Julia REPL — Behavioral Rules

Use the MCP tools (eval, reset, pkg, activate, session, revise, log_viewer, info) for interactive Julia work. Prefer julia script.jl via bash for one-shot scripts.

Before Every Eval

Always display code in a readable julia code block BEFORE calling eval. The MCP permission prompt shows code as an escaped string which is unreadable.

After Eval

MCP tool results are collapsed in Claude Code. For visual output (plots, heatmaps), tell the user to expand the tool result (Ctrl+O) to see it with full color — do NOT paste ANSI art into your message (it loses colors and streams token-by-token). For structured text (tables, matrices, DataFrames), paste in a fenced code block. Do not paste simple scalars or errors.

Revise vs Reset

Prefer revise — it preserves session state. Only reset when required.

Change	Action
Function/method body or signature	revise(action="revise")
Struct layout (Julia < 1.12)	reset required
Corrupted state / stuck code	reset required

After editing .jl files, call revise(action="revise") to hot-reload (the PostToolUse hook may do this automatically).

Error Recovery

Error	Fix
UndefVarError	Re-run definition or check spelling
MethodError	Check argument types
LoadError	pkg(action="add", packages="...")
cannot redefine	reset (struct layout change)
Hung/infinite	eval(code=..., timeout=5) or reset

First Use

On first Julia use in a conversation, ask which environment to activate (current directory, specific path, or global).

Capabilities

• Sessions persist variables, functions, and packages across evals
• Multiple named sessions provide isolated workers
• timeout parameter kills hung code and respawns the worker
• max_output prevents context overflow from large results
• isolated=true evals in a fresh module without polluting Main
• ephemeral=true evals in a disposable temporary session