dsh-tool-index

75 MCP tools connected, one small task: 183,274 tokens without this plugin, 79,838 with it — 56% less.

dsh-tool-index sends your MCP tool definitions as a compact index and loads full schemas only when the model asks for them. The tool list itself never changes mid-session, so your prompt cache keeps working.

A plugin for DSH. Built on DeepSeek Harness; not an official DeepSeek project.

The problem

Every tool definition is sent again on every model request. Connect a few MCP servers and an agent carries hundreds of definitions it never uses: thousands of tokens on every step, and a model that picks tools worse because it has too many to choose from.

What it does

dsh-tool-index sends those tools as a short index instead: each tool's name, parameters and one-line summary, grouped by server. When the model needs one, it reads the full details with tool_details and runs it with call_tool.

without:  read, bash, mcp__github__create_issue {full schema}, mcp__github__list_issues {full schema}, ... ×180
with:     read, bash, tool_details {index: 180 names + one-liners}, call_tool

• Fewer tokens on every request. The MCP tools cost about 88% less per request.
• The prompt cache keeps working. The tool list stays the same for the whole session, so loading a tool never forces the provider to re-read the conversation at full price.
• The model doesn't miss tools. Every tool is always named in the index, and a wrong name (a typo, a missing mcp__server__ prefix) gets the closest real names back.
• Nothing is bypassed. Permission policies, approvals and hooks still see the real tool and its arguments.

Does it save tokens?

Yes. One small task, three runs per cell, with real MCP servers:

Model	Without the plugin	With it	Change
DeepSeek deepseek-flash, 25 MCP tools	80,777	58,864	-27%
DeepSeek deepseek-flash, 75 MCP tools	183,274	79,838	-56%
Claude claude-haiku-5-5, 25 MCP tools	110,598	94,422	-15%
OpenAI gpt-5.4-mini, 25 MCP tools	50,846	23,398	-54%

And over a 5-message conversation in one session (DeepSeek, two of the messages need no tools):

Servers	Without the plugin	With it	Change
25 MCP tools	159,736	106,398	-33%
75 MCP tools	317,040	147,120	-54%

Tokens summed over every model step. Every run finished its task with and without the plugin. The more tools you connect, the more it saves.

Reproduce them yourself with e2e/run.sh.

Install

As a bundle in a profile:

dsh plugin --profile tui add dsh-tool-index
dsh --profile tui

Or from a checkout, for one run:

git clone https://github.com/GunjanPatel359/dsh-tool-index
cd dsh-tool-index
dsh tui --patch ./examples/local.patch.yml

Configuration

- id: dsh-tool-index
  name: dsh-tool-index
  config:
    match: ['mcp__']          # MCP name prefixes to defer
    exclude: []               # ...except these prefixes, e.g. ['mcp__mycore__'] for tools used every turn
    alwaysLoad: []            # exact names always sent in full
    minTools: 10              # defer only when at least this many match
    indexStyle: signature     # names | summary | signature (name, parameter names, summary)
    maxDetails: 10            # most tools one tool_details call returns
    summaryChars: 120         # length of each summary in the index
    indexChars: 12000         # past this, remaining tools are listed by name only
    detailsToolName: tool_details
    callToolName: call_tool

A patch replaces a row's whole config, so restate every key you set.

With fewer than minTools matching tools nothing changes: a handful of definitions costs less than an extra step.

Keep tools the agent uses on most turns out of the index with exclude or alwaysLoad.

This plugin is for MCP tools. match takes name prefixes, but deferring your harness's own core tools (read, bash and the like) will make the agent worse, not cheaper: it needs them on almost every turn, and there is no guard against it.

Trade-offs

• Sometimes one extra step (tool_details) before a deferred tool is first used in a conversation.
• Arguments are checked by the tool, not by the provider. A wrong argument comes back as the tool's own error.
• UIs show call_tool as the outer step, with the real tool inside it.

Compatibility

• Native tool calls: the mode the plugin is built for.
• PTC mode (run_code): the plugin steps aside for those agents and adds nothing to their requests. In PTC mode the model calls tools from code, and DSH already lists every tool for that code.
• Sub-agents and structured-output children: each agent gets its own index of its own tools. A child's structured_output tool stays a normal tool.

Written for DSH 0.2.x. DSH is pre-1.0, so its plugin interfaces can change between releases.

How it works

• docs/how-it-works.md — the index, tool_details, call_tool, and why the tool list stays fixed.
• docs/name-matching.md — how a wrong tool name is matched to the closest real one.

License

MIT