ocsf-semtools

ocsf-semtools brings the complete rules of OCSF to Python, for every OCSF release since 1.0.0. The library builds an event from the fields a producer knows and fills in what the schema defines: class and category IDs, type_uid, and the label beside every enum. It checks events from any source against the same rules and returns every problem in one report, each with a path and a severity. It also extracts observables, shows what changed between two OCSF versions, and generates typed msgspec models from the same schema.

Status: alpha. Minor releases before 1.0 may change the API, and the changelog lists every change.

Install

pip install --pre ocsf-semtools          # core: every OCSF release since 1.0.0, as data
pip install --pre ocsf-semtools-v1-9-0   # optional: typed models for one OCSF version

Typed models lists the packages available.

ocsf-semtools generate builds a model package for any other version or extension set (see Command line).

Python 3.12 or newer. The only runtime dependency is msgspec.

Build and emit one event

Pick an OCSF version and a class, give the fields you know, and build fills in what the schema derives: class and category identity, type_uid, the label beside every _id enum, and metadata.version.

>>> import json
>>> from ocsf_semtools import build, load
>>> schema = load("1.9.0")
>>> event = build(
...     (schema, "detection_finding"),
...     activity_id=1,
...     severity_id=4,
...     time=1_700_000_000_000,
...     metadata={"product": {"name": "Sensor", "vendor_name": "Acme"}},
...     finding_info={"uid": "f-1", "title": "Suspicious login"},
... )
>>> print(json.dumps(event, indent=2, sort_keys=True))
{
  "activity_id": 1,
  "activity_name": "Create",
  "category_name": "Findings",
  "category_uid": 2,
  "class_name": "Detection Finding",
  "class_uid": 2004,
  "finding_info": {
    "title": "Suspicious login",
    "uid": "f-1"
  },
  "metadata": {
    "product": {
      "name": "Sensor",
      "vendor_name": "Acme"
    },
    "version": "1.9.0"
  },
  "severity": "High",
  "severity_id": 4,
  "time": 1700000000000,
  "type_name": "Detection Finding: Create",
  "type_uid": 200401
}

build raises ConformanceError if the event can't conform, and the error carries every problem it found:

>>> from ocsf_semtools import ConformanceError
>>> try:
...     build((schema, "detection_finding"), severity_id=4, time=1)
... except ConformanceError as error:
...     for finding in error.report.errors():
...         print(finding.message)
activity_id is required and absent
finding_info is required and absent
metadata is required and absent

Check an event you received

parse returns the event with a report of findings, each with a kind, an indexed path and a severity. The caller decides which findings are fatal.

>>> from ocsf_semtools import parse
>>> received = dict(event, severity_id=9, status_id="x")
>>> _, report = parse(received)
>>> report.ok()
False
>>> for finding in report.errors():
...     print(finding.kind.value, finding.path, finding.message)
enum_out_of_range ('severity_id',) severity_id is not one of [0, 1, 2, 3, 4, 5, 6, 99]
type_mismatch ('status_id',) status_id is a str; expected integer_t

The version and profiles come from the event's own metadata. repair returns a normalized copy and records every change it made. The same check runs from the shell over JSON Lines files: ocsf-semtools check --version 1.9.0 events.jsonl.

Typed models

With ocsf-semtools-v1-9-0 installed, every class and object is a msgspec Struct, every enum is referenceable by its caption, and build and parse accept and return the typed classes:

import msgspec

from ocsf_semtools import build, parse
from ocsf_semtools_v1_9_0 import DetectionFinding
from ocsf_semtools_v1_9_0.classes.detection_finding import DetectionFindingActivityId
from ocsf_semtools_v1_9_0.enums import SeverityId
from ocsf_semtools_v1_9_0.objects import FindingInfo, Metadata, Product

finding = build(
    DetectionFinding,
    activity_id=DetectionFindingActivityId.CREATE,
    severity_id=SeverityId.HIGH,
    time=1_700_000_000_000,
    metadata=Metadata(product=Product(name="Sensor", vendor_name="Acme")),
    finding_info=FindingInfo(uid="f-1", title="Suspicious login"),
)
assert finding.type_uid == 200401
wire = msgspec.json.encode(finding)  # the event as JSON bytes

same, report = parse(msgspec.json.decode(wire), as_=DetectionFinding)
assert same == finding and report.ok()

The models type-check under strict pyright, and importing one class loads only that class's module.

More

• Schema as data: required attributes, enums and captions, siblings, profiles, class identity, all without building an event.
• Building and checking events: build, parse, repair, what each one changes, and reports.
• Observables: extracting and merging the observables an event carries.
• Schema diff: what changed between two OCSF versions, renames included.
• Typed models: the model packages, and generating your own (custom extensions and exact profile sets).
• Command line: check, diff, generate and the schema pipeline.

How versions work

Each OCSF release is compiled with the official ocsf-schema-compiler from an exact upstream commit, recorded in ocsf.lock. CI recompiles every release and confirms that the shipped schema still matches the upstream compiler's output. The core package carries every release, so events of any version can be checked, repaired, diffed and mined for observables. Typed models come as one package per release for the newest three, so a project installs only the versions it produces.

The library follows SemVer on its own API, and before 1.0 a minor release may change it. Support for a new OCSF release arrives in a minor release. A model package accepts every core release up to the next minor, so core bugfixes install under it unchanged.

Other OCSF libraries

Several Python packages cover parts of OCSF. pydantic-ocsf offers Pydantic models across OCSF versions, and its computed type_uid and sibling-label checks shaped ideas here. py-ocsf-models provides models for finding classes. ocsf-lib provides schema tooling for compiling, diffing and compatibility checks. The Go library ocsf/ocsf-toolkit enriches and validates events against a compiled schema.

The table compares major features as of 2026-11-08, one release per column.

● full · ◕ mostly · ◑ partial · ◔ minimal · ○ none · ? not tested

License

Apache-2.0. The bundled schema data is compiled from the OCSF schema, © OCSF a Series of LF Projects, LLC, also under Apache-2.0; NOTICE carries its notice. ocsf-semtools is an independent project with no affiliation to OCSF, and is separate from the Go library ocsf/ocsf-toolkit.