Notes on SKILL.md vs MCP

Like everyone else, I’ve been looking at SKILL.md files and tried converting some of my tooling into that format. While it’s an interesting approach, I’ve found that it doesn’t quite work for me as well as does, which is… intriguing.

Concrete Example

Besides a bunch of projects, I have been using to manage this site content for a while now, and one of the things I need to do over time is to convert a bunch of legacy posts from into format. To facilitate this, I built an server (using umcp) that provides a bunch of utilities to help with the conversion:

Tool Short description
audit_file Audit a Markdown page’s reference links for missing/normalized internal targets.
audit_markdown Audit raw Markdown text for internal link correctness (not file-based).
bulk_list_dir Batch list directory entries for multiple relative paths.
check_links Check multiple internal wiki link targets and report existence.
extract_links Extract and classify inline/reference links from a page (internal/external/assets).
find_missing_internal Scan the wiki for missing internal link targets (global audit).
fix_whitespace Normalize whitespace in a wiki file (trim trailing spaces, collapse blank lines).
get_capabilities Return a capabilities snapshot and wiki statistics (counts/features).
get_lisbon_time Return current Europe/Lisbon local time formatted for frontmatter.
get_pages List all index.* page paths under the space/ directory.
get_shorthands Inspect dynamic shorthand mappings (active vs ambiguous).
help Return detailed schema & usage examples for a named tool.
html_to_markdown Convert HTML snippets to Markdown using markitdown (requires deps).
list_legacy_index_txt List legacy index.txt files that don’t have a corresponding index.md.
optimize_image Optimize one or more image files using platform-specific tools (ImageOptim/Curtail).
refresh_shorthands Rebuild the shorthand mapping from current wiki pages.
resolve_internal Suggest canonical page paths for outdated or shorthand internal targets.
restart_server Exit the MCP server cleanly so it can be restarted (use after code changes).
search_internal_usage Find pages referencing a particular internal target.
textile_to_markdown Convert Textile snippets to Markdown via HTML → markitdown (requires deps).
validate_yaml Validate YAML files using PyYAML and a whitelist of value types.


Yeah, I might have gone a bit overboard with the number of tools, but it turns out reliably converting thousands of ancient pages has a lot of corner cases…

MCP Workflow Chaining

Now, I of , but What I’ve found is that allows me to implicitly chain tool invocations, whereas the SKILL.md approach seems to require very explicit step-by-step instructions and it’s almost completely impossible to “chain” skills together in a meaningful way.

For example, one of the most useful things I can do when converting a page is to audit its internal links, extract all the references, resolve any ambiguous or missing targets, and then update the page with normalized links. In my server, I can return the next steps for a workflow as part of the prompts associated with each tool, like so:

# excerpt from prompt_explain_tool (simplified)
if "audit_file" in name:
    workflow = [
        "call tool_audit_file(path=...) to get missing/present link sets",
        "resolve ambiguous/missing via tool_resolve_internal / tool_find_missing_internal",
        "(optional) update links using planning prompt",
        "re-run tool_audit_file to confirm clean state",
    ]
elif "extract_links" in name:
    workflow = [
        "(optional) run tool_audit_file(detail=true) first",
        "invoke tool_extract_links to enumerate link references",
        "plan link normalizations (prompt_update_markdown_links)",
        "apply edits & re-audit",
    ]

# Related tools are chosen from candidates that co-occur in workflows
related_candidates = [
    "tool_audit_file",
    "tool_extract_links",
    "tool_resolve_internal",
    "tool_find_missing_internal",
    "tool_get_pages",
    "tool_refresh_shorthands",
    "tool_bulk_list_dir",
]
related_tools = [t for t in related_candidates if t in " ".join(workflow) or t.startswith(f"tool_{verb}")]

# Recommend a next tool based on the workflow focus
if "audit_file" in name:
    recommended_next = ["tool_resolve_internal"]
elif "extract_links" in name:
    recommended_next = ["tool_update_markdown_links"] if "tool_update_markdown_links" in registry else ["tool_audit_file"]
else:
    recommended_next = related_tools[:1]

# this is what gets returned to the model
scaffold = {
    "tool": name,
    "summary": meta.get("description", ""),
    "workflow": workflow,
    "related_tools": related_tools,
    "recommended_next": recommended_next,
}

People who’ve used promptflow or similar frameworks will recognize this pattern of “next steps” prompting, and it works quite well in practice. The model can see the context of what it’s doing, what comes next, and how the tools relate to each other, so it can chain invocations naturally.

Where SKILL.md Falls Short

With SKILL.md, however, no matter how many “next steps”, “related skills”, or “CRITICAL: MUST DO IN THIS ORDER” admonitions I add, even frontier models like Claude Opus 4.5 or gpt-5 struggle to chain the steps together. Each skill invocation tends to feel isolated, and I frequently have to intervene to connect the dots.

My convert-legacy skill is huge (around twice the size of this post so far) and contains dozens of explicit steps and quality requirements, but models still miss crucial transitions or misinterpret the intended flow, so it feels like I’m constantly fighting the format rather than using it.

But, more to the point, simpler skills don’t fare better. A skill to audit a file’s links and suggest fixes should be straightforward, but I’ve seen models completely ignore the “suggest fixes” part or fail to produce actionable output unless I break it down into even more granular skills, which not only also doesn’t work but further defeats the purpose of having a higher-level abstraction in the first place.

By contrast, with my server, even when using smaller models like haiku or gpt-5-mini, the implicit workflows are more reliable because the tools narrow the context and present the models with next steps.

This example is one I can share publicly, but over the past few months I’ve seen this pattern time and again across many implementations and use cases.

We sometimes “fix” the problem by upgrading to a higher-tier model, but that incurs cost and latency (Claude Opus 4.5, for example, is neither cheap nor fast). So at least for now, even considering , I prefer the more deterministic behavior of for complex multi-step tasks, and the fact that I can do it effectively using smaller, cheaper models is just icing on the cake.

When OpenCode decides to use a Chinese proxy

So here’s my cautionary tale for 2026: I’ve been testing toadbox, my very simple, quite basic coding agent sandbox, with various .

I’m running the agent containers inside , and I decided to tweak the VLAN configuration I was using for the VM running the containers, with the result that it temporarily lost DNS access (so, effectively, “internet access”, except for connections that were already established).

When I connected back to one of the containers, I noticed that OpenCode (which I’m running inside toad, since I very much prefer its text UI) had decided to route the package installations through a Chinese proxy server:

Now that was a surprise...
Now that was a surprise...

I terminated the container immediately, and checked the workspace files (nothing untoward there that I could see, except for a couple more test files in the target project), but it was a stark reminder that LLMs are not to be trusted blindly.

Just for clarification, I was using OpenCode’s out-of-the-box default settings, with no custom configuration. toadbox just installs toad, which then installs OpenCode off its startup menu, and I did no setup whatsoever. So I was using one of their default free models.

Digging around in a fresh container the default model I’m getting is big-pickle, and I have to assume that this is the one that decided to use that proxy–and going forward, now that I know where OpenCode is saving its log files, I’ll be adding a docker volume to toadbox to capture those logs outside the container for future reference.

Like I posted on Hacker News, this is interesting for several reasons–the first is that even with tool whitelisting this kind of thing might happen, and the second is the why. I happen to know about how popular Go is in China and that the proxy approach is… well… kinda official, but it’s also a great demonstration of how leverage “knowledge” in a completely non-linear way.

Considering that one of Simon Willison’s predictions for 2026 was that we are finally going to solve sandboxing for LLMs this year, I guess this is a timely reminder that we still have a long way to go.

But his other prediction about there being a “Challenger disaster” for coding agent security feels a lot closer to reality now…

Update: I did some spelunking since the container was actually still around (I just killed it, didn’t remove it) and confirmed that this was indeed big-pickle. Here’s the relevant excerpt from the logs showing the agent seting the Go proxy (“fortunately” it goes through google.cn, but… you get the idea):

INFO  2026-01-12T17:27:08 +0ms service=acp-agent event={"part":{"id":"prt_bb33f4a91001cjhLK5GlGb6JtS","sessionID":"ses_452fc8c2affeug9efc7DE65VRd","messageID":"msg_bb33f37d3001j20t9IKK6MN569","type":"tool","callID":"call_1ed63d94eb3140709de6c67c","tool":"bash","state":{"status":"running","input":{"command":"cd /home/me/Sync/Development/Experimental/gotel && go env -w GOPROXY=https://goproxy.cn,direct","description":"Try Chinese Go proxy"},"time":{"start":1768238828180}}}} message part updated
INFO  2026-01-12T17:27:08 +1ms service=server method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +0ms service=server status=started method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +0ms service=server status=completed duration=0 method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +0ms service=acp-agent event={"part":{"id":"prt_bb33f4a91001cjhLK5GlGb6JtS","sessionID":"ses_452fc8c2affeug9efc7DE65VRd","messageID":"msg_bb33f37d3001j20t9IKK6MN569","type":"tool","callID":"call_1ed63d94eb3140709de6c67c","tool":"bash","state":{"status":"running","input":{"command":"cd /home/me/Sync/Development/Experimental/gotel && go env -w GOPROXY=https://goproxy.cn,direct","description":"Try Chinese Go proxy"},"metadata":{"output":"","description":"Try Chinese Go proxy"},"time":{"start":1768238828182}}}} message part updated
INFO  2026-01-12T17:27:08 +0ms service=server method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +0ms service=server status=started method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +1ms service=bus type=message.part.updated publishing
INFO  2026-01-12T17:27:08 +1ms service=server status=completed duration=2 method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +0ms service=acp-agent event={"part":{"id":"prt_bb33f4a91001cjhLK5GlGb6JtS","sessionID":"ses_452fc8c2affeug9efc7DE65VRd","messageID":"msg_bb33f37d3001j20t9IKK6MN569","type":"tool","callID":"call_1ed63d94eb3140709de6c67c","tool":"bash","state":{"status":"completed","input":{"command":"cd /home/me/Sync/Development/Experimental/gotel && go env -w GOPROXY=https://goproxy.cn,direct","description":"Try Chinese Go proxy"},"output":"","title":"Try Chinese Go proxy","metadata":{"output":"","exit":0,"description":"Try Chinese Go proxy"},"time":{"start":1768238828180,"end":1768238828185}}}} message part updated
INFO  2026-01-12T17:27:08 +0ms service=server method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +0ms service=server status=started method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request
INFO  2026-01-12T17:27:08 +1ms service=server status=completed duration=1 method=GET path=/session/ses_452fc8c2affeug9efc7DE65VRd/message/msg_bb33f37d3001j20t9IKK6MN569 request

Oh, and I was just sent this RCE report for OpenCode too, so… yeah. Be careful out there.

Lisbon Film Orchestra

Great start to the show
A little while ago, in a concert hall not that far away…

How I Manage My Personal Infrastructure in 2026

As regular readers would know, I’ve been on the homelab bandwagon for a while now. The motivation for that was manifold, starting with the pandemic and a need to have a bit more stuff literally under my thumb.

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Notes for December 25-31

OK, this was an intense few days, for sure. I ended up going down around a dozen different rabbit holes and staying up until 3AM doing all sorts of debatably fun things, but here’s the most notable successes and failures.

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TIL: Restarting systemd services on sustained CPU abuse

I kept finding avahi-daemon pegging the CPU in some of my LXC containers, and I wanted a service policy that behaves like a human would: limit it to 10%, restart immediately if pegged, and restart if it won’t calm down above 5%.

Well, turns out systemd already gives us 90% of this, but the documentation for that is squirrely, and after poking around a bit I found that the remaining 10% is just a tiny watchdog script and a timer.

Setup

First, contain the daemon with CPUQuota:

sudo systemctl edit avahi-daemon
[Service]
CPUAccounting=yes
CPUQuota=10%
Restart=on-failure
RestartSec=10s
KillSignal=SIGTERM
TimeoutStopSec=30s

Then create a generic watchdog script at /usr/local/sbin/cpu-watch.sh:

#!/bin/bash
set -euo pipefail

UNIT="$1"
INTERVAL=30

# Policy thresholds
PEGGED_NS=$((INTERVAL * 1000000000 * 9 / 10))   # ~90% of quota window
SUSTAINED_NS=$((INTERVAL * 1000000000 * 5 / 100)) # 5% CPU

STATE="/run/cpu-watch-${UNIT}.state"

current=$(systemctl show "$UNIT" -p CPUUsageNSec --value)
previous=0
[[ -f "$STATE" ]] && previous=$(cat "$STATE")
echo "$current" > "$STATE"

delta=$((current - previous))

# Restart if pegged (hitting CPUQuota)
if (( delta >= PEGGED_NS )); then
  logger -t cpu-watch "CPU pegged for $UNIT (${delta}ns), restarting"
  systemctl restart "$UNIT"
  exit 0
fi

# Restart if consistently above 5%
if (( delta >= SUSTAINED_NS )); then
  logger -t cpu-watch "Sustained CPU abuse for $UNIT (${delta}ns), restarting"
  systemctl restart "$UNIT"
fi

…and mark it executable: sudo chmod +x /usr/local/sbin/cpu-watch.sh

It’s not ideal to have hard-coded thresholds or to hit storage frequently, but in most modern systems /run is a tmpfs or similar, so for a simple watchdog this is acceptable.

The next step is to make it executable and figure out how to use it via systemd templates:

sudo chmod +x /usr/local/sbin/cpu-watch.sh
# cat /etc/systemd/system/[email protected]
[Unit]
Description=CPU watchdog for %i
After=%i.service

[Service]
Type=oneshot
ExecStart=/usr/local/sbin/cpu-watch.sh %i.service
# cat /etc/systemd/system/[email protected]
[Unit]
Description=Periodic CPU watchdog for %i

[Timer]
OnBootSec=2min
OnUnitActiveSec=30s
AccuracySec=5s

[Install]
WantedBy=timers.target

The trick I learned today was how to enable it with the target service name:

sudo systemctl daemon-reload
sudo systemctl enable --now [email protected]

You can check it’s working with:

sudo systemctl list-timers | grep cpu-watch
# this should show the script restart messages, if any:
sudo journalctl -t cpu-watch -f

Why This Works

The magic, according to Internet lore and a bit of LLM spelunking, is in using CPUUsageNSec deltas over a timer interval, which has a few nice properties:

  • Short CPU spikes are ignored, since the timer provides natural hysteresis
  • Sustained abuse (>5%) triggers restart
  • Pegged at quota (90% of 10%) triggers immediate restart
  • Runaway loops are contained by CPUQuota
  • Everything is systemd-native and auditable via journalctl

It’s not perfect, but at least I got a reusable pattern/template out of this experiment, and I can adapt this to other services as needed.

Ovo

Yeah, I don’t know what the grasshoppers want with the egg either
Another great evening spent in the company of Cirque du Soleil

Predictions for 2026

I had a go at doing predictions for 2025. This year I’m going to take another crack at it—but a bit earlier, to get the holiday break started and move on to actually relaxing and building fun stuff.

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Notes for December 9-24

Work slowed down enough that I was able to unwind a bit more and approach the holiday season with some anticipation–which, for me, invariably means queueing up personal projects. So most of what happened in my free time over the past couple of weeks was coding-related.

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The Big Blue Room

A lovely mirror
This part of town never disappoints, even in winter.
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