POST /v1/capsules/{id}/files/write — Upload a file

Use this endpoint to write a file to an absolute path inside a running capsule. The request uses multipart/form-data with two fields: the destination path and the file content. For files larger than a few megabytes, use the streaming variant to avoid buffering the entire payload in memory.

Endpoint

POST https://app.wrenn.dev/api/v1/capsules/{id}/files/write

Authentication

string

required

Your team’s API key. Pass the full wrn_... key value.

Path parameters

string

required

The ID of the capsule to write the file into. The capsule must be in the running state.

Request body

Content-Type: multipart/form-data

string

required

Absolute destination path inside the capsule filesystem, e.g. "/app/main.py". The parent directory must already exist.

binary

required

The file content to upload.

Example request

curl -X POST https://app.wrenn.dev/api/v1/capsules/cl-abc123/files/write \
  -H "X-API-Key: wrn_your_api_key_here" \
  -F "path=/app/main.py" \
  -F "file=@./main.py"

Response

Returns 204 No Content on success. No body is returned.

Streaming upload

For large files, use the streaming endpoint instead. It streams the payload directly to the capsule without buffering it in memory on the server:

POST https://app.wrenn.dev/api/v1/capsules/{id}/files/stream/write

The request format is identical — multipart/form-data with path and file fields. The response is also 204 No Content on success.

curl -X POST https://app.wrenn.dev/api/v1/capsules/cl-abc123/files/stream/write \
  -H "X-API-Key: wrn_your_api_key_here" \
  -F "path=/data/large-dataset.csv" \
  -F "file=@./large-dataset.csv"

Use the streaming endpoint for files larger than a few MB. The standard endpoint buffers the whole file before writing; the streaming endpoint does not.

Python SDK

from wrenn import Capsule

with Capsule(wait=True) as capsule:
    # Write a string directly
    capsule.files.write("/app/main.py", "print('hello world')")

    # Upload a file using the streaming endpoint (recommended for large files)
    def chunks():
        with open("large-dataset.csv", "rb") as f:
            while chunk := f.read(64 * 1024):
                yield chunk

    capsule.files.upload_stream("/data/large-dataset.csv", chunks())

Error responses

Status	Meaning
`409 Conflict`	The capsule is not in the `running` state. Resume or start the capsule first.
`413 Content Too Large`	The file exceeds the maximum allowed size. Use the streaming endpoint for large files.

Capsules

Execution

Files

Snapshots

POST /v1/capsules/{id}/files/write — Upload a file

Endpoint

Authentication

Path parameters

Request body

Example request

Response

Streaming upload

Python SDK

Error responses

​Endpoint

​Authentication

​Path parameters

​Request body

​Example request

​Response

​Streaming upload

​Python SDK

​Error responses

Endpoint

Authentication

Path parameters

Request body

Example request

Response

Streaming upload

Python SDK

Error responses