Run an agent that iterates on a config file

An agent running on the core edits your config in place — in an isolated sandbox, verifying every change as it goes.

You have a config file. You want the agent to tweak it — change one value, add a section, refactor the structure. You don't want to copy-paste into a chat window over and over.

The flow

1. Upload the config (via upload.create_link or upload.write, whichever fits the size).
2. Tell the agent what to change. Agent edits in place via sh.
3. Verify with sh "cat" (or diff).
4. Once happy, retrieve the new version (see the download story — small text is fine via sh; bigger configs need the workaround until the native download surface ships).

A worked example

You drop next.config.mjs at /workspace/next.config.mjs. Then:

> Add server-side externalisation for @aws-sdk packages.

Agent runs:

sh "cat /workspace/next.config.mjs"     # read current state
sh "cat > /workspace/next.config.mjs <<'EOF'
... updated content ...
EOF"
sh "cat /workspace/next.config.mjs"     # verify

Or for surgical edits:

sh "sed -i 's/serverExternalPackages: \\[/serverExternalPackages: [\"@aws-sdk\\/client-s3\", /' /workspace/next.config.mjs"

Why this is powerful

• Real, persistent state. Unlike paste-in-chat, the file lives somewhere — across turns, across conversations, across machines.
• The agent can diff. sh "diff" against a backup, against your local version, against a known-good template.
• You can roll back. Keep a backup at /workspace/configs/backup/ and overwrite from it when an edit goes wrong.

Subtle: no undo

Once sh "cat > foo" runs, the previous content is gone. R2 keeps no version history. If you want safety, snapshot first:

sh "cp /workspace/next.config.mjs /workspace/configs/backup/next.config.$(date +%s).mjs"

Then ask the agent to edit. If you don't like the result:

sh "cp /workspace/configs/backup/next.config.<timestamp>.mjs /workspace/next.config.mjs"

When to use upload.write vs sh for edits

• Total rewrite, content is small (< 1 MiB): upload.write with content_text. Cleaner than a heredoc.
• Surgical edit, content is large: sh "sed" or sh "awk". Don't re-upload the whole file just to change one line.
• Format-preserving edits to JSON/YAML/TOML: sh "yq" / sh "jq". They're available in the default sandbox image.

Next steps

• Generate a starter project from a template.
• Today — get a file out of /workspace.

Where this fits

This is the Run your agents pillar of connect0 — the core that connects everything your company runs on. The agent runs on the core against real, persistent files in your workspace — editing, diffing and rolling back in an isolated sandbox instead of copy-pasting into a chat window. Start building → · All guides →