Prompt Mode and Prefixes — Claude Code Training

The Three Prompt Modes

Claude Code has three operating modes. Each one defines what Claude is allowed to do during a session.

You start every session in Default mode. The other two are opt-in — activated when the situation calls for them.

Default Mode

Default mode is the starting point for every session. Claude can read files, write files, run commands, and act on its own judgment.

There is nothing to configure — you are already in Default mode the moment you open Claude Code.

Tip

Default mode is appropriate for most tasks. Use the other modes only in specific situations, not as a habit.

Plan Mode

Plan mode removes the ability to act. Claude can read and reason freely, but it will not edit any file or run any command. It describes what it would do instead.

When to use it:

Before a large refactor you have not fully mapped out
When touching code you do not fully understand
Any time you want to review an approach before anything changes

Activate: Shift+Tab twice, or type /plan — Exit: Shift+Tab once, or /plan again

Tip

Plan mode costs nothing and can save you from a bad refactor. Run it first on any task that touches unfamiliar files, then switch back once you are satisfied with the plan.

Accept Edits Mode

Accept edits mode does the opposite of Plan mode. Claude applies file edits automatically, without stopping to ask for confirmation on each change.

When to use it:

After reviewing a plan — you understand what will happen
When running a batch of changes without interruption

Activate: Shift+Tab once from Default mode — Exit: Shift+Tab once to return to Default mode

Warning

Only use Accept edits mode after reviewing a plan first. Changes apply immediately — there is no confirmation prompt to catch mistakes.

The Input Prefixes

Prefixes are single characters you place immediately before a word. Each one changes how Claude Code interprets that input.

Prefix	Name	What it does
`@`	File reference	Include a file or directory in context
`!`	Shell command	Run a command and pass its output to Claude
`&`	Background task	Run a command in the background while Claude continues
`#`	Comment	Record a note in the session log without sending it to Claude

Prefixes work in both interactive and non-interactive sessions, and you can combine more than one in the same message.

@ — File Reference

The @ prefix includes a specific file or directory in Claude’s context for that message. Without it, Claude may read several files to orient itself. With it, you point directly to what is relevant.

# Include a single file
> @src/model.py explain the forward pass

# Include multiple files at once
> @src/preprocessing.py @tests/test_preprocessing.py the test is failing — why?

This reduces token usage and focuses Claude on the relevant code. In a large project with dozens of modules, you will see fewer unnecessary file reads.

! — Shell Command

The ! prefix enters bash mode — the input is run directly as a shell command, without Claude interpreting it. The command output is added to the conversation context. You then ask Claude about it in the next message.

# Step 1: run the command
! pytest tests/test_model.py -v

# Step 2: ask Claude about the output
> what is causing the assertion error in test_predict?

# Step 1: add the git log to context
! git log --oneline -10

# Step 2: ask Claude to reason about it
> which of these commits is most likely to have introduced the regression?

This is particularly useful for data scientists: run a training job output, a dataset shape check, or a notebook cell result, then ask Claude about it without leaving the session.

& — Background Task

The & prefix runs a command in the background. Claude Code returns a background task ID immediately and can continue responding to prompts while the command executes.

# Start a long training run in the background
> & python src/train.py --config configs/default.yaml

# Continue working while it runs
> @src/evaluate.py review the evaluation logic while the training runs

Use it for anything slow — training jobs, test suites, data pipelines — where waiting is just wasted time.

# — Comment

The # prefix records your input in the session log without sending it to Claude as a prompt. Claude does not respond to it.

Use it to leave a note mid-session without breaking your flow:

# Trying the sklearn approach first — may switch to custom transformer if it fails
> @src/features/transform.py refactor the imputation step to use ColumnTransformer

The comment stays visible in your session history as a reference for yourself, while Claude proceeds as if it wasn’t there.

Combining Prefixes

The prefixes complement each other within the same session. Use them in sequence to build up the context Claude needs before asking your question.

# Add a file to context
> @src/train.py

# Run a command to get its output into context
! python -c "import src.train; print(src.train.__version__)"

# Now ask Claude with full context available
> does the version in the file match what Python reports?

By the time you ask the question, Claude has the file and the command output in context.