DuckTap

Turn any OpenAPI spec into a working MCP server in one command — deterministically.

No LLM. No API key. No Claude Code. ducktap press ./openapi.yaml reads the spec and prints an MCP server — plus a Python CLI and an agent skill — that any agent can use. Same spec → same output, every time. Runs in CI.

Website: ducktap-website.vercel.app

$ ducktap press ./openapi.yaml --name petstore
Pressed petstore (19 operations) -> out
  python-cli: 11 files
  mcp-server: 5 files
  skill:      3 files

Scorecard: 87/100 (B)
  - coverage:      95  -- 19 operations exposed
  - documentation: 100 -- 19/19 operations have docs
  - auth:          100 -- 2 auth scheme(s)
  - typed_params:  54  -- 29/53 params typed/enum
  - artifacts:     100 -- 3/3 expected artifact dirs present
  - naming:        100 -- 19/19 unique operation ids

Why deterministic? DuckTap parses the spec and emits code directly — no model in the loop. That means no API key, no per-run token cost, reproducible output you can diff and review, and generation that runs in CI.

Inspired by Printing Press by @mvanhorn — same north star (muscle memory for agents). Printing Press is the prompt-driven, Claude-Code-native take; DuckTap is the spec-first, deterministic one. Here's an honest DuckTap vs Printing Press on when to use which.

Why a CLI factory?

In a world of AI agents, a well-designed CLI is muscle memory. No hunting through docs, no wrong turns, no wasted tokens. DuckTap reads the spec, sniffs the traffic when no spec exists, and prints:

• A Python CLI (<api>-dt-cli) -- Click-based, auth from env vars, JSON by default, pretty mode for humans, local SQLite mirror with FTS5 full-text search, compound query commands (stale, health, bottleneck), retries on transient errors.
• TypeScript CLI (<api>-dt-ts) -- oclif-based for Node.js teams.
• Go CLI (<api>-dt-go) -- cobra-based, single binary.
• Rust CLI (<api>-dt-rs) -- clap-based, single binary distribution.
• An MCP server (<api>-dt-mcp) -- every operation exposed as an MCP tool, stdio transport, drop into Claude Desktop or Cursor in 60 seconds.
• A skill for Claude Code, Cursor (.mdc), and a generic tools.json -- so any agent harness can pick up where the others left off.
• A scorecard grading coverage, docs, auth clarity, typed params, artifacts, and naming.

Install

pip install ducktap
ducktap --version

For browser sniffing (optional):

pip install "ducktap[sniff]"
playwright install chromium

Requires Python 3.11+.

Developer install (contributing to DuckTap itself)

git clone https://github.com/zanni098/DuckTap
cd DuckTap
pip install -e ".[dev]"
python -m pytest tests/ -q   # 85+ passed

Quick start

# 1. Press a built-in catalog entry (no URL needed)
ducktap catalog list                  # browse 30+ built-in APIs
ducktap catalog print stripe          # press Stripe CLI + MCP + skill

# 2. From any OpenAPI spec URL
ducktap press https://petstore3.swagger.io/api/v3/openapi.yaml

# 3. From a local spec or HAR file
ducktap press ./openapi.yaml --name myapi
ducktap press ./traffic.har  --name myapi

# 4. From a website with no public spec (needs [sniff] extra)
ducktap sniff https://example.com

# 5. Open the dashboard
ducktap ui    # http://127.0.0.1:8765

Running ducktap press prints something like:

Pressed petstore (19 operations) -> ./out
  python-cli: 10 files
  mcp-server:  5 files
  skill:       3 files

Scorecard: 92/100 (A)
  - coverage:      95  -- 19 operations exposed
  - documentation: 100 -- 19/19 operations have docs
  - auth:          100 -- 2 auth scheme(s)
  - typed_params:   54 -- 29/53 params typed/enum
  - artifacts:     100 -- 3/3 expected artifact dirs present
  - naming:        100 -- 19/19 unique operation ids

What you get under ./out/:

out/
├── petstore-dt-cli/        # pip install -e .  →  petstore-dt-cli --help
│   ├── pyproject.toml
│   ├── README.md
│   ├── petstore_dt_cli/
│   │   ├── main.py
│   │   ├── commands.py     # one click subcommand per API operation
│   │   ├── client.py       # httpx + env-var auth + retries
│   │   └── mirror.py       # local SQLite cache
│   └── tests/test_smoke.py
├── petstore-dt-mcp/        # pip install -e .  →  add to Claude Desktop config
│   └── petstore_dt_mcp/server.py
└── skills/ducktap-petstore/
    ├── SKILL.md            # Claude Code skill
    ├── ducktap-petstore.mdc  # Cursor rule
    └── tools.json          # generic agent tool definitions

How DuckTap improves on Printing Press

	Printing Press	DuckTap
Language	Go	Python -- easier to extend, richer LLM ecosystem
LLM	Claude only	Multi-LLM via LiteLLM (Anthropic, OpenAI, Gemini, Ollama, Groq, Azure)
Skills	Claude Code	Claude Code + Cursor .mdc + generic tools.json
UI	None	Local FastAPI dashboard (ducktap ui)
Plugins	Source fork	Entry-point plugin system -- drop-in discoverers & generators
Browser sniff	Custom Go browser	Playwright -- full HAR export, scriptable actions
Generated CLI runtime	Single Go binary	Python (pip-installable, hackable, single-file editable)

See docs/COMPARISON.md for the full feature matrix.

Commands

ducktap press <source>          # discover + generate (the default loop)
ducktap research <source>       # discover only -- emit normalized APISpec JSON
ducktap sniff <url>             # browser-sniff a site (needs [sniff] extra)
ducktap scorecard <source>      # quality scorecard
ducktap shipcheck <name>        # structural & runtime sanity checks
ducktap catalog list|print      # browse the recipe library
ducktap plugins list            # show installed discoverers + generators
ducktap ui                      # local web dashboard

Plugins

Add a discoverer or generator without forking. Register via Python entry points:

# your_plugin/pyproject.toml
[project.entry-points."ducktap.plugins"]
mything = "your_plugin.module"   # module just calls plugins.register_discoverer(...)

See docs/PLUGINS.md and the sample at src/ducktap/plugins/builtin/graphql_intro.py.

Architecture

input (URL | spec | HAR)
        │
        ▼
  ┌─────────────┐
  │  Discovery  │   openapi / har / browser-sniff / graphql (plugin) / ...
  └──────┬──────┘
         ▼
   APISpec (Pydantic) ──── intermediate normalized representation
         │
         ▼
  ┌─────────────┐
  │  Generator  │   python-cli / mcp-server / skill / ...
  └──────┬──────┘
         ▼
  artifacts/       (CLI pkg + MCP pkg + SKILL.md + cursor.mdc + tools.json)
         │
         ▼
  ┌─────────────┐
  │   Verify    │   scorecard + shipcheck + (optional) live smoke test
  └─────────────┘

See docs/ARCHITECTURE.md.

Roadmap

See docs/ROADMAP.md. Highlights for v0.4+:

• Compound command macros -- YAML recipes that chain API calls with step references
• FTS5 full-text search over saved JSON responses in the local data lake
• DuckDB backend as an alternative to SQLite for analytical workloads
• Top-level query command for SQL over the mirror
• CLI publish to PyPI + GitHub in one command

License

MIT -- see LICENSE.

Acknowledgements

Inspired by Printing Press by Matt Van Horn and the agent-CLI playbook proved out by discrawl and gogcli.