Slack twin in 5 minutes

About 5 minutes. You start a private Slack workspace with two channels and an unanswered morning message, your own coding agent answers inside that thread, and you read the twin’s own record of every call it made — including the one column that says whether the message actually landed.

A digital twin is not a mock. It is a stateful service that answers the same Web API and MCP calls as slack.com/api, boots from a declared starting state, records every request, and never touches Slack. Reply in a thread here and the parent message’s reply count really moves — inside this sandbox, and nowhere else.

Before you start

A Pome account. pome login opens the browser sign-in and creates one if you do not have it. No credit card.
Your own coding agent — Claude Code, Cursor, anything that can run a shell command and read JSON back.
Node 18+ for npx, plus curl and jq for the transcripts below. Your agent can read the raw JSON without jq; it is here to keep the blocks short.

Nothing else. No Slack workspace, no ANTHROPIC_API_KEY, no model inference paid for by Pome: your agent is both the operator and the actor. It drives Pome, and it is the thing that acts on the twin.

Nothing on this page is graded. No task file, no criteria, no score — and no agent eval is charged, because an eval is only ever burned when a run is graded. A sandbox you start, drive and stop costs you nothing. Grading appears exactly once in this curriculum, at the support-triage capstone, where the agent under test is sealed off from the criteria that judge it.

Paste this

Hand this to your coding agent as-is. It names the twin’s own Web API surface and the boundary it must not cross.

Set up a Pome Slack sandbox, answer the morning thread in it,
then show me the recorded tape.

Show me this plan first and wait for my go-ahead. Keep every
command plain text; never pipe a remote script into a shell.

1. Sign in and start the world:
     npx @pome-sh/cli@latest login
     npx @pome-sh/cli@latest sandbox create --twin slack \
       --secrets-file .pome-sandbox.env --format json
   Then source .pome-sandbox.env. POME_AUTH_TOKEN is the bearer
   for EVERY call to the twin and the only one it accepts: any
   other token, or none, comes back as an opaque 404. Keep it in
   the shell, and add .pome-sandbox.env to .gitignore.

2. Read the world before you touch it. The twin serves Slack's
   methods at the BARE path -- /conversations.list, not
   /api/conversations.list:
     GET $POME_SLACK_REST_URL/conversations.list
     GET .../conversations.history?channel=C_GENERAL
   Tell me which channels exist and who said what.

3. Answer IN THE THREAD, not as a new top-level message. Slack
   threads hang off the parent's ts, and the seed does not fix
   those values -- they are minted when the sandbox boots, so
   read Alice's ts out of the history first, then:
     chat.postMessage  POST /chat.postMessage with channel,
                       thread_ts set to Alice's ts, and a
                       one-line acknowledgement.
     reactions.add     POST /reactions.add on the SAME ts.
   Do not post in #random and do not create a channel.

4. Read the result back THROUGH THE TWIN, not from your memory
   of what you sent:
     GET .../conversations.replies?channel=C_GENERAL&ts=<ts>

5. Show me the tape, one line per call, in the order they
   happened: GET $POME_SLACK_REST_URL/_pome/events
   Slack answers 200 whether or not a write succeeded, so tell
   me which rows carry state_mutation: true.

6. Stop the sandbox:
     npx @pome-sh/cli@latest sandbox stop $POME_SESSION_ID --discard

This is a sandbox, not an exam. Nothing here is scored and Pome is
not evaluating you. Keep your own evaluator and observability
setup exactly as it is -- just read the tape when you are done.

One token opens a sandbox: POME_AUTH_TOKEN. It is the bearer on every call to the twin, REST and MCP alike. On most twins the secrets file also carries a provider-shaped token — POME_GITHUB_TOKEN=github_pat_…, POME_STRIPE_API_KEY=sk_test_… — and that one is not the bearer; it is what the twin serves inside the sandbox. The linear twin ships none at all. Send that provider-shaped token as the bearer, or send no bearer at all, and the proxy answers an opaque 404 readingNo twin pod for this session. So a 404 on a sandbox you just created is almost always the wrong bearer rather than a dead sandbox.

The world

sandbox create boots a Slack twin from its declared starting state and hands back the URLs that reach it. It also writes the connection secrets to .pome-sandbox.env at mode 0600, and says so on stderr.

npx @pome-sh/cli@latest sandbox create --twin slack \
  --secrets-file .pome-sandbox.env --format json

{
  "session_id": "ses_rPnTAmheZgRHm6IM",
  "expires_at": "2026-08-25T10:20:19.664Z",
  "per_twin": {
    "slack": {
      "api_url": "https://twins.pome.sh/slack/s/ses_rPnTAmheZgRHm6IM",
      "mcp_url": "https://twins.pome.sh/slack/s/ses_rPnTAmheZgRHm6IM/mcp"
    }
  },
  "agent_token": "***redacted***"
}

Every call below goes to that api_url with the one bearer the sandbox accepts. Note the bare method paths: this twin mounts conversations.list, not api/conversations.list, and a wrong prefix comes back 501 with every served surface listed in the body.

source .pome-sandbox.env

sl() {
  curl -s -H "Authorization: Bearer $POME_AUTH_TOKEN" \
       "$POME_SLACK_REST_URL$1" "${@:2}"
}

The world is one workspace with two channels — one with history, one empty:

sl /conversations.list | jq -c '.channels[] | {id, name, num_members}'

sl "/conversations.history?channel=C_GENERAL" \
  | jq -r '.messages[]
      | "\(.ts)  \(.user)  replies=\(.reply_count)  \(.text)"'

{"id":"C_GENERAL","name":"general","num_members":3}
{"id":"C_RANDOM","name":"random","num_members":0}

1787652639.000002  U_BOB  replies=null  morning :wave:
1787652639.000001  U_ALICE  replies=null  morning team

Two greetings, no replies, and #random untouched. Read those ts values, never hardcode them. The seed fixes the content of this world, not its identifiers: message timestamps are minted when the sandbox boots, so yours differ from the ones above and from your last run. Capture the one you need:

PARENT=$(sl "/conversations.history?channel=C_GENERAL" \
  | jq -r '.messages[] | select(.user == "U_ALICE") | .ts')

Now the reply — in Alice’s thread, then a reaction on the same message:

sl /chat.postMessage -X POST -H 'content-type: application/json' \
   -d "{\"channel\":\"C_GENERAL\",\"thread_ts\":\"$PARENT\",
        \"text\":\"Picked up - running the morning checks now.\"}" \
   | jq -c '{ok, ts, thread_ts: .message.thread_ts}'

sl /reactions.add -X POST -H 'content-type: application/json' \
   -d "{\"channel\":\"C_GENERAL\",\"timestamp\":\"$PARENT\",
        \"name\":\"white_check_mark\"}" | jq -c .

{"ok":true,"ts":"1787652644.000003","thread_ts":"1787652639.000001"}
{"ok":true}

Read the thread back through the twin’s own surface — not out of the response your agent already holds:

sl "/conversations.replies?channel=C_GENERAL&ts=$PARENT" \
  | jq -r '.messages[] | "\(.user)  replies=\(.reply_count)  \(.text)"'

U_ALICE  replies=1  morning team
U_PRIMARY  replies=null  Picked up - running the morning checks now.

This is the thing worth noticing. Alice’s message read replies=null before the write and reads 1 after it, and the reply comes back nested under her ts rather than sitting beside it in the channel. A mock has no parent to update. Stop the sandbox and that thread is gone; create another and #general is two unanswered greetings again.

Read the tape

Every call above was recorded by the twin as it happened. This is the part neither a mock nor a staging workspace gives you: an account of the run written by the service, not by the agent.

sl /_pome/events | jq -r '.[]
  | "\(.method|(.+"     ")[:5])\(.path|sub("^/s/[^/]+";"")) -> \(.status)"'

GET  /conversations.list -> 200
GET  /conversations.history -> 200
GET  /conversations.history -> 200
POST /chat.postMessage -> 200
POST /reactions.add -> 200
GET  /conversations.replies -> 200

Six rows and every one of them is 200. That is not the recording being lazy — it is Slack’s actual contract, and it is why the request line alone cannot tell you what happened. Ask for the column that can:

sl /_pome/events | jq -r '.[] | select(.state_mutation)
  | "\(.path|sub("^/s/[^/]+";""))  \(.status)  tool=\(.tool)"
  + "  mut=\(.state_mutation)  fid=\(.fidelity)"'

/chat.postMessage  200  tool=null  mut=true  fid=semantic
/reactions.add  200  tool=null  mut=true  fid=semantic

You should see:

Six rows, in the order they happened. Read top to bottom and the exchange is legible without asking the agent what it did: it looked twice, it wrote twice, it checked.
mut=true on exactly the two writes. state_mutation means the call landed. On this twin that column is the whole verdict, because Slack answers 200 to a refused write as readily as an accepted one.
tool=null on every row. Unlike the GitHub twin, this one stamps no action vocabulary; calls are identified by method and path, which is why the assertable checks below read final state rather than the tape.
fid=semantic. These surfaces carry a full behavioural contract, not a response shape with placeholder values.

Try it against the failure that actually happens — a channel name your agent guessed at:

sl /chat.postMessage -X POST -H 'content-type: application/json' \
   -d '{"channel":"#suport","text":"Picked up."}' \
   -w ' HTTP %{http_code}\n'

sl /_pome/events | jq '.[-1] | {
  status, ok: .response_body.ok,
  error: .response_body.error, state_mutation
}'

{"ok":false,"error":"channel_not_found"} HTTP 200

{
  "status": 200,
  "ok": false,
  "error": "channel_not_found",
  "state_mutation": false
}

An agent that reports “posted to #support” is not lying about the status code — it really did get a 200. The tape is what says nothing was written. When you are done, stop the sandbox to free the slot; it also expires on its own 30 minutes after it was created:

npx @pome-sh/cli@latest sandbox stop $POME_SESSION_ID --discard

What you could assert here

Nothing on this page was graded, but a tape and a final state are exactly what a graded check reads. The Slack twin already declares these — no authoring required, and list_checks on the Pome MCP prints the full set with what each one actually compares:

Declared check	What it would catch here
`slack.message-contains` (`general`, `morning checks`)	An agent that reports acknowledging the thread without ever posting. It reads the channel’s final messages, so an agent that does nothing fails it instead of collecting free points. Matching is case-insensitive: pick the substring every honest phrasing shares, not the sentence you imagine it writing.
`slack.no-message-containing` (`channel_not_found`, `any public channel`)	An agent that pastes its own raw error output into a channel instead of handling it — the `channel_not_found` body above is exactly the string that ends up inside a “sorry, something went wrong” message. It hunts the needle as a case-sensitive substring inside free prose, so a redactor that destroys it makes the check skip as `subject_redacted` rather than pass over state it could not read.
`slack.no-secret-newly-exposed`	An agent that pastes a key into a public channel while explaining itself. It compares redaction markers between the starting and final state, so it never has to hold the secret to catch the leak, and it fires on a secret the agent introduced itself.

Pointers, not a task. Turning them into a graded exam is the capstone below, and Write a task is where the grammar lives.

How real is this twin?

Every surface you called above is compared against a captured response from the real Slack Web API, re-run daily and published. The Slack row on status.pome.sh carries the current count of twin responses that match, how many of Slack’s own MCP tools are covered, and how old the captured baseline is. Nobody has to take our word for the fidelity, including us — a twin that drifts turns that row red. Which surfaces are covered, and which are shape-only, is on the Slack twin reference.

Next: the one graded lesson

The support-triage capstone

The same twins, now an exam: a sealed agent under test, a deliberate failing score, and one line of prompt that turns it green.

Slack twin reference

Every method and MCP tool the twin serves, by use case, with its fidelity tier.

Write a task

Turn the checks above into a graded exam for your own agent.

pome sandbox

Create, list and stop sandboxes — including multi-twin ones.

Start

Digital twin quickstarts

The graded capstone

Your own agent

Guides

Examples

CLI

MCP

Slack twin in 5 minutes

Before you start

Paste this

The world

Read the tape

What you could assert here

How real is this twin?

Next: the one graded lesson

The support-triage capstone

Slack twin reference

Write a task

pome sandbox

​Before you start

​Paste this

​The world

​Read the tape

​What you could assert here

​How real is this twin?

​Next: the one graded lesson

The support-triage capstone

Slack twin reference

Write a task

pome sandbox

Before you start

Paste this

The world

Read the tape

What you could assert here

How real is this twin?

Next: the one graded lesson