DecisionNode Python SDK

DecisionNode is a decision engine: send it text, JSON or images with a question, and it answers with calibrated probabilities.

The official Python client for the DecisionNode API: ask yes-or-no, multiple-choice, scale and number questions about any text, JSON or image, and get calibrated probabilities back. One request at a time, a live session answering a stream of frames, or a batch of thousands at the batch price. Sync and async clients, fully typed.

Install

pip install bynn-decisionnode

or uv add bynn-decisionnode. Python 3.10 or later.

Set your API key

export DECISIONNODE_API_KEY="your-api-key"

A key's kind decides what it may call: Full access for your servers, Decisions only for a device or a service that only decides, Manage device keys for the server that hands out device keys, and Publishable for a web page or an app. See API keys.

Quickstart

from decisionnode import DecisionNode, truth, choice, score

dn = DecisionNode()  # reads DECISIONNODE_API_KEY

d = dn.decide(
    state={"ticket": "I was charged twice and nobody has replied for 3 days."},
    questions={
        "route": choice("Where should this go?", {"billing": "money", "bug": "broken", "account": "login"}),
        "urgency": score("How urgent is this?", ["routine", "today", "urgent", "critical"]),
        "escalate": truth("Escalate to a human now?"),
    },
)

d["route"].choice  # "billing"
d["route"].probabilities  # {"billing": 0.87, "bug": 0.08, "account": 0.05}
d["urgency"].score  # 2.31
d["escalate"].truth  # 0.94

The same with asyncio:

import asyncio
from decisionnode import AsyncDecisionNode, truth


async def main() -> None:
    async with AsyncDecisionNode() as dn:
        d = await dn.decide(state="Refund my order now!", questions={"angry": truth("Is the customer angry?")})
        print(d["angry"].truth)


asyncio.run(main())

Questions

Six question types. Each builder returns the question in its wire form, and a plain dict in that form is accepted anywhere a builder is.

state, instructions, option descriptions and levels take a string or any JSON-serialisable value. Question ids are any string and come back unchanged; read answers by id, never by position.

truth("Is this a refund request?", if_true="the customer asks for money back")
choice("Which language is this?", ["en", "de", "sv"])
score({"question": "How complete is the form?", "focus": "required fields"}, ["empty", "partial", "complete"])
number("How many cars are visible?", min=0, max=50)
number("Rating in halves?", min=0, max=5, step=0.5)

A number grid holds at most 4,096 values, with at most 6 decimals in min and step. number leaves out of the request any of min, max and step you do not give, so the API's defaults apply.

The values are the ones the API sent: probabilities are not rounded or renormalised, so a list can sum to 0.99 or 1.01, and an entry can read 0.8200000000000001. An answer of a type this version does not know comes back as UnknownAnswer with its fields in .raw, and so does an answer of a known type with a missing or wrongly typed field; the rest of the decision parses as usual.

One question at a time

dn.check("Package arrived crushed.", "Is the customer reporting damage?").truth  # 0.97
dn.classify("Where is my parcel?", "Topic?", ["shipping", "billing", "returns"]).choice  # "shipping"
dn.score("Site is down for everyone!", "Severity?", ["low", "medium", "high"]).score  # 1.86

dn.number("Drone frame over row B4.", "How many cars?", min=0, max=50).number  # 7

check(state, instructions, if_true, if_false), classify(state, instructions, options), score(state, instructions, levels) and number(state, instructions, min, max, step) send one question and return its answer. Like decide, each of them and gate also take images= and model=. They promise a typed answer, so when the server's answer to their question is missing or malformed they raise ServerError (status 200, reason from x-decisionnode-error), where decide would return the same answer as UnknownAnswer.

gate(action, context) judges an action before it runs. It sends the state {"action": ..., "context": ...} and three questions, worded the same in every official DecisionNode SDK, and returns the Decision:

g = dn.gate("DROP TABLE invoices;", {"environment": "production"})
if g["verdict"].choice != "allow":
    ask_a_person()

The thresholds are yours: the SDK never turns a probability into a decision.

The decision

Many requests

from decisionnode import DecisionNodeError

results = dn.decide_many(
    [{"state": t, "questions": {"spam": truth("Is this spam?")}} for t in tickets],
    concurrency=8,
)
for r in results:
    if isinstance(r, DecisionNodeError):
        print("failed:", r)
    else:
        print(r["spam"].truth)

At most concurrency requests run at once (default 8; below 1 raises ValueError before anything is sent). Every request is checked before the first is sent, so a bad argument in any of them raises ValueError, a request the API would refuse raises its error class, and nothing is sent. Results come back in input order, one DecisionResult per request: a Decision, or the error that request ended with. Images with the same bytes are uploaded once for all the requests. One failure does not stop the others.

Images

from decisionnode import Image

d = dn.decide(
    state={"claim": {"total": "740.00", "currency": "SEK"}},
    images=[Image("receipt", url="https://files.example.com/claims/4411/receipt.jpg")],
    questions={"total_matches": truth("Does the total on the receipt equal the total in the claim?")},
)

Send images by URL when you can. It is the fastest input: nothing is uploaded, the request stays small, and the server fetches the image while it reads the request. A URL must be https and at most 2,048 characters.

The other forms:

Local images (a path or data) are checked before anything is sent, without decoding them: JPEG, PNG or WebP by their first bytes (a media_type you give must match them), at most 10 MB each, at most 40 megapixels, read from the image's header. A file that cannot be read raises ValueError when the Image is made; an image the API would refuse raises BadRequestError before any request. A request holds at most 16 images, URLs included; a 17th raises ValidationError before any request, as the API answers it (a too_long entry on the images).

How local images travel is chosen for speed:

• When the local images of a request total under the inline threshold (512 KiB, DEFAULT_INLINE_THRESHOLD; set inline_threshold on the client to change it) they go inline in the request.
• At or above it they are uploaded first: one POST /v1/uploads for all of them, then one PUT each, in parallel, straight to storage, and the request names them by upload_id. The PUT carries only the headers the upload was signed with: never your key, never your custom headers.
• The client remembers what it uploaded, by the SHA-256 of the bytes, for as long as the upload lives (until 5 minutes before it expires, at most 256 images). The same image sent again, in another call, in decide_many, in a session frame or a batch line, goes by its upload_id whatever its size, without being uploaded again. When the server reports such an upload as expired or gone, the client uploads the image again and sends the request once more.

A request body may be at most 25 MiB (26,214,400 bytes). Inline images count toward it; uploaded images and URLs do not. The client measures each request as it will be sent, decide_many requests and batch lines included, and raises RequestTooLargeError before anything is sent or uploaded when it is over. Images given as a path or bytes above the inline threshold are uploaded, so only a large state or base64 data you send yourself can reach the limit.

An Image can be reused across calls; its checks and hashes are computed once.

Upload ahead

upload_ids = dn.upload([Image("front", path="front.jpg"), Image("back", path="back.jpg")])
d = dn.decide(state="...", images=[Image("front", upload_id=upload_ids[0])], questions={...})

upload(images) uploads 1 to 16 images whatever their size and returns one upload_id per image. An upload can be used for one hour by any key of your workspace.

Referring to images and videos

There are two ways to say which image a question is about:

1. By id (recommended). Give each image a short, meaningful id and use it in the instructions, in backticks: "Does the total on receipt match the amount in the claim?"
2. By number. Images are numbered from 1 in the order of images: "image 2", "the second image", "Picture 2" and "the last image" all work.

The model sees each image as Picture 1 (receipt):, Picture 2 (claim_photo):, so both ways point to the same image. Prefer ids: they stay right when images are added or reordered. Use names, not digits, as ids (front, not 2). Videos work the same way, by id or by number ("video 1"), numbered separately in the order of videos. The image of a point or box question takes the id.

d = dn.decide(
    state="Expense claim 4411: 740.00 EUR.",
    images=[
        Image("receipt", url="https://files.example.com/claims/4411/receipt.jpg"),
        Image("claim_photo", url="https://files.example.com/claims/4411/photo.jpg"),
    ],
    questions={"matches": truth("Does the total on `receipt` match the amount in the claim?")},
)

Points and boxes

A point question finds one spot in an image; a box question draws a rectangle around something. They mix freely with the other types in one request, and several of them on the same image share one read of it.

from decisionnode import Image, box, point, truth

d = dn.decide(
    images=[Image("belt", url="https://files.example.com/line-3/cam-2/0917.jpg")],
    questions={
        "pick": point("Point to the yellow package closest to the robot arm."),
        "damage": box("Draw a box around the damaged package.", image="belt"),
        "any_damage": truth("Is any package on the belt damaged?"),
    },
)

pick = d["pick"]
if pick.present > 0.8 and pick.confidence > 0.7:
    robot.pick(pick.x, pick.y)
else:
    send_to_operator()

Every field is always there. When several things match, the answer is the best match; say which one you mean in the instructions ("the leftmost yellow package").

A point or box question needs an image in the request. With two or more images, name the one to look in with image, the image's id; a reference by number ("Picture 2") goes in the instructions. These rules and units ("pixels" or "normalized") are checked before anything is sent, and a fault raises ValidationError as the API would. decide, decide_many and batch requests take point and box questions.

Videos

A video is sent as the frames you sampled, each with its time in seconds, and the questions see them as one video, in order and with their times. Only frames are sent: no video file, no video URL and no sound go to the API.

from decisionnode import VideoFrame, Video

frames = [VideoFrame(t, jpeg) for t, jpeg in camera_frames]  # (seconds, JPEG bytes) you already hold

d = dn.decide(
    state="Warehouse camera 4, loading dock, shift B.",
    videos=[Video("dock", frames, fps=2)],
    questions={
        "fall": truth("Does a person fall in the video?"),
        "forklifts": number("How many forklifts pass the door?", min=0, max=50),
    },
)
d["fall"].truth
d.usage.video_frames, d.warnings

The ids, times, media types, fps and the window are checked before anything is sent, and a fault raises BadRequestError as the API would. A request holds at most 4 videos; a fifth raises ValidationError (a too_long entry on the videos). The frame limits are the API's and are published with it. Frames always go inline: they are never uploaded or resized. decide, the helpers, decide_many and batch requests take videos; sessions do not.

To turn a video file into frames, use the dn command-line tool (dn truth "Does a person fall?" --video dock.mp4 --fps 2); it runs FFmpeg on your machine and sends only the frames. This package has no such dependency.

Boosters

A booster is a specialist model that reads the request's images before the decision. Its reading is added to what the model sees, and comes back in evidence. The model still answers every question: a booster never answers one, and a request without boosters is answered exactly as before.

from decisionnode import Image, truth

d = dn.decide(
    images=[
        Image("a1b2", url="https://files.example.com/a1b2.jpg"),
        Image("c3d4", url="https://files.example.com/c3d4.jpg"),
    ],
    boosters=["age", "ai_generated"],
    questions={
        "adult": truth("Is the person in the first picture an adult?"),
        "synthetic": truth("Is the second picture AI-generated?"),
    },
)

d["adult"].truth  # 0.97
age = d.evidence["age"]
age.status, age.version  # "ok", "age-v3"
age.results[0].age_years, age.results[0].low, age.results[0].high  # 27, 22, 33
d.evidence["ai_generated"].results[1].generated  # 0.93
d.usage.booster_tokens, d.usage.boosters  # 72, 4

boosters is a list of booster names, in the order you want them reported. decide, the helpers, decide_many requests and batch requests take it. Sessions do not.

A booster that needs a setting is a Booster. Here ai_generated reads only the second picture, and the request fails if it cannot:

from decisionnode import Booster

d = dn.decide(
    images=images,
    boosters=["age", Booster("ai_generated", images=["c3d4"], require=True)],
    questions=questions,
)

It is sent as {"name": "ai_generated", "images": ["c3d4"], "require": true}, each setting only when given; a plain mapping in that form works too. A Booster with no setting is sent as its name, so the request stays the plain list.

The client checks nothing about boosters itself: the API answers a malformed list, an unknown name and a booster turned off for your workspace before any booster runs and before any charge. A booster added to the API works with this version of the package.

A request whose boosters name ocr waits 30 seconds per attempt by default; a timeout you set on the client is used as given. It is never retried after a timeout, because the server finishes that attempt and may bill it: set a timeout of at least 30 seconds for such requests.

d.evidence maps each booster the request named, in its order, to an Evidence:

Booster calls are billed from your prepaid balance with the request's tokens, one per booster and image read with status ok: a booster that timed out or failed is free, and so are the boosters of a refused request. The readings' tokens are input tokens at the model's price. The price per call is on the pricing page.

Every error of a request that named boosters carries e.boosters: what each booster did, in the request's order, as booster name to BoosterStatus (status, latency_ms), so you can see which required booster failed.

from decisionnode import OverloadedError

try:
    d = dn.decide(images=images, boosters=[Booster("age", require=True)], questions=questions)
except OverloadedError as e:
    if e.error_type == "booster_unavailable":
        print(e.boosters["age"].status)  # "timeout"

Sessions

A session fixes the questions once, then answers every frame you send on a WebSocket, newest first: a frame that arrives while another is being answered replaces any frame still waiting, so you always get the answer to the latest reading, never a backlog.

from decisionnode import DecisionNode, Reply, FrameError, SessionClosed, choice, truth

dn = DecisionNode()
with dn.open_session(
    instructions="You are the mission supervisor of a survey drone.",
    state={"mission": "Survey the north field"},
    questions={
        "mode": choice("Which flight mode now?", ["continue", "hold", "return", "land"]),
        "abort": truth("Should the mission be aborted now?"),
    },
    window=8,
) as session:
    session.connect()
    session.send({"battery": 0.31, "wind_mps": 11.4})
    for event in session.replies():
        if isinstance(event, Reply):
            print(event.seq, event["mode"].choice, event.dropped)
        elif isinstance(event, FrameError):
            print("frame", event.seq, event.error_type, event.message)
        else:  # SessionClosed, the last event
            print("closed", event.code, event.reopen)

A FrameError is a value, not an exception: the session stays open. SessionClosed has the close code and reopen, true when opening a new session with the same arguments is the right next step (1001, 1006, 1011, 4404, 4408, 4409, 4410). A key that already holds its open sessions gets SessionLimitError (a RateLimitError), which is never retried. Pings are answered for you. The async client has AsyncSession, with the same methods as coroutines and async for event in session.replies().

Supervise a feed

def readings():
    while drone.flying:
        yield {"frame": drone.telemetry()}
        time.sleep(1)


last_close = dn.supervise({"questions": questions, "state": mission}, readings(), on_reply=print)

supervise(body, feed, on_reply) keeps one session answering a feed of readings. body holds the open_session arguments, each reading the send arguments, and on_reply gets every Reply and FrameError. When the session closes on a code that calls for it, a new one is opened (at once after the idle and lifetime closes, else after a backoff of 1 to 30 seconds with jitter); on 1013 it connects to the same session again; on any other code it stops and returns that SessionClosed. When the feed ends it waits for the replies still owed, ends the session and returns the last SessionClosed seen, or None. With the async client the feed may be an async iterator and on_reply a coroutine function.

Batches

The Batch API answers many decide requests at the batch price: 50% off the live price on decisionnode-flash, 30% off on decisionnode-moe. The batch price is each model's, its batch_price_factor in models() (0.5 and 0.7; a fine-tuned model's entry states none), never the batch's, and each line's charge is in its usage. There is no set time at which a batch runs or finishes, so poll for it. Requests not answered within 24 hours of finalizing expire and are not charged.

requests = [
    {"custom_id": t.id, "state": t.text, "questions": {"route": choice("Where should this go?", ["billing", "bug"])}}
    for t in tickets
]
batch, results = dn.run_batch(requests, poll_interval=60)
for r in results:
    if r.decision is not None:
        print(r.custom_id, r.decision["route"].choice)
    else:
        print(r.custom_id, r.status, r.error)

run_batch(requests, poll_interval, timeout) creates a draft, adds the requests, queues it, reads it every poll_interval seconds (at least 10; the server's Retry-After when that is longer) until it ends, and returns the ended Batch with its results. Past timeout (default 26 hours) it raises TimeoutError; the batch keeps running. If adding the requests fails, the draft is cancelled and the error raised.

Each request is a decide request plus a custom_id (1 to 512 characters, unique in the batch). Every request is checked before anything is sent; images follow the rules above, per line.

A BatchResult has custom_id, status (the HTTP status, or "expired" or "cancelled"), decision for a 200 line, error for an error line (the exception the live call would have raised, as a value), and headers.

get, list, results and cancel are retried like every call. create, add and finalize change the batch, so they are retried only on 429 and 529, which the API answers before applying anything, and never after a timeout or a lost answer. A finalize answered 409 is checked with get, and the batch is returned when an earlier finalize went through.

Models

for m in dn.models():
    print(m.name, m.release_date, m.limits)

Each entry is a ModelInfo. limits holds every other field the model publishes: the prices (price_per_million_input, price_per_million_output, price_per_million_image, price_per_million_video, in USD per million tokens, and batch_price_factor), the token limit, the number grid limits, the upload limits, and the sessions and batch objects. The five prices are also fields of ModelInfo, as sent, each None when the entry states none (a fine-tuned model states no batch_price_factor).

Choose per client (DecisionNode(model="decisionnode-flash")) or per call (dn.decide(..., model="decisionnode-moe")). Each model publishes its limits in models().

models() also lists the pinned ids served, decisionnode-<family>-<version> (such as decisionnode-moe-<version>); send one to stay on that release. Every answer's model is the pinned id that answered. model is free text: a pinned id, a fine-tuned name and the older ids the API still accepts (decisionnode-1.0, decisionnode-1.0-flash, decisionnode-latest, decisionnode-flash-latest) are sent as given.

Fallback

A request for decisionnode-moe that no worker of that model can take at once is answered by Flash instead, billed at its price. d.model is the model that answered, and d.fallback names both: the model that answered by its pinned id, and the model asked for as it was asked (a family id or an older id as the family id, a pinned id as itself):

d = dn.decide(state=ticket, questions=questions, model="decisionnode-moe")
if d.fallback is not None:
    d.fallback.served_model  # "decisionnode-flash-<version>"
    d.fallback.requested_model  # "decisionnode-moe"

fallback=False turns it off for one request: such a request gets the 529 OverloadedError instead, which is retried like every 529. decide, the helpers, decide_many requests and batch requests take it; left out, the API's default (on) applies. Sessions, batch lines and fine-tuned models never fall back.

Fine-tuned models

A model your workspace trained in the console is called by its name, by your workspace's keys only, and answers like its base: the same question types, answers, limits and errors.

d = dn.decide(state=claim, questions=questions, model="decisionnode-moe@acme/fraud")
d.model  # "decisionnode-moe@acme/fraud:3", the version that answered

The name is <base>@<workspace>/<name>, which means the version deployed most recently, or <base>@<workspace>/<name>:<n> for version n. The client sends it as given; a name that does not exist, a version that is not deployed and another workspace's model all raise BadRequestError (Unknown model: <name>). Decision.model is always the pinned name, so you can log which version answered.

models() lists your workspace's fine-tuned models beside the catalogue's, each with fine_tuned (True), base (the base model), adapter_version (the version number) and status (deployed, which answers decisions, or ready: trained and not deployed). On the catalogue's own entries these four are None.

Collections

A collection holds faces your workspace enrolls, each with your own reference, an optional label and metadata, so a face_recognition booster can find them in the pictures of a decision. Every call returns the API's object as sent.

col = dn.collections.create("Staff")
item = dn.collections.enroll(
    col["id"],
    Image("badge", url="https://files.example.com/staff/1042.jpg"),
    reference="employee-1042",
    label="Front desk",
    metadata={"site": "north", "shift": 2},
)
dn.collections.update_item(col["id"], item["id"], label=None)  # clears the label
page = dn.collections.list_items(col["id"], reference_prefix="employee-")

A reference is 1 to 64 of A-Z, a-z, 0-9, _, ., : and -, a label 1 to 128 characters. metadata is an object of up to 20 keys, each 1 to 40 of a-z, 0-9 and _, whose values are texts of up to 500 characters, numbers or True/False. These are checked before anything is sent. create, enroll and update_item send an Idempotency-Key, the same on every attempt of a call, so a retried call creates, enrolls or edits once.

Device keys

A Manage device keys key, kept on your provisioning server, makes a Decisions-only key for each device as it enrolls, and changes or revokes it later. Every call returns the API's object as sent.

import os

admin = DecisionNode(api_key=os.environ["DECISIONNODE_MANAGE_KEY"])

created = admin.keys.create(
    "Kiosk 0412",
    device_id="kiosk-0412",
    labels={"store": "118", "fw": "2.4"},
    limits={"requests_per_second": 5, "tokens_per_second": 20000},
    daily_spend_cap={"usd": 2.0},
    idempotency_key="enroll-kiosk-0412",  # a retried enrollment gets the same key back
)
secret = created["secret"]  # hand it to the device once; never log it

admin.keys.update(created["key"]["id"], labels={"store": "120"})
while admin.keys.revoke_by_labels({"store": "118"})["more"]:
    pass

create sends an Idempotency-Key: yours when you pass one (one per enrollment), else a new one per call, the same on every attempt, so a retried call makes one key. A retry with the same key and body within 24 hours returns the same key and secret.

What the API checks by fixed rules is checked before anything is sent, with its messages: a key's name (1 to 48 characters once trimmed), a device_id (1 to 128 printable ASCII characters, not starting with a space), labels (at most 16, each name 1 to 32 of a-z, 0-9, _, . and -, each value 1 to 64 characters), limits being an object, a daily_spend_cap from USD 0.01 to 1,000 in whole cents, an update with nothing to change, a bulk revoke without a label or with over 1,000 device_ids, and list's filters and limit. A limit's ceiling (your workspace's own), the expiry's window and a name's characters are the API's to judge. The whole flow is in Keys on devices.

Per-key usage

What each key used and cost over a period: a Full access key reads every key of its workspace, a Manage device keys key its Decisions-only keys. Every call returns the API's object as sent.

one = dn.usage.key("key_7c2e9a41b0d34f6e8a5c1d2b3e4f5a60", granularity="day")
items = dn.usage.all(
    "2026-10-01T00:00:00Z",
    "2026-11-01T00:00:00Z",
    labels={"customer": "acme"},
    status="all",
)
for item in items:
    print(item["key"]["name"], item["totals"]["cost"]["usd"])

start and end are RFC 3339 times, rounded to the hour. granularity (none, hour, day or month) adds buckets, and group_by (model or channel) by_model or by_channel. labels keeps the keys with all of them, key_ids (at most 100) the keys named, scope (full, decide or keys) and status (active, expired, revoked or all) the keys of that kind or state; include_empty=True lists keys with no usage too; limit is 1 to 1,000. A page can hold fewer keys than limit, so only next_cursor says when the list is done: all follows it for you. These query rules are checked before anything is sent, with the API's messages; the period's own rules are the server's. See Usage.

Errors

Every error derives from DecisionNodeError, with status, error_type, request_id, boosters (for a request with boosters, what each booster did; an empty mapping otherwise), details (the error body's detail.details when it is an object, such as {"reason": "enrollment_unpriced"}; None otherwise) and reason: the server's explanation in words, from the x-decisionnode-error header, for example question 'q': a score takes up to 10 levels, got 11. The error's own message, str(e) (also e.message), is the server's message exactly ("" when the server sent none, never None), or the client's description when no response arrived.

An error whose body is not JSON (a page from a proxy or the service's edge, or no body at all) is classed by its status alone, as in the table: a 400 is a BadRequestError, a 403 a PermissionDeniedError, a 422 a ValidationError with no entries. Its error_type is None, request_id and reason come from the response headers when it has them, and the page is never read: the message is the client's own, HTTP <status> <text> (for example HTTP 413 Content Too Large), followed by (request id <id>) when the response has an x-request-id. It is retried as any other error of its status: a 408 is, a 413 is not.

from decisionnode import DecisionNodeError, ValidationError

try:
    dn.decide(state="...", questions={"q": score("Rate it", levels)})
except ValidationError as e:
    print(e.entries)
except DecisionNodeError as e:
    print(e.status, e.reason, e.request_id)

ConnectionError and TimeoutError here are the classes of this package, not Python's built-ins of the same name.

A problem with an argument is found before anything is sent and raises Python's own ValueError, never a DecisionNodeError: an empty question map, a value that cannot be sent as JSON, a file that cannot be read, a base_url that is not https, a timeout that is not above 0 or a negative max_retries.

A request the API would refuse by its fixed rules is refused before anything is sent too, so the server never sees it. The error is the one the API would answer with (the same class, error_type, message, and for a ValidationError the same entries), but with no status and no request_id. The checks run in the API's order:

• more than 128 objects and arrays inside each other (BadRequestError, "Invalid request.");
• a body over 25 MiB as it will be sent (RequestTooLargeError, error_type request_too_large_error);
• the shape of each question and of the state (ValidationError): a question that is not an object or has no type, values that must be a string, an object or an array, a choice or score without criteria, a score without levels, and every number grid rule;
• the question limits (BadRequestError): an unknown type ("Invalid request."), a choice without options or with more than 255, a score with more than 10 levels, a truth question with neither instructions nor criteria, a number question without instructions;
• every image rule above, an id for each image of at most 64 characters (counted as characters, not bytes: "Image 1: its id is longer than 64 characters."), each id used once, and for a URL: https, at most 2,048 characters, no user information, port 443, not a literal private address (image_url_refused);
• for sessions, window (1 to 64) and ttl_seconds (1 to 3,600) as ValidationError, and each frame in Session.send, which raises BadRequestError for a frame the server would refuse (an unknown question id, an empty frame, an image by URL...) without writing anything or using a seq;
• for batches, the custom_id rules, an add without requests and batches.list paging.

decide_many and batches check every request first. After a models() call the client also checks the limits each model publishes there (a model that serves no sessions or answers no number questions, its maximum window, batch size and custom_id length), for a model named by its name, its alias or its pinned version. Limits counted in tokens stay the server's.

Check without sending

dn.check_request("decide", state=ticket, questions=questions, images=images)
dn.check_request("open_session", questions=questions, window=8)
dn.check_request("batches.create", requests=requests)
session.check_frame({"battery": 0.31}, questions=["abort"])

check_request(method, **arguments) runs every check the call method (decide, open_session, batches.create or batches.add) would run before sending, with the same arguments, and raises the same error; it sends nothing, uploads nothing and returns None when the request would go out. Session.check_frame(...) does the same for a frame. Neither makes a request, so neither is a coroutine on the async client.

A failed storage upload raises DecisionNodeError with error_type upload_failed, the storage's status, and its error code in reason. Storage PUTs are retried on 5xx and dropped connections like any call.

Only a 2xx is a success. Redirects are never followed, also on an http_client you pass in that is set to follow them: the client turns redirects off on every request it sends, so the key is never sent to another URL or over plain HTTP.

Your own HTTP client

http_client takes an httpx.Client (httpx.AsyncClient for the async client), for a proxy, custom certificates or connection limits. The client checks it when it is made and raises ValueError unless it can show that the key stays safe:

• It must be an httpx.Client (or httpx.AsyncClient) itself, not a subclass or another type: such a client could follow redirects whatever it is told.
• Its transports, including any in mounts, must be httpx's own HTTPTransport (AsyncHTTPTransport) or MockTransport. A transport of another type may follow redirects itself and is refused.
• For an https base URL, certificate and hostname checks must stay on: verify=False, or an ssl.SSLContext with check_hostname off or verify_mode other than CERT_REQUIRED, is refused. A custom CA (verify=ssl.create_default_context(cafile=...)) is fine.

import httpx

dn = DecisionNode(http_client=httpx.Client(proxy="http://proxy.example.com:3128"))

The client does not close an http_client you pass in.

Retries and timeouts

Each attempt times out after 10 seconds (30 for a request whose boosters name ocr, unless you set a timeout; see Boosters). The timeout covers the whole attempt, from sending the request to the last byte of the response body, so a server that answers slowly a little at a time cannot hold a call longer than that. A storage PUT of an image has its own deadline for the whole attempt, upload_timeout (60 seconds by default), since up to 10 MB may need longer than an answer does. Batch results are read from the network line by line as you iterate them, each read bounded by the timeout, so a file of any size is read whole. A failed request is retried twice on 408, 429, any 5xx (529 included), a timeout or a dropped connection; a request naming ocr is not retried after a timeout, since the server finishes that attempt. The wait is retry-after-ms when the server sends it, else Retry-After in seconds or as an HTTP date, capped at 60 seconds either way; without either, an exponential backoff from 0.5 seconds with jitter, capped at 8 seconds. A 408 still failing after its retries raises DecisionNodeError with status 408. 400, 401, 402, 403, 404 and 422 are never retried: the same request would fail again. Nor is a 429 key_spend_cap_reached: the key's cap resets at 00:00 UTC, so it is raised at once. A decision changes nothing on the server, so a retry is always safe.

dn = DecisionNode(timeout=5.0, max_retries=4)

Safety

On the hosted API every decision carries the result of the safety check:

d.safety  # Safety(checked=True, harm=0.031, self_harm=0.004, flagged=[], ...)

flagged lists the categories above your key's thresholds. When the check did not run, checked is false and reason says why. A self-hosted server sends nothing, and safety is None. A request the policy refuses raises RefusalError and is never retried.

The safety result in the body

The result always arrives in the x-decisionnode-safety response header. To also get it in the response body, send the request header x-decisionnode-safety-body: true. Pass it through headers, and it goes with every request of that client:

dn = DecisionNode(headers={"x-decisionnode-safety-body": "true"})

d = dn.decide(state="...", questions={"q": truth("Is this spam?")})
d.raw["safety"]  # {"checked": True, "harm": 0.031, "self_harm": 0.004, "flagged": []}

d.safety is the same with or without the header; the header only adds the field to d.raw.

Configuration

An argument wins over the environment, and the environment over the default. An empty string (api_key="", also model="" on a call) counts as not given. A client is safe to share between threads and tasks; close it with dn.close() (await dn.close()) or use it as a context manager.

Create one client and reuse it: it keeps its connections open between calls (up to 100, each kept for 30 seconds idle), so a call after the first needs no new connection or TLS handshake, and it remembers its image uploads.

The base URL must be https, so the key never travels unencrypted. Plain http is accepted only for localhost, 127.0.0.1 and ::1, for a server on the same machine; any other http URL, from the argument or the environment, raises ValueError when the client is made.

Raw requests

decide_raw(body) sends a request body exactly as given and returns the parsed response body, for an API field this version of the SDK does not know yet:

dn.decide_raw(
    {
        "model": "decisionnode-moe",
        "state": "",
        "questions": {"q": {"type": "truth", "instructions": "Is hotdog a sandwich?"}},
    }
)

Logging

The SDK sends no telemetry; the only identifying header it adds is User-Agent: decisionnode-python/<version>. It logs to the decisionnode logger at debug level, with the method, path, status, request id and timing of each attempt, never the state, questions, images or key (a storage URL is logged without its signature):

import logging

logging.getLogger("decisionnode").setLevel(logging.DEBUG)

Development

uv sync
uv run pytest

The tests include the DecisionNode SDK conformance suite (Bynn-Intelligence/decision-node-conformance), run with both the sync and the async client. Set DECISIONNODE_CONFORMANCE_DIR to a checkout of it, or check it out at conformance/ in this repository; without it the conformance tests fail rather than skip. The tests pass suite 1.20; CI checks the suite out at the commit pinned in CONFORMANCE_REF in .github/workflows/ci.yml, with every action pinned to a commit SHA and no checkout keeping its credentials.

DECISIONNODE_CONFORMANCE_DIR=/path/to/decision-node-conformance uv run pytest

This package implements version 1.2 of the specification shared by every official DecisionNode SDK, exported as decisionnode.SPEC_VERSION.

License

MIT. See LICENSE.