mcptoon

Those numbers are ours, but "loading every tool schema into context is expensive" is not a claim only we make:

• Anthropic: tool schemas flooding the context window is a real pain — one example drops from 150,000 tokens to 2,000 (a 98.7% saving)
• Firecrawl benchmark: the same task cost 1,365 tokens via CLI vs 44,026 via MCP — 32× (full schema loaded upfront)
• Scalekit benchmark: CLI is 10–32× cheaper and 100% reliable; MCP scores 72%
• MCP-Zero (arXiv:2506.01056): on-demand tool retrieval achieves near-constant cost regardless of tool count
• SEP-1576: an open MCP proposal to cut schema redundancy — the problem is acknowledged upstream

We're not the only ones who measured this. mcptoon is the one you can use today, covering every agent at once.

pip install mcptoon                          # pure stdlib, 128KB, zero dependencies

# Add any MCP server — one command:
mcptoon add fetch --stdio npx -y @modelcontextprotocol/server-fetch

# See every tool available (names-only by default; 255 tools cost 581 tokens):
mcptoon manifest

# Call a tool (JSON output by default; add --toon to save more):
mcptoon call fetch fetch '{"url":"https://example.com"}'

Or let mcptoon auto-discover servers already on your machine:

mcptoon quickstart     # discover + configure + list tools — one command

That's it. No hand-written JSON config. No MCP protocol debugging. No polluted context window.

Every MCP agent (Claude Code, Cursor, Codex, …) stuffs every tool's full schema into your context window before doing any work:

50 tools  → 14,113 tokens of schema → a 128K context: 11% gone
255 tools → 71,929 tokens of schema → a 128K context: 56% gone

So you unload servers you aren't using and reload them when you are. Back and forth. Adding one new server still means hand-writing a JSON config — one missing comma and everything breaks.

mcptoon fixes this. Your MCP servers stay configured, but their schemas never enter the agent's context by default. The agent just runs mcptoon commands, and only the compact result you asked for enters context — the name index weighs 581 tokens (114 for 50 tools, −99.2%).

Without mcptoon: 255 tools → 71,929 tokens, over half the window
With mcptoon:    255 tools → 581 tokens. 99.2% saved.

Both rows are measured configurations, not one number scaled up and down (tiktoken cl100k_base, assets/benchmark_tiktoken.json). Your mix will differ — compute your own numbers in the browser, 30 seconds, nothing uploaded.

# Install from npm (most MCP servers live here):
mcptoon install brave-search --npm @modelcontextprotocol/server-brave-search

# Install from pip:
mcptoon install my-tool --pip mcp-my-tool

# HTTP/SSE servers:
mcptoon install remote-api --url https://example.com/mcp

# List installed:
mcptoon install --list

# Uninstall:
mcptoon install --remove brave-search

mcptoon connects, discovers tools, generates the handler, registers it. No restart needed.

Any MCP server works:

mcptoon add my-server --stdio npx -y @any/mcp-package
mcptoon manifest    # usable immediately

Don't want to hand-edit configs? ToonDeck is a local console for mcptoon: every MCP server and tool in one place with a real health check, one skill folder synced to all your agents, agent launching with live logs, and API keys stored in your OS keychain — never in a plaintext file.

pip install toondeck    # ships the web UI inside the wheel — no node, no build

Pre-alpha; free (Apache-2.0). ToonDeck drives the engine — mcptoon stays the single source of truth underneath.

mcptoon is a CLI. If your agent can run a shell command, it can use mcptoon. No plugins, no SDK, no per-agent setup.

Configure once in ~/.mcptoon/config.json; every agent that can run shell commands shares the same servers and tools. GUI agents that can't? mcptoon sync writes native JSON into each one's own location.

export MCPTOON_AGENT_TYPE=claude   # call results auto-select --toon
# export MCPTOON_AGENT_TYPE=openai   # or keep the default JSON

Your AI can even add tools by itself — no human in the loop:

# Agent needs GitHub access mid-task? It just runs:
mcptoon add github --stdio npx -y @modelcontextprotocol/server-github
mcptoon call github search_repos '{"query":"mcp"}'
# Done. No JSON editing. No restart. No lost context.

mcptoon's token savings are two separate bills — know which one you're reading before comparing numbers.

This bill comes due before your agent decides "which tool do I use". Native MCP shoves every tool's full schema into context (50 tools: 14,113 tokens; 255 tools: 71,929 tokens). mcptoon sends only the name index — that's where "114, not 14,113" comes from.

Zero action, on by default: mcptoon manifest with no flags is this tier. Want to give the agent more? --full (names + parameter types) saves 88.5%; --json (full schema) is the baseline.

Both rows are measured configurations, not one number scaled up and down (tiktoken cl100k_base, assets/benchmark_tiktoken.json). Your mix will differ — compute your own numbers in the browser, 30 seconds, nothing uploaded.

This bill comes due after a tool returns its result to your agent. mcptoon call outputs JSON by default — yes, the default saves nothing. To shrink results too, add --toon (structured encoding, reversible):

Default:  mcptoon call fetch fetch '{"url":"https://example.com"}'   → JSON (baseline)
Leaner:   mcptoon call fetch fetch '{"url":"https://example.com"}' --toon   → ~34% saved

34% is the measured toon_save value in assets/benchmark_tiktoken.json (34.0–34.2%), not a marketing number.

One line to remember: 99.2% is what you save seeing which tools exist; 34% is what you can further save on results.

Without mcptoon (what every MCP client stuffs into context — 37 tokens, measured with tiktoken):

[{"name":"search_web","description":"Search the web for information",
"inputSchema":{"type":"object","properties":{"query":{"type":"string","description":"Search query"}}}}]

With mcptoon (2 tokens):

search_web

With mcptoon --full (6 tokens, parameter info included):

search_web|query:s*

Three layers, all built in:

• No telemetry. No analytics, no crash reports, no call-home.
• No stored credentials. API keys pass straight from your config or environment.
• No dependencies. Pure Python standard library. Nothing in the supply chain to audit.
• No daemon. Pure CLI — no resident process, no listening port, no attack surface.

mcptoon quickstart              # one-shot start (discover + configure + list tools)
mcptoon list                    # show configured servers
mcptoon manifest                # all tool names (compact by default; 255 tools = 581 tokens)
mcptoon manifest --full         # tool schemas with params (88.5% smaller than native)
mcptoon inspect <server> <tool> # inspect one tool's schema
mcptoon search <query>          # search tools across servers
mcptoon call <server> <tool> '{"args":"here"}'   # call a tool
mcptoon call --auto <tool> '{"args":"here"}'     # auto-find the server
mcptoon call <server> <tool> --stdin             # read large args from stdin
mcptoon add <name> --stdio|--http <cmd|url>     # add any MCP server
mcptoon remove <name>           # remove a server
mcptoon install <name> --npm|--pip|--url <pkg>  # install + auto-generate handler
mcptoon install --list          # list installed
mcptoon install --remove <name> # uninstall
mcptoon sync                    # sync native config to every detected agent
mcptoon plugin install <dir>    # install an Agent Plugins 1.0.0 plugin
mcptoon serve                   # run as an MCP server (stdio/HTTP)
mcptoon demo                    # one command, live demo on your machine
mcptoon doctor                  # self-check: Python, config, connectivity
mcptoon usage                   # local call statistics
mcptoon completion ps           # shell completion (bash/zsh/fish/powershell)

Discovery and call results each have a set of formats — all optional, and the default is already the leanest tier:

manifest (discovery): compact by default, upgrade only if you want more

Why compact by default, not full? Deciding "which tool do I use" only needs names (581 tokens for 255 tools); parameter details matter at call time, fetched on demand via inspect or manifest --full. Defaulting to full schemas hands the 99.2% right back.

call (results): JSON by default, --toon to save

Where these formats come from

• compact: a name list — any tool manager can do it; nothing proprietary.
• slim (name|param:type* signatures): an mcptoon original, implemented in output.py (slim_toon, Apache 2.0); noted in NOTICE.
• full: full JSON Schema — what MCP speaks natively.
• toon (result encoding): integration of the open TOON standard (toon-format/toon v4.1, MIT), vendored from python-toon and credited in NOTICE — not our invention, and we don't claim it.

"Proprietary format = compatibility bomb" is a fair worry. It doesn't apply here:

1 · The protocol layer is always standard JSON-RPC; formats live only in the presentation layer. mcptoon speaks standard MCP to servers (initialize / tools/list / tools/call). compact/slim/toon only affect the "mcptoon → agent" output rendering — not a single byte toward the server. Servers always see standard JSON; they don't even know these formats exist.

2 · --toon isn't proprietary; it's an open standard. TOON (Token-Oriented Object Notation) is an external open standard (toon-format/toon v4.1, MIT, official TypeScript reference implementation). We integrate python-toon (MIT); tests/test_toon_cross_validate.py verifies decode(encode(x)) == x case by case.

3 · There's a fallback; worst case you fall back to JSON. If --toon decoding fails it falls back to JSON automatically (--fallback-json); and call results are JSON by default anyway — --toon is optional. Want the full schema back? One --full is native MCP. No lock-in.

In one line: zero protocol changes, formats live in the output layer, worst case falls back to JSON. The feared "server can't understand the custom format" can't happen — servers always hear standard JSON-RPC.

mcptoon is a CLI tool, not an MCP client library. Your agent doesn't connect to MCP servers — it runs mcptoon commands. Schemas live on disk in ~/.mcptoon/config.json, out of the context window by default.

Two-layer decoupling:

Layer 1: mcptoon CLI (128KB, zero deps)
         runs in the agent's shell. schemas stay out of context by default.
                    │
Layer 2: the actual MCP servers (npm/pip packages)
         start only when a tool is called. Zero cost when idle.

• 1,000 servers configured → 0 running, until you call one
• mcptoon bundles nothing — you add what you want, one command each
• Delete mcptoon? Your MCP servers keep running independently

MCP's premise: every capability is a server, and your agent must be configured to reach it. That premise is why one new tool means editing per-agent JSON in a different format for each, restarting everything — and why every agent re-pays the full schema cost before doing anything.

A command line is the one interface every agent already has. And the form factor is measurably cheaper, independent of anything mcptoon does:

• Firecrawl's benchmark: the same task cost 1,365 tokens via CLI vs 44,026 via MCP — 32×
• Scalekit's benchmark: CLI 10–32× cheaper, 100% reliable vs MCP's 72%

If you truly need the proxy form, mcptoon serve is that mode — all configured servers behind one MCP endpoint, with connection pooling and per-agent API keys.

git clone https://github.com/activeing123/mcptoon.git
cd mcptoon
pip install -e . --no-build-isolation
pip install pytest pytest-cov
python -m pytest tests/ -v   # 738 passed, 1 skipped

Zero dependencies is a hard rule. New features need tests. See CONTRIBUTING.md and DEVELOPERS.md.

The codebase: 11,400 lines of Python across 21 modules, zero third-party dependencies.