deer-flow/examples/deerflow-extension-example

DeerFlow extension example

This directory is a compact, standalone Python package showing five of the eight DeerFlow extension contribution kinds: middleware, task lifecycle, system-model observer, service, and router. It depends on the public deerflow-extension-api contract and never imports deerflow.* or app.*.

It does not register an agent-assembly observer, a context-compaction observer, or a full-stack plugin. The observers are covered in the Lifecycle and Observers guide, and deerflow-extension-bookmarks shows a plugin.

The contract package intentionally has no framework dependencies. An extension must therefore declare every framework it imports itself; this example explicitly depends on FastAPI, LangChain, and LangGraph in pyproject.toml.

What it demonstrates

Contribution	Example behavior
Middleware	Counts synchronous and asynchronous tool calls, outcomes, and elapsed time at TOOL_VISIBLE for lead agents and subagents
Task lifecycle	Creates task-scoped stats on start and folds them into app scope on stop
System-model observer	Counts DeerFlow-owned model calls, including failures
Service	Binds ExtensionRuntimeDeps only while the Gateway is running
Router	Eagerly declares GET /api/extension-example/stats during install()

The middleware reads task scope only through task_store_from_runtime(). It passes through unchanged when no task store exists. The router and service use the same ExampleService object: its FastAPI dependency returns 503 before start(), after stop(), or when no app store was bound. This keeps the route topology stable while runtime capabilities arrive later.

Tool statistics

The existing tool_calls field counts calls entering the wrapper. The stats response also includes these fields (this is illustrative output, not a benchmark):

{
  "tool_calls": 3,
  "tool_outcomes": {"returned": 1, "raised": 1, "cancelled": 1},
  "tool_duration_samples": 3,
  "tool_duration_total_ms": 60.0
}

• returned means the downstream handler returned normally, including an error ToolMessage. It does not measure business success. A tool exception converted into a normal return downstream of TOOL_VISIBLE counts here too.
• cancelled counts asyncio.CancelledError escaping the handler, including actual task cancellation. raised counts other escaping exceptions, including LangGraph GraphBubbleUp control-flow signals such as graph interrupts. Results and exceptions propagate unchanged; each wrapper calls its handler once. Resuming an interrupted tool node re-executes it and re-enters the wrapper: the interrupted attempt adds a raised sample, and the resumed attempt adds its own tool_calls increment, duration sample, and outcome. These statistics count observed attempts, not unique logical tool calls across interrupt/resume.
• Each completed observation adds one duration sample, including zero-duration calls. Elapsed time uses a monotonic clock and includes downstream middleware processing. Durations of overlapping lead/subagent calls are summed, so this total is not elapsed run time or exclusive tool execution time.

Outcome counters, duration samples, and elapsed totals are updated together under a lock. Task stats are copied and merged into app scope on task stop, after the task's tool calls have settled. The first stop consumes the task stats; duplicate stops (or a stop without a matching start) add neither tasks nor tool statistics. If a host stops a task while calls are still running, only the snapshot at that stop is merged; later completions are not published. Active tasks are not included in the app's tool totals. The system-model observer retains its existing behavior.

The new fields contain only fixed counters and timing totals, with no tool names, arguments, outputs, exception text, or identifying labels. Stats are process-local and reset on restart; they are not persisted or shared across workers.

Run the package tests

deerflow-extension-api is currently sourced from this checkout. Install it first, then install this independent package:

cd examples/deerflow-extension-example
uv venv --python 3.12
uv pip install -e ../../backend/packages/extension-api
uv pip install -e ".[dev]"
uv run --no-project pytest -q
uv run --no-project ruff check .
uv run --no-project ruff format --check .

The tests use only the public contract plus this package's declared dependencies; the DeerFlow harness and Gateway application are not imported.

Install and load it in DeerFlow

From the DeerFlow checkout root, install this directory through the extension manager. Use an absolute path because the Make wrapper invokes the manager from backend/:

make extension-install SOURCE="$PWD/examples/deerflow-extension-example"
make extension-list

After the trust prompt is accepted, the manager:

• copies a deployable snapshot to backend/extensions/sources/deerflow-extension-example/;
• adds that snapshot to backend/pyproject.toml's extensions dependency group and updates backend/uv.lock;
• installs the locked environment; and
• adds and enables this startup-only entry in the selected config.yaml.

plugins:
  - name: example
    package: deerflow-extension-example
    use: deerflow_extension_example:install
    enabled: true
    required: false
    config: {}

Start or restart DeerFlow after installation:

make dev

The Gateway imports extensions only while constructing the application. Install, enable, disable, remove, and manual plugins: changes therefore take effect only after a restart. These commands manage the example afterward:

make extension-disable NAME=example
make extension-enable NAME=example
make extension-remove NAME=example

The manager can also install a PyPI requirement or a pinned public HTTPS Git URL. SSH Git URLs are rejected because the stock Docker builder does not forward host SSH credentials. The direct CLI surface, run from backend/, is:

uv run --frozen --no-group extensions deerflow extensions install <source> [--yes] [--required]
uv run --frozen --no-group extensions deerflow extensions list
uv run --frozen --no-group extensions deerflow extensions enable <name>
uv run --frozen --no-group extensions deerflow extensions disable <name>
uv run --frozen --no-group extensions deerflow extensions remove <name>

--yes is intended only for automation that has already reviewed and trusted the source: extension build hooks and runtime code execute with Gateway privileges. --required records required: true, which turns any later load failure into a Gateway startup abort; leave it off unless the application is wrong without this extension.

The local snapshot is included in Docker builds. Local make dev, Docker dev, and the production Gateway image all consume the same backend/uv.lock. Development launchers may download missing locked artifacts before handing off to the Gateway; a built production container does not. Rebuild the production image with make up after changing the installed set.

After one or more runs, request the extension route:

curl -s http://localhost:2026/api/extension-example/stats

The response contains aggregated task outcomes, tool-call counts, outcomes and timing, system-model call counts, the app scope id, and a small projection of the host policy. The route passes through the Gateway's normal authentication middleware; use an authenticated browser session when authentication is enabled.

Packaging entry point

Managed packages expose exactly one standard PEP 621 entry point in the deerflow.extensions group. This example declares:

[project.entry-points."deerflow.extensions"]
example = "deerflow_extension_example:install"

The entry-point name (example) is the stable operator-facing name accepted by enable, disable, and remove; those commands also accept the distribution name or the module:install value.

Package layout

deerflow_extension_example/
├── __init__.py  # version-stamped install() entry point
└── plugin.py    # state plus the five demonstrated contribution implementations
tests/
├── test_entry_point.py
├── test_plugin.py
└── test_tool_stats.py