# Reply in a thread **POST /threads/{thread}/messages** Posts a reply in a thread and returns it. Needs `content: write`, and is a write. The reply is written by the person the credential belongs to, and the people in the thread are notified the way they are for any reply. It needs `content`, `media`, or both. Leave `parent` out to reply to the thread itself. Name a reply in `parent` to reply to it: a conversation is two levels deep, so the parent has to be a direct reply to the thread, and a reply to a reply to a reply answers `422`. `quoted` optionally quotes the thread or any message in it. Both take a message's `id` or `short_id`, and both have to be in this thread. A reply has no visibility of its own: it is exactly as readable as its thread. A locked thread takes no replies and answers `409`. Publishes `message.created`. ## Servers - Production. There is no separate sandbox host. : https://api.usecommune.com (Production. There is no separate sandbox host. ) ## Authentication methods - Api key - Oauth2 ## Parameters ### Headers - **Idempotency-Key** (string) A value of your choosing naming the change this request is making. Send the same value again to retry the same request. Commune replays the answer the first attempt gave instead of making the change twice, and marks the replay with an `Idempotent-Replay: true` response header. Send a different value for a different change: a key reused for a request that differs in any way answers `409`, because replaying an answer to a question you did not ask is a wrong answer you could not detect. A UUID per change is the usual choice. Remembered for 24 hours, per credential, so two credentials choosing the same value never see each other's answers. Required, not optional. - **Commune-Version** (string) The contract version this request is written against. Every version published so far is a release date (`YYYY-MM-DD`), which is why the examples look like one, but the value is an opaque identifier: match it against the versions this API publishes rather than parsing it, because a future one may not be only a date. An unknown value answers `400` with `invalid_version`. Omitting the header pins the request to the version that was current when the API key was issued, so an integration keeps working when a newer version ships. ### Path parameters - **thread** (string) The thread's `id` (a UUID) or its `short_id`. A thread that Commune opened under an article has no `short_id`, because it is addressed on the web through the article's own permalink, so use its `id`. ### Body: application/json (object) - **content** (string) The reply, as Markdown. Surrounding whitespace is trimmed. Optional when `media` attaches something: a post needs text, attachments, or both. - **parent** (string) The reply this answers, by `id` or `short_id`. Leave it out to reply to the thread itself. It has to be a direct reply to this thread. - **quoted** (string) The thread or a message in it to quote, by `id` or `short_id`. - **media** (array[object]) Images or videos to attach, by URL. ## Responses ### 201 The reply, as created. #### Body: application/json (object) - **object** (string) Always `message`. - **id** (string(uuid)) Stable identifier. - **short_id** (string | null) Eight character base62 identifier used by the message's permalink. Null for a message old enough that none was assigned. - **thread** (object | null) The thread this reply belongs to. A `Ref` unless `thread` is named in `?expand=`. - **newsletter** (object | null) The community the thread lives in, denormalised so a client does not have to walk up to it. A `Ref` unless `newsletter` is named in `?expand=`. - **author** (object | null) Who wrote the reply. A `Ref` unless `author` is named in `?expand=`. - **parent** (object | null) The message this one replies to, or `null` when it replies to the thread itself. A `Ref` unless `parent` is named in `?expand=`. - **quoted** (object | null) The message this one quotes, when the author quoted rather than replied. `null` otherwise. A `Ref` unless `quoted` is named in `?expand=`. - **depth** (integer) `1` for a reply to the thread, `2` for a reply to a reply. Commune does not nest deeper, so a client can render the tree with a fixed two level layout. - **content** (string) The message body as HTML. Treat it as untrusted markup and render it in a sandboxed context. - **media** (array[object]) Attachments on the message. - **highlight** (object | null) The passage of an article this reply is anchored to, when the reader wrote it from a highlight. `null` otherwise. A `Ref` unless `highlight` is named in `?expand=`. - **created_at** (string(date-time)) When the reply was written. - **updated_at** (string(date-time)) When the row last changed for any reason. - **edited_at** (string(date-time) | null) When the author last edited the text or attachments. Not touched by reactions or other side effects, so it is a faithful edited marker. - **reactions** (array[object]) The emoji reactions on this message, one entry per distinct emoji, most used first. Empty when there are none. Each entry carries `users`, who left it, only when `reactions` is named in `?expand=`. ### 400 The request was malformed, and the same request will fail the same way until it is changed. `param` names the parameter or header at fault when there is exactly one, and `allowed_values` lists what it accepts when that is a finite set. The code is `bad_request` for every case below except the last. * **A query parameter**: one the operation does not have, a value outside its set, range or format (an unparseable cursor, an unknown `expand` path or `fields` name, an identifier that is not a UUID), or a required one left out, such as `q` on a search or `newsletter` when the credential reaches more than one. * **The request body**: not JSON, not the shape the operation reads, a property it does not write, or a value of the wrong type, length or format. `param` is absent here, since the body is not a parameter, and the message names the property. * **The `Idempotency-Key` header**, on an operation that changes something: missing, or a value this API will not store. * **An unrecognised `Commune-Version`**, which answers with its own code, `invalid_version`, because it is never fixed by changing the body. #### Body: application/json (object) - **error** (object) ### 401 No credential was presented, or it is malformed, unknown, revoked or expired, or it is an access token minted for a different audience. Every one of these answers identically, down to the wording and the headers, so a refusal never confirms that a string was once real. #### Headers - **WWW-Authenticate** (string) The authentication scheme this API accepts, and where to find out how to get a credential for it. Always `Bearer realm="Commune API", resource_metadata="https://api.usecommune.com/.well-known/oauth-protected-resource"`. `resource_metadata` is the RFC 9728 pointer to this API's protected resource metadata, which names the authorization server an OAuth client should send its user to. A client holding an API key can ignore it. The header carries no `error` parameter, not even `error="invalid_token"`, because it describes what this API accepts rather than what was wrong with the credential sent, and the reasons above are deliberately indistinguishable. There is no second scheme and no query-parameter fallback, because a credential that can travel in a URL ends up in access logs and referer headers. #### Body: application/json (object) - **error** (object) ### 402 The credential is allowed to do this but the newsletter's plan does not include it. Two surfaces can answer it: **insights**, the engagement and metrics operations, which are the only reads Commune reserves the right to meter, and **writing**, every operation that changes something. Every other read stays free on every plan, so a credential refused at one of these can still read everything else. The body names the plan the newsletter is on and the plans that would work. **This status is predictable and should not be how you discover it.** `GET /newsletters/{newsletter}/entitlements` answers the same question in advance, carrying the same plan list this puts in `allowed_values` and the same sentence it puts in `message`. Read it once at the start of a run rather than finding out in the middle of one. #### Body: application/json (object) - **error** (object) ### 403 The credential is valid but is not allowed to do this. Two codes answer with this status, and `error.code` says which. **`insufficient_scope`: it does not hold the permission.** The operation needs, say, `audience: read` on the newsletter addressed, and this credential holds less than that there. `allowed_values` carries the permission that was needed, and the message says what the credential does hold on that newsletter, because a credential granted the wrong family and a credential belonging to somebody whose standing on the team has narrowed look identical without it. The answer can differ per newsletter: the same credential may be allowed here and refused on the next one it reaches. The same code answers an operation that needs the **account permission** from a credential that does not carry it. That permission is about the person a credential belongs to rather than about any newsletter, so nothing granted on a newsletter adds up to it. It is granted on the credential itself, when a key is minted or when an authorization asks for `account:read`. And it answers a parameter the credential may send, but not with the value it sent: a filter a credential holding only `read` permissions may not use, or an `expand` path whose rows need a permission the operation does not. `param` names the parameter, and `allowed_values` carries what this credential may send instead, or is absent when it may send nothing there at all. **`forbidden`: it may not act here at all.** Either the credential does not reach the newsletter addressed, because it was never granted it or because the person it belongs to can no longer act on it, or it reaches no newsletter at all; `param` is `newsletter`, and `GET /newsletters` lists the ones it does reach. Or, on `DELETE /api-keys/{key}`, the credential named belongs to somebody else. Neither carries `allowed_values`, because there is no value to send instead. #### Body: application/json (object) - **error** (object) ### 404 No such resource, or the key is not allowed to know that it exists. Commune answers `404` rather than `403` where distinguishing the two would leak the existence of private content. #### Body: application/json (object) - **error** (object) ### 409 The request collided with something. On a write this is always the `Idempotency-Key`, in one of two ways, and the message says which. Either the key was already used for a **different** request, which is refused rather than answered with the earlier request's result. Or an earlier request using the same key has not finished, or never reported an outcome, in which case this one was not run and the key becomes usable again shortly. Nothing was changed by a request that answers this. #### Headers - **Retry-After** (integer) Seconds to wait before retrying, on the second case only. #### Body: application/json (object) - **error** (object) ### 422 The request is well formed and every value in it is legal, and the state of what it addresses refuses it anyway. The message says what about that state is in the way. #### Body: application/json (object) - **error** (object) ### 429 Too many requests. Back off and retry after the interval named by the `Retry-After` response header. One of the budgets in `RateLimit-Policy` ran out, and the `RateLimit-*` headers on this response say which and when it resets. #### Headers - **Retry-After** (integer) Seconds to wait before retrying. #### Body: application/json (object) - **error** (object) ### 500 Something failed inside Commune. The request may be retried. #### Body: application/json (object) - **error** (object) [Powered by Bump.sh](https://bump.sh)