• Usage patterns: references/usage-patterns.md
• Curated OpenAPI schema: references/slack-web.openapi.json
• Slack Web API docs: https://docs.slack.dev/apis/web-api
• chat.postMessage: https://docs.slack.dev/reference/methods/chat.postMessage
• conversations.history: https://docs.slack.dev/reference/methods/conversations.history
• conversations.replies: https://docs.slack.dev/reference/methods/conversations.replies/