devtap

Bridge build/dev process output to AI coding sessions automatically.

devtap captures stdout/stderr from build and development commands, then feeds them into AI coding tool sessions via MCP (Model Context Protocol). It can also fan out the same output to multiple coding agents. Each agent drains its own copy so parallel sessions don't interfere.

The Problem

In vibe coding workflows, you run an AI coding tool in one terminal and build commands in another. When errors occur, you manually copy-paste logs into the coding session. devtap automates this feedback loop.

Three common cases make this especially painful:

1. Multiple local dev processes (frontend + backend + worker) that you need to keep an eye on and fix quickly.
2. Multiple coding agents working on the same project, where you want them to analyze the same failures in parallel and compare findings.
3. Build/test runs on remote machines (CI, dev boxes) whose output you need to feed back to a local coding agent.

Quick Start

Install

go install github.com/killme2008/devtap/cmd/devtap@latest

Or install via Homebrew:

brew install killme2008/tap/devtap

Or download from GitHub Releases.

Setup

cd /path/to/your-project
devtap install --adapter claude-code

This configures the MCP server and injects devtap instructions into your project's instruction file (e.g., CLAUDE.md). See Supported Tools for all available adapters.

Skills (Optional)

devtap ships with a built-in skill that works as a CLI fallback when MCP is unavailable. Install it to let the agent fetch build output on demand:

# Claude Code
mkdir -p ~/.claude/skills && cp -r skills/devtap-get-build-errors ~/.claude/skills/

# Codex CLI
mkdir -p ~/.codex/skills && cp -r skills/devtap-get-build-errors ~/.codex/skills/

Or fetch directly from the repo without cloning:

DEST=~/.claude/skills/devtap-get-build-errors
mkdir -p "$DEST" && cd "$DEST"
for f in SKILL.md scripts/get_build_errors.sh; do
  mkdir -p "$(dirname "$f")"
  curl -sL "https://raw.githubusercontent.com/killme2008/devtap/main/skills/devtap-get-build-errors/$f" -o "$f"
done
chmod +x scripts/get_build_errors.sh

Usage

Terminal A — capture build output:

devtap -- cargo check
devtap -- go build ./...
devtap --filter-regex "error|warning" -- npm run build

# Long-running dev servers (output is flushed every 2s by default)
devtap -- npm run dev

Terminal B — use your AI coding tool as usual. It will automatically call get_build_errors via MCP to fetch captured build errors.

If you want to verify without MCP, run:

devtap drain

Typical output:

[devtap: cargo check] Build failed (exit code 101):
...

Tip: Since devtap captures stdout from any command, you can send arbitrary messages to your coding agent:

devtap -- echo "Please refactor the auth module to use JWT"

This turns devtap into a general-purpose human→agent message channel — no copy-paste needed.

How It Works

Local mode (default, file-based):

Terminal A (Claude Code)          Terminal B (build/dev)
┌──────────────────┐             ┌────────────────────────────┐
│  MCP tool call:  │   stdio     │  devtap -- cargo check     │
│  get_build_errors├─────────────┤                            │
│                  │  JSON-RPC   │  captures stdout/stderr,   │
│  receives errors,│             │  fans out to all adapters: │
│  fixes code      │             │  ~/.devtap/<s>/claude-code/│
└──────────────────┘             │  ~/.devtap/<s>/codex/      │
                                 └────────────────────────────┘

Cross-machine mode (with GreptimeDB):

Your laptop                       CI / remote build server
┌──────────────────┐             ┌────────────────────────────┐
│  Claude Code     │             │  devtap -- make            │
│  get_build_errors│             │                            │
│                  │             │  captures stdout/stderr    │
│  receives errors,│             └─────────────┬──────────────┘
│  fixes code      │                           │ write
└────────┬─────────┘                           ▼
         │ drain              ┌────────────────────────────┐
         └───────────────────►│        GreptimeDB          │
                              │  (shared session store)    │
                              └────────────────────────────┘

1. devtap install configures the MCP server for your AI tool (pass --session and --store for cross-machine setup)
2. devtap -- <cmd> runs your command, captures stdout/stderr, fans out to all registered adapters
3. Each AI tool independently drains its own copy via get_build_errors
4. AI sees the errors and fixes them

When mcp-serve/drain is started with explicit --session or --store, devtap can merge output from two sources:

• local: auto-detected project session from your default backend
• configured: the explicit --session/--store target

If both resolve to the same backend+session, devtap uses a single source. Otherwise it drains both, deduplicates identical messages, and prefixes tags with source info (for example myhost/local |).

Supported Tools

Tool	Adapter	Integration	Config File	Instruction File
Claude Code	claude-code	MCP server	.mcp.json	CLAUDE.md
Codex CLI	codex	MCP server	.codex/config.toml	AGENTS.md
OpenCode	opencode	MCP server	opencode.json	AGENTS.md
Gemini CLI	gemini	MCP server	.gemini/settings.json	GEMINI.md
aider	aider	--lint-cmd wrapper	.devtap-aider-lint.sh	CONVENTIONS.md

Any MCP-compatible tool can use devtap mcp-serve directly.

Auto-loop Mode (Claude Code)

Claude Code supports a Stop hook that can block Claude from stopping when errors remain:

devtap install --adapter claude-code --auto-loop --max-retries 5

This configures:

• MCP server for on-demand error queries
• Stop hook that blocks Claude from finishing if build errors are pending
• Safety limit of 5 retries before allowing stop

Storage Backends

File (default)

Zero-dependency JSONL files at ~/.devtap/<session>/<adapter>/pending.jsonl. Each adapter gets its own queue for independent consumption. Atomic rename for concurrency safety.

GreptimeDB (optional)

For persistent history, SQL-based filtering, and richer statistics. With a remote GreptimeDB instance, the build and the AI tool don't even need to be on the same machine — see Cross-machine builds for details.

See GreptimeDB installation guide for more options.

Quick start with Docker:

docker run -d \
  --name greptime-devtap \
  --restart unless-stopped \
  -p 127.0.0.1:4000-4002:4000-4002 \
  -v ~/.devtap/greptimedb_data:/greptimedb_data \
  greptime/greptimedb:latest standalone start \
  --http-addr 0.0.0.0:4000 \
  --rpc-bind-addr 0.0.0.0:4001 \
  --mysql-addr 0.0.0.0:4002

The container runs in the background (-d) and auto-starts with Docker (--restart unless-stopped). The -v flag mounts ~/.devtap/greptimedb_data/ for persistent storage.

# Configure in ~/.devtap/config.toml (this becomes the default store)
cat > ~/.devtap/config.toml <<EOF
[store]
backend = "greptimedb"

[store.greptimedb]
endpoint = "127.0.0.1:4001"
mysql_endpoint = "127.0.0.1:4002"
database = "public"
EOF

# Now devtap uses GreptimeDB by default
devtap -- cargo check

# SQL-based filtering
devtap drain --filter-sql "content LIKE '%error%'"

# Query build error history
devtap history --since 24h

# Or override per-command (e.g., fall back to file store)
devtap --store file -- cargo check

# View logs in GreptimeDB dashboard
open http://127.0.0.1:4000/dashboard/#/dashboard/logs-query

Credentials via environment variables:

export DEVTAP_GREPTIMEDB_USERNAME=...
export DEVTAP_GREPTIMEDB_PASSWORD=...

Advanced Usage

Multiple instances — use --tag to run parallel watchers for the same session:

devtap --tag cargo-check -- cargo watch -x check
devtap --tag cargo-test --debounce 5s -- cargo watch -x test

Multi-adapter fan-out — when multiple AI tools are installed, build output is automatically delivered to all of them. Each tool independently consumes its own copy.

Cross-machine builds — with a shared GreptimeDB instance, the build and the AI tool can run on different machines. Use --session to give both sides the same logical session name:

# Machine B (your laptop) — install once, bakes --session and --store into MCP config
devtap install --adapter claude-code --session myproject --store greptimedb

# Machine A (CI / remote build server)
devtap --store greptimedb --session myproject -- make

devtap install writes the --session and --store flags into the MCP config file (e.g. .mcp.json), so the AI tool's MCP server automatically connects to the right GreptimeDB instance and session.

Multiple build machines can write to the same session simultaneously — each entry is tagged with its source, and the AI tool drains them all.

Local + remote merged drain — keep your local loop and a remote shared session visible at the same time:

# Laptop: local output (default source)
devtap -- cargo check

# Remote machine: shared session output (configured source)
devtap --store greptimedb --session myproject -- make

# Laptop: install MCP with explicit remote session
devtap install --adapter claude-code --store greptimedb --session myproject

# Optional manual check (without MCP client)
devtap drain --store greptimedb --session myproject

devtap drain shows a merged header (Draining from N sources), emits source-unreachable warnings when partial failures occur, and still returns available output from reachable sources.

Typical merged header:

[devtap] Draining from 2 sources (2 reachable)

Session auto-detection — when --session auto (default), devtap resolves the project directory like this:

1. Git root (nearest parent with .git)
2. Project marker files (nearest parent with one of: go.mod, package.json, pyproject.toml, Cargo.toml, pom.xml, build.gradle, build.gradle.kts, composer.json, Gemfile, setup.py)
3. Current working directory

Chaining commands — devtap captures a single command after --. If you need shell operators like &&, wrap the command in a shell:

devtap -- sh -c "npm install && npm run dev"

Or run them separately:

devtap -- npm install
devtap -- npm run dev

CLI Reference

devtap [flags] -- <command> [args...]

Flags:
  -a, --adapter <name>       AI tool adapter (default "claude-code")
  -s, --session <id>         Target session ("auto", "pick", or explicit name)
      --store <backend>      Storage backend ("file" or "greptimedb")
      --filter-regex <pat>   Regex filter for output lines
      --filter-invert        Invert filter (exclude matching lines)
      --max-lines <n>        Max lines per drain (default 10000)
      --tag <label>          Log tag prefix (default: command name)
      --debounce <dur>       Flush interval for captured output (default "2s", 0 to disable)

Subcommands:
  install     Configure AI tool integration (--session and --store are forwarded to MCP config)
  mcp-serve   Start MCP stdio server
  drain       Read pending messages as plain text
                -q, --quiet      Raw output without source/tag headers
  status      Show pending message counts
                -q, --quiet      Compact output (pending count only)
  history     Query build error history (GreptimeDB only)
                --since <dur>    Time range (default "24h")
                --tag <label>    Filter by tag
                --limit <n>      Max entries (default 20)
  gc          Remove expired session data (default TTL: 7 days)

Lines exceeding --max-lines are smart-truncated: head and tail preserved with omission notice. Consecutive duplicate lines are merged.

devtap mcp-serve and devtap drain can aggregate multiple sources (local + configured) as described above. devtap drain --filter-sql is a single-source mode and requires --store greptimedb.

Troubleshooting

• No output but you expect logs: run devtap status first, then devtap drain --max-lines 200.
• Using an unexpected session: run with --session pick once to confirm the target session.
• Multi-source drain shows warnings: reachable sources are still returned; warnings indicate one source is unavailable.
• MCP tool not being called: re-run devtap install --adapter <adapter> in the project root and restart the AI tool session.

Security & Privacy

• All data stays local. Build output is stored on your machine at ~/.devtap/ (file backend) or in a self-hosted GreptimeDB instance. Nothing is sent to external servers.
• MCP communication is local stdio. The MCP server runs as a child process of your AI tool, communicating via stdin/stdout JSON-RPC. No network sockets are opened.
• No telemetry. devtap collects no usage data, analytics, or crash reports.
• --filter-sql is not a security boundary. It includes a best-effort keyword blocklist but is designed for convenience, not adversarial input. The user already has full local and database access.
• Cleanup: Run devtap gc to remove expired session data, or delete ~/.devtap/ entirely to remove all stored data.

License

MIT