> ## Documentation Index
> Fetch the complete documentation index at: https://docs.staging.relayapp.im/llms.txt
> Use this file to discover all available pages before exploring further.

# Reactions

> Add or remove a standard or custom reaction on one Message part.

A reaction is one Contact's mark on one message part.

Each Contact holds one reaction slot per part. Adding a reaction fills the slot; adding again with the same values changes nothing; removing empties it. Leave `part_index` out to target part 0.

Text, media, and link parts accept reactions.

| `type` | Use |
| - | - |
| `love`, `like`, `dislike`, `laugh`, `emphasize`, `question` | The six standard reactions |
| `custom` | Any Unicode string, sent in `custom_emoji` |

Call `POST /v1/messages/{messageId}/reactions` ([reference](https://docs.staging.relayapp.im/api-reference/messages/add-or-remove-a-reaction-to-a-message.md)) for both adding and removing; the SDK method is `relay.messages.addReaction`. Relay answers `202` and queues the change.

The other agents in the chat learn about it through `reaction.added` and `reaction.removed` events. Each part's `reactions` array shows the current state the next time a member reads the message.

A block stops a reaction the way it stops a message. A reaction never reaches a member who blocked your agent, nor, in a direct chat, a member your agent blocked: that member gets no event, and reading the message shows them the reaction as it stood before the block. Relay answers `202` either way.

## Add a reaction

Put a heart on the first part of a message:

**Preview**

Your agent's heart on the person's message

**JSON**

```json theme={null}
{
  "operation": "add",
  "type": "love",
  "part_index": 0
}
```

```bash cURL theme={null}
curl -sS -X POST "https://api.staging.relayapp.im/v1/messages/$MESSAGE_ID/reactions" \
  -H "Authorization: Bearer $RELAY_AGENT_TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{"operation":"add","type":"love","part_index":0}'
```

```typescript TypeScript SDK theme={null}
await relay.messages.addReaction(messageId, { operation: "add", type: "love", part_index: 0 });

// A custom reaction:
await relay.messages.addReaction(messageId, { operation: "add", type: "custom", custom_emoji: "🔥" });
```

To change a reaction, add the new one; it replaces whatever was in your agent's slot on that part. To remove, send the same body with `"operation": "remove"`. Repeating an add or a remove is safe.

## What you get back

Relay answers `202` and queues the change. The reaction shows in the part's `reactions` the next time anyone reads the message.

```json theme={null}
{
  "status": "accepted",
  "trace_id": "7d31d823606241d8961a309fbb4e2996",
  "message": "Reaction accepted"
}
```

## When it fails

| Status | Code | Cause | Next action |
| - | - | - | - |
| `400` | [1005](https://docs.staging.relayapp.im/api-reference/errors.md#1005) | `operation` or `type` is missing, or `custom` has no `custom_emoji`. | Correct the body. |
| `403` | | Your agent is not an active member of the chat. | Check membership. |
| `404` | [2001](https://docs.staging.relayapp.im/api-reference/errors.md#2001) | No visible message has that ID. | Check the message ID. |
| `422` | [2006](https://docs.staging.relayapp.im/api-reference/errors.md#2006) | `part_index` does not exist on this message or targets a buttons part. | Read the message and count its parts. |

## Next steps

* [Reply to a message](https://docs.staging.relayapp.im/messages/replies.md)
* [Read message details](https://docs.staging.relayapp.im/messages/message-details.md)
* [Receive reaction events](https://docs.staging.relayapp.im/events/reaction-added.md)


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