# Show HN: Mcptoon – Token-efficient MCP CLI client > Source: > Published: 2026-08-11 05:26:58+00:00 **MCP tool discovery costs 10,000+ tokens. mcptoon costs 350.** *One MCP client for every AI agent. Cross-platform. Zero dependencies. Battle-tested with 255+ tools.* **If this saves you tokens, please star the repo — it helps others discover it.** [English](/activeing123/mcptoon/blob/main/README.md) | [中文文档](/activeing123/mcptoon/blob/main/README.zh-CN.md) | [Report Bug](https://github.com/activeing123/mcptoon/issues) | [Request Feature](https://github.com/activeing123/mcptoon/issues) ** What's new in v0.2.0** — stdin support, doctor command, tool poisoning guard, fuzzy match, cross-agent format export Every MCP-enabled conversation burns tokens on **syntax, not data**: - Your agent connects to 5 MCP servers. Listing their tools: **~10,000 tokens** of JSON. - Your agent calls 20 tools. Each returns 500-3,000 tokens wrapped in `{"content":[{"type":"text","text":"..."}]}` . - Total MCP overhead: **40,000-70,000 tokens** before any actual thinking happens. On a 128K context window, that's **30-55% gone**. Not on work. On syntax. mcptoon is a CLI client that connects to any MCP server (stdio or HTTP) and outputs **TOON** (Token-Optimized Object Notation) instead of JSON. | Operation | JSON tokens | mcptoon tokens | Savings | |---|---|---|---| | Tool discovery (96 tools) | ~2,000 | ~60 | 97% | | Tool result (structured data) | ~800 | ~350 | 56% | | Tool result (raw HTML/text) | ~1,000 | ~900 | 10% | Zero dependencies. Pure Python. 50KB. Works with **every AI agent** — Claude Code, Codex, OpenCode, Cursor, CatPaw, anything that runs shell commands. **JSON (287 tokens)** — what every other MCP client returns: ``` [ {"name": "search_web", "description": "Search the web for information", "inputSchema": {"type": "object", "properties": {"query": {"type": "string", "description": "Search query"}, "num_results": {"type": "number", "default": 5}}, "required": ["query"]}}, {"name": "fetch_url", "description": "Fetch content from a URL", "inputSchema": {"type": "object", "properties": {"url": {"type": "string"}}, "required": ["url"]}} ] ``` **TOON (5 tokens)** — what mcptoon returns: ``` search_web fetch_url ``` 98% reduction for tool discovery, 60% for full schema, zero information lost. ``` pip install mcptoon ``` Zero dependencies. 50KB. Python 3.10+. Windows, macOS, Linux. ``` mcptoon init # Sample config: ~/.mcptoon/config.json mcptoon add fetch --stdio npx -y @modelcontextprotocol/server-fetch mcptoon manifest --toon # -> fetch:fetch mcptoon call fetch fetch '{"url":"https://example.com"}' --toon mcptoon call fetch fetch '{"url":"https://example.com"}' --json # when you need JSON ``` | JSON | TOON | Why | |---|---|---| `{"name":"search","count":3}` | `name:search|count:3` | Pipes replace braces + quotes + colon | `[1, 2, 3]` | `1 2 3` | Spaces replace brackets + commas | `true` / `false` | `T` / `F` | 1 char vs 4-5 | `null` | `∅` | 1 symbol vs 4 chars | `"line1\nline2"` | `line1↲line2` | ↲ replaces escape sequence | `{"a":{"b":[1,2]}}` | `a:b:1_2` | Recursive compaction | | Flag | What you get | Token footprint | |---|---|---| `--toon` | Compact notation, full semantics | 40-60% less than JSON | `--compact` | Tool names only, space-separated | 97% less than JSON | `--json` | Standard JSON (for scripts, CI) | Baseline | `--raw` | Raw response, no parsing | Full size | `--head N` | First N items only | Variable | `--max-chars N` | Hard truncate at N chars | Variable | `--full` | Disable the default 4000-char truncation | Full size | Set `MCPTOON_AGENT_TYPE=claude` and every call auto-selects `--toon` . Battle-tested features from production use with 255+ MCP tools across 23+ servers: OS command-line limits (32,767 chars on Windows, ~128KB on Linux) break MCP calls with large content. Now you can pipe arguments via stdin: ``` # This fails on Windows if content > 32KB: mcptoon call fetch put '{"content":"...huge..."}' # This always works: echo '{"content":"...huge..."}' | mcptoon call fetch put --stdin --toon mcptoon call fetch put --stdin --toon < payload.json bash $ mcptoon doctor ✓ Python 3.12.0 (>=3.10 required) ✓ Config: ~/.mcptoon/config.json (5 servers) ✓ Cache dir: ~/.cache/mcptoon ✓ fetch [stdio] 1 tools ✓ github [stdio] 12 tools ✗ myapi [http] ERROR: Connection refused - MCPTOON_AGENT_TYPE not set (defaulting to auto) 5 checks, 1 issue(s) bash $ mcptoon discover Discovered 3 server(s): ✓ fetch [stdio] 1 tools ok ✓ github [stdio] 12 tools ok ✗ myapi [http] 0 tools error └─ Connection refused ``` MCP servers return arbitrary content. A compromised server could inject instructions into your agent's context. mcptoon now detects and blocks common prompt injection patterns: ``` bash $ mcptoon call malicious get_data '{}' Error [TOOL_POISONING]: Tool result may contain prompt injection: potential prompt injection detected: contains 'ignore previous instructions' ``` Patterns detected: instruction overrides, hidden `