I tested DeepSeek Harness for a week. I left with a shipped plugin and $0 in API costs

I came to DeepSeek Harness as a reviewer and left as one of its plugin authors,
which is a fair measure of how the week went.

The hook is on the repo's first line: "Everything is a plugin." Not the
usual marketing meaning — not a config file with a couple of third-party hooks.
In DSH the agent hosts its own web UI as plugin packages; the settings screen
where you pick and configure models is assembled from plugin contributions
(this is the part I verified the hard way); even the optional subagents —
Codex, Claude Code — ship as plugins you can add or drop. All of it loaded
through manifests over a real extension API. I've poked at a lot of "extensible" tools. This one takes it literally, and poking at it turned into
the most fun I've had with an agent harness in a while.

The test project: a pricing board inside the harness itself

The gap I kept feeling in Settings → Models was the two questions I ask before
switching providers every time: what does this model actually cost per
million tokens, and is a cheaper route to the same model available? DSH
tells you which models exist. It doesn't tell you what they cost.

dsh-model-pricing closes that, and it lives inside the harness's own
Settings page — because that's the point of testing the plugin system:

• per-1M-token input / output / cache prices for 7,178 priced models across 213 providers (models.dev data)
• the harness's own routing catalog overlaid for the 788 models it can actually invoke — where the two sources disagree, the row is flagged with ⚠ rather than silently averaged
• same-model, cross-provider comparison with a cheapest badge: GLM-5.2, say, runs from $3.08 to $4.84 per 1M output tokens depending on the gateway — the same model, 57% apart
• capability tags (coding / agentic / vision / long context / open weights) computed from structured catalog fields, with a user-configurable rule engine
• subscription plans (Coding Plan, Token Plan) grouped separately and excluded from per-token ranking
• a community promotions feed — the part I most want to tell you about, below
• English + Chinese UI (the platform's) plus a Russian pack the plugin itself registers

It installs through the harness's own plugin manager — I never forked anything:

npx -y @deepseek-ai/dsh plugin --profile web add dsh-model-pricing

What surprised me: I built it on a free model

Here's the part I didn't expect. I built the whole thing using DeepSeek
Harness, driven by Qwen3.8-Flash through B.AI's current promotion — the one
the plugin itself ships as a record: "Qwen3.8-Flash API at 0 Credits (free),"
with a source link, a verification date and "end not announced" stamped in.
Total LLM spend for the project: $0. Which made the week a perfect loop —
an agent harness, used to build a plugin about the economics of agent
harnesses, on a free model the plugin advertises.

Eight records shipped on day one; one of them describes the free model that
wrote this plugin's UI.

Numbers, since the internet likes them

priced rows / providers	7,178 / 213
harness-catalog overlaid rows	788 (30 disagreements flagged, not averaged)
plan rows grouped & excluded from ranking	175
promo records at launch	8 (each with source URL + verification date)
commits / files / LOC	28 / 18 / ~2,300
wall-clock	~22h, incl. overnight autonomous rounds
LLM cost	$0 — free API promotion, re-verify date 2026-10-10
UI languages	en + zh (platform), ru (plugin)

Try it — as reviewer and as builder

If you're curious about DeepSeek Harness the way I was: run it, then break into
its settings page. The architecture is the product; the agent is very good at
both jobs, even on a model that costs nothing.

npx -y @deepseek-ai/dsh plugin --profile web add dsh-model-pricing

Repo (docs, feature map, the promotion contribution rules — all public):
github.com/vitas/dsh-model-pricing
· npm:
dsh-model-pricing ·
Apache-2.0.