jeff-adapter-tools

Agent tool choice. Picks the next tool for an AI agent to call, or says to answer directly or to ask the user for missing information.

A LoRA adapter for jeff-base v1.3, a small open decision model (a fine-tune of Qwen3.5-0.8B). You send a situation (the state) and questions with named options; Jeff returns a calibrated probability for every option from one forward pass, with no generated text to parse. One Jeff server loads the base once and any number of adapters beside it; each request picks an adapter by name ("model": "tools").

Adapter page, with the full data card: jeffhub.ai/adapters/tools.

Results

On this adapter's held-out test set, never trained on, scored three ways on the same rows: the untrained model Jeff is built from, the Jeff v1.3 base alone, and the base with this adapter. Questions have 4 to 136 options. As of 2026-10-05. All adapters

Each cell: accuracy · calibration error (ECE; lower is better, 0 is perfect).

With llama.cpp (GGUF)

The same test, through llama.cpp: the base GGUF (mstrasser/jeff-base-gguf) plus this adapter's LoRA GGUF (mstrasser/jeff-adapter-tools-gguf), with the temperature refitted for each format. Running Jeff with llama.cpp

Not measured yet for v1.3: calibration charts, the commonest confusions and accuracy per answer. External benchmarks: BFCL v3, multiple and irrelevance; When2Call, test.

Source of these numbers: results/sources/v1.3/retrained-adapters.table.json in the JeffHub repository, also collected in jeffhub-v1.3.json.

When to use it

• Your agent has a list of tools and must decide, at the start of each turn, which one to call next.
• You want a quick first decision with a probability, so a low-confidence turn can be passed to a larger model.
• Your tool list is your own; the adapter reads each tool's signature and description (2 to 150 tools in training).

When not to use it

• You need the tool's arguments filled in. The adapter picks one tool; it does not write the call.
• The task needs several tools in a row. The adapter chooses only the next step; ask again after each call.
• Your tool list is so long that the request would pass 8,192 tokens, the longest row in training.

How to use it

The adapter runs with Jeff's server, on the main branch of firelex/jeff, on the jeff-base v1.3 base.

git clone https://github.com/firelex/jeff && cd jeff
uv sync --no-default-groups --extra lora          # add --extra cuda on NVIDIA GPUs, --extra mac on Apple silicon
uv run --no-default-groups hf download mstrasser/jeff-base --revision v1.3 --local-dir checkpoints/jeff-base
uv run --no-default-groups hf download mstrasser/jeff-adapter-tools --revision v1.3 --local-dir adapters/tools
JEFF_CHECKPOINT=checkpoints/jeff-base JEFF_ADAPTERS=adapters/ PORT=8765 \
  uv run --no-default-groups jeff-serve          # on a Mac, add JEFF_BACKEND=mlx

Every folder in adapters/ is served under its folder name; add or replace adapters while the server runs with curl -X POST http://localhost:8765/v1/adapters/reload. Each adapter records the exact base it was trained on, and the server refuses an adapter trained on a different one, so this adapter loads only on jeff-base v1.3 (a v1.2 adapter does not load on v1.3). For llama.cpp, use mstrasser/jeff-adapter-tools-gguf.

Request format

State (the situation), in this order:

Questions:

• tool (choice): Which tool the agent should call next, or whether to answer directly or ask the user for missing information first. Options: answer_directly and ask_user first, word for word, then your tools as t1, t2, … with each tool's signature and a one-line description.

Rules:

• Keep answer_directly and ask_user as the first two options, with exactly the wording in the example.
• List your tools after them in a fixed order so the unchanging part of the request can be prepared in advance.
• Choose answer_directly also when the user asks for something no tool can do; the agent then explains that it cannot.
• Use the instructions below word for word; the adapter was trained mostly on them.

General rules for every request: the request format guide.

Example

The request below is also in this repository as example.json.

{
  "model": "tools",
  "state": {
    "agent": "An assistant that manages the calendar and email of a small design studio.",
    "conversation": [
      {
        "role": "user",
        "text": "What's on my calendar tomorrow?"
      },
      {
        "role": "assistant",
        "text": "Tomorrow you have a client call with Harbour Books at 10:00 and a team review at 15:00."
      }
    ],
    "user_message": "Please move the team review to Friday at the same time."
  },
  "questions": {
    "tool": {
      "type": "choice",
      "instructions": "Which tool should the agent call next to handle the user's latest message? Use the conversation for context. If no tool is needed, choose answer directly. If a tool is needed but information it requires is missing, choose ask the user.",
      "criteria": {
        "answer_directly": "No tool is needed: answer the user directly from the conversation",
        "ask_user": "A tool is needed but required information is missing: ask the user first",
        "t1": "list_events(date): list the calendar events on a given day",
        "t2": "create_event(title, start, end, attendees): add a new event to the calendar",
        "t3": "move_event(event_id, new_start, new_end): move an existing event to another date or time",
        "t4": "send_email(to, subject, body): send an email now",
        "t5": "draft_email(to, subject, body): save an email as a draft without sending it"
      }
    }
  }
}

curl -s localhost:8765/v1/systemone -H 'content-type: application/json' -d @adapters/tools/example.json

The answer holds a probability for each option of each question. A recorded response from the v1.3 adapter is not published yet.

Files

• adapter_model.safetensors, adapter_config.json: the LoRA weights (PEFT format);
• readout.safetensors: the adapter's own readout over the answer codes;
• decision_config.json: answer codes, temperature, prompt layout and the checksum of the base it was trained on;
• test.jsonl: the held-out test set the results below were measured on;
• calibration.jsonl: the calibration rows the adapter's temperature was fitted on;
• example.json: the example request above.

adapter_config.json and decision_config.json name the base as mstrasser/jeff-base, revision v1.3; the server checks the base by the checksum of its weights.

Training

• 1.3.0 (2026-10-03): Trained on Jeff v1.3 with the live-last prompt layout (LoRA rank 16, one epoch, about 10% of the base model's own training data mixed in).

Data card

Report attached. The shortcut report and data card are included and pass the JeffHub checks; the numbers are the maintainers’ own. What the levels mean

• Test set: included in this repository as test.jsonl, so anyone can check the numbers
• Calibration rows: included in this repository as calibration.jsonl, the rows its threshold is chosen on
• QA report, sanitised: the data-quality checks run before training

How the test set was held out. Requests to the 10% of the roughly 450 generated agents that were never trained on.

Training data. Training data not published.

Which models made the data, counted on the 39,203 training rows:

Counted from each row's own record of the models that made it (the field named under each job). A row counts once under every job that names a model, so the counts do not add up to the total.

The terms of the hosted model providers are being checked for training and publication use.

Training mixed in a replay sample of the Jeff base model's own training data: 3,920 rows, about 10% on top of the adapter's 39,203 (inherited from the v1.2 recipe as a precaution; its effect has not been measured).

Data and licence

Adapter licence: Apache-2.0.

Qwen3.5-0.8B notice: these weights were modified from Qwen3.5-0.8B by the Jeff project: jeff-base is a fine-tune of Qwen3.5-0.8B, and this adapter was trained on top of it. Qwen3.5-0.8B is Copyright 2026 Alibaba Cloud and licensed under the Apache License, Version 2.0; a copy of that licence is in LICENSE.

It was trained on:

• Generated agents, tool sets and user messages. Licence: Released with the adapter under Apache-2.0 (made for this adapter) · Made by Qwen3.8-Max (hosted) and Qwen3.8-Flash-Next (local); see the data card

  About 450 agents with their tool lists (including deliberate near-duplicate tools) and 39,203 training rows, written by language models and checked by code and a second pass (which models, and for how many rows, is in the data card).

Limitations

• Tied to jeff-base v1.3. It will not load on any other base or version; the server checks the base weights' checksum.
• Jeff chooses between the options you give it. It does not write text or reason in several steps.
• Calibration was fitted on this adapter's own calibration rows. On very different data, check it again.
• Everything listed under When not to use it above.

Links

• Adapter page: jeffhub.ai/adapters/tools
• Base model: mstrasser/jeff-base (revision v1.3)
• LoRA GGUF for llama.cpp: mstrasser/jeff-adapter-tools-gguf
• What changed in v1.3: release notes
• Code and server: github.com/firelex/jeff

Jeff is an independent project. It uses the same request format as Jev but is not affiliated with or endorsed by TypeSafe, the makers of Jev.