# Tool presentation: the favourite-index

Big, flat MCP tool catalogs make LLMs **wander** — they call wrong tools before
the right one, or find it then keep exploring. mcpctl (the proxy) decides *what
tool list the model sees*, so presentation is a lever we can pull.

We measured it. On a 145-tool catalog with a wandering model
(`kubernetes-deployment/scripts/model-eval/toolsim.py`), the winning presentation
— **favindex** — nearly halved wander (37→20) and 2.5×'d first-pick (2→5/8) vs the
flat catalog. Enriching descriptions did **not** help; scoping/indexing did.
(Full table + method in the `feedback_llm_tool_scoping` memory.)

## What it does

When enabled for a project, the proxy presents tools in **two namespaces** plus a
**load-bearing instruction**:

- `favourite/<tool>` — a curated, usage-weighted shortlist of the commonly-used
  tools, listed **first**.
- `all/<server>/<tool>` — the **full** catalog (the escape hatch).
- An `initialize` instruction: *"PREFER favourite/<tool> … use all/<server>/<tool>
  only if nothing in favourites fits."*

The instruction is not optional — the same two namespaces **without** it scored
materially worse in the bake-off. Curate **and** tell the model to check
favourites first.

Favourites are a *subset*: leave rare/cloud tools in `all/` only, so the model
falls back correctly for the long tail.

## How it composes

favourite-index is a proxymodel plugin
(`src/mcplocal/src/proxymodel/plugins/favourite-index.ts`) composed **after** the
gate/default plugin:

- While a session is **gated**, only `begin_session` is visible — favourite-index
  no-ops. After `begin_session` ungates, the catalog is reshaped into
  `favourite/` + `all/`.
- Gate/agent virtual tools (`read_prompts`, `propose_prompt`, `agent-<name>`
  chat) pass through unchanged at the top level. Favourites are drawn only from
  the upstream MCP catalog.
- Calls to `favourite/…` / `all/…` are rewritten back to the canonical
  `server/tool` in `onToolCallBefore`, so normal upstream routing **and** the
  content-pipeline (pagination/sectioning) still run.

## Configuring it

Per-project, stored on the project as `favouriteIndex`
(`{ enabled, tools: ["server/tool", …], maxFavourites? }`). Round-trips through
`get project -o yaml | apply -f -`.

```bash
# enable + pin the common tools
mcpctl create project myproj --force --favourite-index \
  --favourite k8s/get_pods --favourite k8s/get_pod_logs \
  --favourite gitea/create_pull_request --max-favourites 15

# what the proxy will present
mcpctl favourites list --project myproj
```

### Deriving favourites from usage

Every tool call is recorded (`AuditEvent` `tool_call_trace`). Rank them and pin
the common ones:

```bash
mcpctl favourites suggest --project myproj --top 20 --window 30
```

This normalizes presented names back to canonical `server/tool` (so `all/…` and
`favourite/…` calls collapse), ranks by call count, and prints a ready-to-run
`create project … --favourite …` line. `★` marks tools already pinned.

## Validating a change first

Before shipping a presentation change, run it through the fake-catalog harness —
it caught "enrichment doesn't help" in ~1h instead of a wasted build:

```bash
toolsim.py <model> favindex all      # vs `terse all` (flat baseline)
```

Then confirm it reproduces through the **real** proxy on a tool-heavy project
(presentation + routing: `src/mcplocal/tests/smoke/favourite-index.test.ts`).
