{
  "query": "query listThreads($first: Int, $filters: ThreadsFilter) { threads(first: $first, filters: $filters) { edges { node { id externalId title status priority createdAt { iso8601 } customer { id fullName email { email } } assignedTo { ... on User { id fullName } ... on MachineUser { id fullName } } } } pageInfo { hasNextPage endCursor } } }",
  "variables": {
    "first": 20,
    "filters": {
      "statuses": ["TODO", "SNOOZED"]
    }
  }
}

Then run:

curl -s -X POST "https://core-api.uk.plain.com/graphql/v1" --header "Authorization: Bearer $PLAIN_TOKEN" --header "Content-Type: application/json" -d @/tmp/plain_request.json | jq '.data.threads.edges[].node | {id, title, status, customer: .customer.email.email}'

Get Thread by ID

Replace <thread-id> with the actual thread ID from the list threads response:

Write to /tmp/plain_request.json:

{
  "query": "query getThread($threadId: ID!) { thread(threadId: $threadId) { id externalId title status priority createdAt { iso8601 } updatedAt { iso8601 } customer { id fullName email { email } } assignedTo { ... on User { id fullName } ... on MachineUser { id fullName } } labels { id labelType { id name } } } }",
  "variables": {
    "threadId": "<thread-id>"
  }
}

Then run:

curl -s -X POST "https://core-api.uk.plain.com/graphql/v1" --header "Authorization: Bearer $PLAIN_TOKEN" --header "Content-Type: application/json" -d @/tmp/plain_request.json

Reply to Thread

Replace <thread-id> with the actual thread ID:

Write to /tmp/plain_request.json:

{
  "query": "mutation replyToThread($input: ReplyToThreadInput!) { replyToThread(input: $input) { timelineEntry { id timestamp { iso8601 } } error { message type code } } }",
  "variables": {
    "input": {
      "threadId": "<thread-id>",
      "textContent": "Thank you for reaching out. I'm looking into your issue and will follow up shortly."
    }
  }
}

Then run:

curl -s -X POST "https://core-api.uk.plain.com/graphql/v1" --header "Authorization: Bearer $PLAIN_TOKEN" --header "Content-Type: application/json" -d @/tmp/plain_request.json

Customers

Upsert Customer

Create a new customer or update an existing one by email:

Write to /tmp/plain_request.json:

{
  "query": "mutation upsertCustomer($input: UpsertCustomerInput!) { upsertCustomer(input: $input) { customer { id fullName email { email isVerified } externalId createdAt { iso8601 } } result error { message type code fields { field message type } } } }",
  "variables": {
    "input": {
      "identifier": {
        "emailAddress": "alice@example.com"
      },
      "onCreate": {
        "fullName": "Alice Thompson",
        "email": {
          "email": "alice@example.com",
          "isVerified": true
        },
        "externalId": "user_123"
      },
      "onUpdate": {
        "fullName": { "value": "Alice Thompson" }
      }
    }
  }
}

Then run:

curl -s -X POST "https://core-api.uk.plain.com/graphql/v1" --header "Authorization: Bearer $PLAIN_TOKEN" --header "Content-Type: application/json" -d @/tmp/plain_request.json

Get Customer by Email

Write to /tmp/plain_request.json:

{
  "query": "query getCustomerByEmail($email: String!) { customerByEmail(email: $email) { id fullName email { email isVerified } externalId createdAt { iso8601 } } }",
  "variables": {
    "email": "alice@example.com"
  }
}

Then run:

curl -s -X POST "https://core-api.uk.plain.com/graphql/v1" --header "Authorization: Bearer $PLAIN_TOKEN" --header "Content-Type: application/json" -d @/tmp/plain_request.json

Labels

List Label Types

Write to /tmp/plain_request.json:

{
  "query": "query listLabelTypes { labelTypes(first: 50) { edges { node { id name } } } }"
}

Then run:

curl -s -X POST "https://core-api.uk.plain.com/graphql/v1" --header "Authorization: Bearer $PLAIN_TOKEN" --header "Content-Type: application/json" -d @/tmp/plain_request.json | jq '.data.labelTypes.edges[].node | {id, name}'

Add Labels to Thread

Replace <thread-id> and <label-type-id> with actual values from the list threads and list label types responses:

Write to /tmp/plain_request.json:

{
  "query": "mutation addLabels($input: AddLabelsInput!) { addLabels(input: $input) { labels { id labelType { id name } } error { message type code } } }",
  "variables": {
    "input": {
      "threadId": "<thread-id>",
      "labelTypeIds": ["<label-type-id>"]
    }
  }
}

Then run:

curl -s -X POST "https://core-api.uk.plain.com/graphql/v1" --header "Authorization: Bearer $PLAIN_TOKEN" --header "Content-Type: application/json" -d @/tmp/plain_request.json

Error Handling

All mutations return an error field. Always check it — a 200 HTTP response can still contain an error:

{
  "data": {
    "replyToThread": {
      "timelineEntry": null,
      "error": {
        "message": "Thread not found",
        "type": "NOT_FOUND",
        "code": "thread_not_found"
      }
    }
  }
}

Guidelines

GraphQL only: All requests go to POST https://core-api.uk.plain.com/graphql/v1
Check error fields: Mutations return errors in the response body, not via HTTP status codes
Pagination: Use Relay-style cursor pagination — pass first and after (from pageInfo.endCursor) for subsequent pages
Machine User permissions: Grant the minimum permissions needed (e.g., threads:read, customers:write)
Thread statuses: TODO (needs action), SNOOZED (waiting), DONE (resolved)
Full schema: Available at https://core-api.uk.plain.com/graphql/v1/schema.graphql

API Reference

GraphQL endpoint: https://core-api.uk.plain.com/graphql/v1
Schema: https://core-api.uk.plain.com/graphql/v1/schema.graphql
Documentation: https://www.plain.com/docs/graphql/introduction

plain

Troubleshooting

Threads

List Threads