Borrowing it
Nothing to install: this file belongs to libtmux/libtmux-go. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/libtmux/libtmux-go/master/.agents/skills/testing-the-mcp-server/SKILL.mdgit clone --depth 1 https://github.com/libtmux/libtmux-goWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/libtmux/libtmux-go/testing-the-mcp-server)<a href="https://agentmods.dev/skills/libtmux/libtmux-go/testing-the-mcp-server"><img src="https://agentmods.dev/badge/skills/libtmux/libtmux-go/testing-the-mcp-server/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/libtmux/libtmux-go/testing-the-mcp-server"><img src="https://agentmods.dev/badge/skills/libtmux/libtmux-go/testing-the-mcp-server.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00145 | $0.01909 |
| Opus 5.5 | $0.00058 | $0.00764 |
| Sonnet 5.5 | $0.00029 | $0.00382 |
| Haiku 4.5 | $0.00015 | $0.00191 |
Grade A, and why
testing-the-mcp-server scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 11d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 192 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Testing the MCP server
go test ./... proves the handlers. It does not prove that a client can
discover a tool, get past an approval gate, call it with arguments a model
would actually send, and survive cancelling it mid-flight. Those failures live
in the gap between the in-memory transport the Go tests use and a real process
speaking JSON-RPC over a pipe.
One socket, chosen once
The Python server takes socket_name on every targeted tool, so a client picks
the tmux per call. This one does not: an operator picks the socket at launch
and a client reaches only that socket.
$ libtmux-mcp -socket-name mcp-target
LIBTMUX_SOCKET names it when no flag does, matching the Python server, so one
configuration serves both. A flag wins over the variable. Ask the server which
it took rather than assuming — -doctor names the origin:
$ libtmux-mcp -doctor
Three tmux servers, never one
| Role | Socket | Who touches it |
|---|---|---|
| The real session | default | a person, interactively — never a test |
| Harness | tmux -L cli-harness |
the driver, sending keys to a CLI's TUI |
| Target | tmux -L mcp-target |
the server under test, via -socket-name |
Keeping the target apart from the harness is the load-bearing part: a destructive tool call on the socket hosting the agent's own TUI tears down the agent mid-test, and its redraws pollute every capture.
Give the whole run its own root so a sibling checkout's suite cannot end a server this one is using:
$ export TMUX_TMPDIR=/tmp/libtmux-go-probe && mkdir -p "$TMUX_TMPDIR" && unset TMUX TMUX_PANE
Climb only as high as the question needs
Layer 0 — the real binary over raw JSON-RPC
Fastest and most deterministic, it covers process boundaries the Go tests do
not: framing, protocol negotiation, and the environment a client actually
supplies. references/drive.py is that driver:
it spawns the binary with an environment it builds rather than inherits, holds
stdin open, matches replies by id, declines any question the server asks, and
reads a plan of JSON-RPC calls from stdin.
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 11d ago Changed 4b9a0509160f
- 1mo ago Changed · +3 lines 91c6ad968600
- 2mo ago First seen · 189 lines · 145 tokens per session scan A 1a06e02ee6e3
testing-the-mcp-server is a skill published in the GitHub repository libtmux/libtmux-go (0 stars, last pushed today), licensed MIT. It adds 145 tokens to every session and 1,909 once invoked, about $0.0006 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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