Slack

Lightweight, dependency-free, in-memory fake of the Slack Web API for testing code that uses the real @slack/web-api WebClient (and the language-agnostic Slack Web API).

Default port: 4654

Quick start

Start the server:

import { SlackServer } from "./services/slack/src/server.js";

const server = new SlackServer(4654);
await server.start();
// ... run your app/tests ...
await server.stop();

Point the real @slack/web-api client at it. The WebClient reads its base URL from the slackApiUrl option, so override it to the parlel fake:

import { WebClient } from "@slack/web-api";

const web = new WebClient("xoxb-parlel-test-token", {
  slackApiUrl: "http://127.0.0.1:4654/api/", // point at the parlel fake
});

const res = await web.chat.postMessage({
  channel: "C_GENERAL1",
  text: "hello from parlel",
});
// res.ok === true, res.ts === "<seconds>.<micros>", res.channel === "C_GENERAL1"

const history = await web.conversations.history({ channel: "C_GENERAL1" });
// history.messages[0].text === "hello from parlel"

Every posted message, channel, file, reaction, etc. is captured in memory and can be inspected via the /__parlel/* endpoints (see below). The whole world is resettable.

Wire protocol

The fake speaks the exact Slack Web API wire protocol that @slack/web-api uses:

• Every method is a POST (GET also accepted) to /api/<method> — e.g. POST /api/chat.postMessage.
• The request body is application/x-www-form-urlencoded (the SDK default) or application/json. Nested values (blocks, attachments, view, files, profile) may be JSON-encoded strings, which the fake parses transparently.
• The token is supplied via the Authorization: Bearer xoxb-... header or a token body param.
• Responses are always HTTP 200 with a JSON body { "ok": true, ... } on success or { "ok": false, "error": "<code>" } on failure (Slack does not use non-2xx status codes for application errors). @slack/web-api throws an error with code === "slack_webapi_platform_error" and error.data.error === "<code>" when ok is false.

Implemented operations

Auth & misc

• api.test — echoes args (no auth required); returns the provided error if set
• auth.test — bot/team identity
• auth.revoke — revoke the current token (test=true is a no-op probe)
• team.info
• emoji.list

chat

• chat.postMessage — supports text, blocks, attachments, thread_ts, reply_broadcast, username. Bot-token posts return message.subtype === "bot_message" with a username and bot_id, exactly like the real API.
• chat.postEphemeral
• chat.update
• chat.delete
• chat.meMessage
• chat.getPermalink
• chat.scheduleMessage
• chat.deleteScheduledMessage
• chat.scheduledMessages.list

conversations

• conversations.list — returns channel objects with the full standard field set (is_member, is_shared, is_ext_shared, is_org_shared, unlinked, pending_shared, is_pending_ext_shared, previous_names)
• conversations.create — granular name validation (invalid_name_required, invalid_name_maxlength, invalid_name_specials, invalid_name_punctuation)
• conversations.info
• conversations.history
• conversations.replies
• conversations.members
• conversations.join
• conversations.leave
• conversations.open (DM + multi-party IM)
• conversations.invite
• conversations.kick
• conversations.rename
• conversations.setTopic
• conversations.setPurpose
• conversations.archive
• conversations.unarchive
• conversations.mark

users

• users.list
• users.info
• users.lookupByEmail
• users.identity
• users.setPresence
• users.getPresence
• users.conversations
• users.profile.get
• users.profile.set

reactions

• reactions.add
• reactions.remove
• reactions.get
• reactions.list

pins

• pins.add
• pins.remove
• pins.list

bookmarks

• bookmarks.add
• bookmarks.list
• bookmarks.edit
• bookmarks.remove

files

• files.upload (legacy; supports content, channels, initial_comment)
• files.info
• files.list
• files.delete
• files.getUploadURLExternal + files.completeUploadExternal (the modern files.uploadV2 two-step flow)

views (Block Kit surfaces)

• views.open
• views.push
• views.publish (App Home)
• views.update

usergroups

• usergroups.create
• usergroups.list
• usergroups.update
• usergroups.users.list
• usergroups.users.update

parlel control / inspection endpoints

These are not part of Slack — they are parlel extensions for test setup and assertions.

Default seeded state

After start() (or reset) the world contains:

• Workspace T_PARLEL01 ("Parlel Workspace", domain parlel)
• Bot user U_BOT00001 (parlelbot, bot_id B_BOT00001)
• Admin user U_ALICE001 (alice, alice@parlel.test)
• Channels C_GENERAL1 (#general) and C_RANDOM01 (#random)
• Accepted tokens: xoxb-parlel-test-token, xoxp-parlel-test-token, xapp-parlel-test-token

Surface coverage

This emulator faithfully replicates the API surface most application code and agents exercise. Anything below the supported lines is either an intentional design choice for a fast, zero-cost local emulator (✓ By design) or a candidate for a future release (⟳ Roadmap) — never a silent inaccuracy.

Legend: ✅ fully supported · ◐ accepted (stored, not strictly enforced) · ✓ by design · ⟳ on the roadmap.

Error codes / shapes

All errors are returned as HTTP 200 with { "ok": false, "error": "<code>" }. Common codes:

The image target stays tiny (<1MB): a single pure-Node.js file, no external npm dependencies.

Configuration — test.env

Copy these into your test.env (used by the bridge sidecar flow). Tokens are Parlel's seeded test credentials — any non-empty value is accepted by the emulator, so you rarely need to change them. Swap in real credentials only when pointing at the live service in prod.env.

SLACK_BOT_TOKEN=xoxb-parlel-test-token
SLACK_APP_TOKEN=xapp-parlel-test-token
SLACK_SIGNING_SECRET=parlel_test_signing_secret
SLACK_BASE_URL=http://parlel-bridge:4654/api/