claude-esp: Watch Claude Code's Hidden Output in Real-Time

When working with Claude Code in the terminal, you spend a lot of time pressing Ctrl+O to peek at tool outputs and thinking. The collapsed interface keeps things tidy, but when you're debugging or just curious about what's happening under the hood, you want to see everything.

claude-esp is a small TUI that streams Claude Code's internal activity to a second terminal. It parses the JSONL files that Claude Code writes to ~/.claude/projects/ and displays thinking blocks, tool calls, and their results as they happen.

The Problem

Claude Code collapses tool outputs and thinking by default. This is sensible for a clean interface, but:

• You have to toggle visibility constantly when debugging
• You can't easily watch what a subagent is doing
• Scrolling back through collapsed history is tedious

The simple fix: run a watcher in a split pane that shows everything in real-time.

What It Shows

The TUI displays four types of content:

1. Thinking blocks - Claude's extended thinking (the <thinking> content)
2. Tool inputs - What tool was called and with what parameters
3. Tool outputs - The results that came back
4. Subagent activity - Any spawned Task agents and their operations
5. Background tasks - Tasks running in the background (⏳ running, ✓ complete)

Each item shows which agent generated it (Main or Agent-abc123), with visual indicators for active vs idle agents. Background tasks appear under the agent that spawned them - press Enter to load their output.

How It Works

Claude Code stores conversation transcripts as JSONL files:

~/.claude/projects/<project-path>/<session-id>.jsonl
~/.claude/projects/<project-path>/<session-id>/subagents/agent-<id>.jsonl

The watcher:

1. Discovers sessions modified in the last 5 minutes
2. Polls JSONL files every 500ms for new lines
3. Parses each JSON line looking for thinking, tool_use, and tool_result blocks
4. Renders them in a scrollable viewport with filtering controls

For long-running sessions, it auto-skips history (keeping only the last ~10 lines) so you're not buried in old output.

Usage

Run Claude Code in one terminal, claude-esp in another:

# Terminal 1
claude

# Terminal 2
claude-esp

It auto-discovers active sessions. If you have multiple sessions running, they all show up in the tree view on the left.

Flags

-s    Watch a specific session
-n        Skip history, live output only
-a        List active sessions
-l        List recent sessions

Keybindings

The TUI has filtering controls:

• t - Toggle thinking visibility
• i - Toggle tool input visibility
• o - Toggle tool output visibility
• a - Toggle auto-scroll
• h - Hide/show the session tree
• space - Toggle individual sessions/agents in tree

Navigation:

• j/k - Scroll or navigate
• g/G - Jump to top/bottom
• tab - Switch between tree and stream panes

Example tmux Setup

tmux new-session -s claude \\; \\
  split-window -h \\; \\
  send-keys 'claude-esp' C-m \\; \\
  select-pane -L \\; \\
  send-keys 'claude' C-m

This creates a side-by-side layout with Claude Code on the left and the watcher on the right.

Technical Notes

The parser handles Claude's message format, extracting content blocks from assistant messages and tool results from user messages. Tool inputs get formatted nicely - for Bash commands it shows the command, for Grep it shows the pattern, for Write it shows the file path and size.

Subagents are discovered dynamically. When Claude spawns a Task agent, the watcher notices the new JSONL file and starts tailing it.

The TUI is built with Bubbletea and Lipgloss. The viewport component handles scrolling, and the tree component handles session/agent selection.

Installation

git clone https://github.com/phiat/claude-esp.git
cd claude-esp
go build -o claude-esp .
./claude-esp

Why "ESP"?

It's a tool for seeing what Claude is "thinking" - extrasensory perception for your AI coding assistant.

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That's it. A small utility for a specific workflow need. If you spend time toggling Claude Code's output visibility, this might save you some keystrokes.