dsh-lean-mode
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A DeepSeek Harness plugin that presents every tool to the model in a lean, executable form — install it and it just works, remove it and the old form is back. No core changes.
The problem
Tool schemas are sent on every request. In a deployment with hundreds of MCP tools they dominate the context:
| Deployment | Tools | Tool schemas | Share of the first request |
|---|
Default standard preset (measured on a real deployment) | 84 | 89 KB | ~22,300 of 36,264 tokens — 61.6% |
| All MCP tools mounted | 731 | 988 KB | ~275,000 tokens — 27.5% of a 1M window |
Most of that is JSON-Schema punctuation the model rarely needs: nested descriptions, deep objects, defaults. The names and the top-level contract are what make a call possible.
What this plugin does
Two things, per assembly:
- Shrinks each tool's parameter schema to its top-level contract — top-level keys,
required, each key's type
and a short enum when declared. Nested structure, descriptions and defaults are dropped.
- Appends a
tools:catalog prompt section listing every tool — including the ones the model is unlikely to recall — with the exact argument envelope and a one-line purpose.
Why the envelope must survive
In a real catalogue 64% of tools take a single required wrapper key (commonly params). Collapse the schema to an open {type:'object'} and the model flattens the arguments, so every call is rejected:
| Channel shape | Calls that actually execute |
|---|
Open skeleton additionalProperties: true | |
| 1.7% | |
| Top-level contract kept | 95.0% |
Measured effect
Same model, same 199-task set, same catalogue:
| Tools | Baseline (full schemas) | lean | Ratio |
|---|
| 26 | ~5,340 tok | ~2,385 tok | 0.45 |
| 84 (a real deployment's default preset) | ~22,300 tok | ~9,400 tok | 0.42 |
| 731 (every MCP tool) | ~275,000 tok | ~68,000 tok | ★ 0.247 |
End-to-end callability (tool name in the catalogue and the emitted arguments satisfy the real schema):
| Presentation | End-to-end |
|---|
| Full JSON Schema | 95.0% |
| lean | 89.9% |
| Open skeleton only | 1.7% |
Install
From GitHub (verified end to end: installed this way, the mode appears in the UI preset menu and takes effect)
dsh plugin --profile web add github:q862877400-ux/dsh-lean-mode
From a local checkout
dsh plugin --profile web add <path to this directory>
Uninstall
dsh plugin --profile <profile> remove @local/dsh-lean-mode
The bundle carries both the plugin row and a Lean mode preset declaration, so once installed the mode appears in the UI's preset menu; removing the bundle removes both.
How it works
system-prompt/assemble is a waterfall whose contract states the returned value is authoritative, and scoped listeners receive only that scope's assemblies. This plugin therefore:
- registers a profile-level listener, so it sees every assembly;
- asks
agentPresets.composedPreset(agent.ctx) which preset the assembly's agent runs under;
- transforms only when that preset is one it was configured for.
export function apply(ctx, config) {
const wanted = config?.presets // e.g. ['lean']
ctx.on('system-prompt/assemble', async (assembly, context, next) => {
const base = await next()
if (wanted && !wanted.includes(presetOf(ctx, context?.scope))) return base
return { ...base, tools: base.tools.map(toShallow), sections: [...base.sections, catalog] }
})
}
It uses only upstream APIs — no new tools.mode value, no patched package.
Configuration
| Key | Default | Meaning |
|---|
presets | undefined | Preset ids this applies to. Omit to apply to every session. |
shape | true | Project parameters to the top-level contract. |
catalog | true | Append the tools:catalog section. |
Limitations
- ★ All figures were measured on one local deployment (731-tool catalogue unioned from real sessions; 199 tasks; a single model). Ratios will differ elsewhere — re-measure before relying on them.
- ★ Callability is judged as "the emitted call is valid against the real schema", not "the tool succeeded on a machine".
- ★ End-to-end accuracy (89.9% vs 95.0%) is a single-run figure on that task set.
- ★ The catalogue repeats each tool's one-line purpose, so the win grows with the size of the parameters, not merely the count of tools.
License
MIT. See LICENSE and THIRD-PARTY.md — cordis.patch.yml restates a preset composition from DeepSeek Harness (MIT, Copyright (c) 2026 DeepSeek); the plugin source is original.
