Known differences

Slack

A Slack workspace that answers the Web API, Events API, Socket Mode and interactivity flows slack_sdk and Bolt use, plus an MCP server.

Vendor reference: https://api.slack.com/methods ↗. Machine-readable: compat/slack.json.

Surfaces

Kind	Path	Notes
REST	`/api/<method>`	the Web API; an unknown method answers 404 `unknown_method`
Streaming	`apps.connections.open`	Socket Mode WebSocket with an `xapp-` app-level token
Webhooks	`Events API`	event callbacks and interactivity payloads delivered to your app
OAuth	`oauth.v2.access`	bot and user tokens, and Sign in with Slack (`openid.connect.*`)
MCP	`/mcp`	Slack MCP tools over the same workspace

API versions: Web API (unversioned methods)

Supported

Users, conversations, history, replies, members, chat, reactions, pins, bookmarks, usergroups and views
The files_upload_v2 external upload flow, file info and downloads; files.upload answers method_deprecated
search.messages, search.files and search.all with the operators in:, from:, after:, before:, on: and during:
Socket Mode with slack_sdk's SocketModeClient, the Events API and interactivity
The official Python SDK, documented in its own matrix
SCIM and the Audit Logs API for the one workspace a tenant models

Not supported

Enterprise Grid, cross-team installs and admin.* methods
Slack Connect with a second real org; shared channels are with synthetic partner orgs
Methods the SDK documents but the replica does not simulate

Known differences and test guidance

Scenario	Difference from Slack	In your tests
Search ranking	Search is substring matching over the workspace, not Slack's ranked index; `score` and highlighting are approximations.	Assert that the expected message is in the results, not on its rank or score.
Rate limits	Nothing throttles on its own; a 429 only happens when you inject one.	Do not expect organic tier limits. Inject `throttle` or `fail_next` to test retry handling.
Human activity	Nobody clicks buttons, votes or replies unless you inject the event or interaction.	Drive interactions yourself; do not wait for a user response.
File contents	Text, Markdown and CSV bodies are generated from the document's title, folder and owner, not original bytes.	Assert on file metadata and format, not on content.
Canvases, polls, assistant threads, streaming replies, link unfurls	Canvases are markdown sections; polls are ordinary messages with poll blocks; assistant status and streamed text are stored but not rendered; `chat.unfurl` stores what the app sends and nothing fetches links.	Assert on what the API returns, not on client rendering or automatic unfurls.
Timestamps on writes	A message you post is stamped from the host clock, which can fall after the seeded history unless the workspace runs on today's date.	Do not assert that new messages sort before or among the seeded history.
Restarts	Without a state directory the workspace lives in memory and a restart drops writes.	Treat each run as starting from the seeded workspace.
Request size	A Web API body over 8 MiB is refused with HTTP 413; Slack documents per-argument limits instead.	Do not test large-body behaviour against the replica.

Fault injection

Key	What the client sees
`throttle`	429 with `Retry-After` and `{"ok": false, "error": "ratelimited"}`, which `slack_sdk` retries on
`fail_next`	The next N calls fail as `throttle` does, then clear
`quota_limit`	429 `ratelimited`, the same shape as `throttle`
`error_rate`	500 `{"ok": false, "error": "internal_error"}` for the given fraction of calls
`latency_ms`	Fixed added latency on every data-plane request

Applies to every system

The hosted data plane is read-only: a write is refused with 403 writes_disabled. A SOQL, GraphQL or search POST is a read and is answered.
Faults are injected through POST /_admin/faults on a simulator you run yourself; POST /_admin/faults/reset clears them.
Rate limits do not happen on their own unless a page says so. Use fault injection to exercise a client's backoff.
Distributions come from aggregated metadata sketches of data Eon backs up; no customer records; all Era data is simulated.