SPDX - Software Package Data Exchange (format reference)

Companion reference for sbom-formats.md. Consult when the SBOM consumer requires SPDX (US Federal procurement, Linux Foundation members, license-compliance focus); the SKILL.md covers CycloneDX and the format-choice guidance.

SPDX is the Linux Foundation's SBOM standard, originally focused on license compliance. Per spdx.org/specifications:

Two active major versions:

When SPDX is the right format

• US Federal procurement context (NIST SP 800-218 + EO 14028 guidance favor SPDX).
• Linux Foundation member organization workflow.
• License-compliance focused use case (SPDX has the richest license-expression vocabulary).
• A consumer (regulator, customer) requires SPDX format specifically.

SPDX 2.3 top-level structure (JSON)

{
  "spdxVersion": "SPDX-2.3",
  "dataLicense": "CC0-1.0",
  "SPDXID": "SPDXRef-DOCUMENT",
  "name": "my-app-1.0.0-sbom",
  "documentNamespace": "https://example.com/spdx/my-app/1.0.0",
  "creationInfo": {
    "created": "2026-05-06T12:00:00Z",
    "creators": ["Tool: syft-1.16.0", "Organization: Acme Corp"]
  },
  "packages": [
    {
      "SPDXID": "SPDXRef-Package-myapp",
      "name": "my-app",
      "versionInfo": "1.0.0",
      "downloadLocation": "NOASSERTION",
      "filesAnalyzed": false,
      "licenseConcluded": "Apache-2.0",
      "licenseDeclared": "Apache-2.0"
    },
    {
      "SPDXID": "SPDXRef-Package-lodash",
      "name": "lodash",
      "versionInfo": "4.17.20",
      "downloadLocation": "https://registry.npmjs.org/lodash/-/lodash-4.17.20.tgz",
      "filesAnalyzed": false,
      "licenseConcluded": "MIT",
      "licenseDeclared": "MIT"
    }
  ],
  "relationships": [
    {
      "spdxElementId": "SPDXRef-DOCUMENT",
      "relationshipType": "DESCRIBES",
      "relatedSpdxElement": "SPDXRef-Package-myapp"
    },
    {
      "spdxElementId": "SPDXRef-Package-myapp",
      "relationshipType": "DEPENDS_ON",
      "relatedSpdxElement": "SPDXRef-Package-lodash"
    }
  ]
}

Required fields per SPDX 2.3

Per spdx-spec:

License expressions

SPDX is the canonical source for license identifiers (cross-format standard - even CycloneDX uses SPDX license IDs).

"licenseConcluded": "Apache-2.0",
"licenseConcluded": "MIT OR Apache-2.0",
"licenseConcluded": "(MIT AND BSD-3-Clause) OR GPL-2.0-only WITH Classpath-exception-2.0"

Full list: spdx.org/licenses (current count ~600+).

The LicenseRef- prefix declares custom licenses:

"hasExtractedLicensingInfos": [{
  "licenseId": "LicenseRef-AcmeProprietary",
  "extractedText": "Acme Proprietary License Text..."
}],
"licenseConcluded": "LicenseRef-AcmeProprietary"

Relationships

The relationships[] block is the dep-graph (SPDX equivalent of CycloneDX's dependencies[]):

Tag-Value format (SPDX-native)

Some toolchains use the SPDX Tag-Value format (older but well-tooled):

SPDXVersion: SPDX-2.3
DataLicense: CC0-1.0
SPDXID: SPDXRef-DOCUMENT
DocumentName: my-app-1.0.0-sbom
DocumentNamespace: https://example.com/spdx/my-app/1.0.0
Creator: Tool: syft-1.16.0
Creator: Organization: Acme Corp
Created: 2026-05-06T12:00:00Z

PackageName: my-app
SPDXID: SPDXRef-Package-myapp
PackageVersion: 1.0.0
PackageDownloadLocation: NOASSERTION
FilesAnalyzed: false
PackageLicenseConcluded: Apache-2.0
PackageLicenseDeclared: Apache-2.0

Relationship: SPDXRef-DOCUMENT DESCRIBES SPDXRef-Package-myapp

JSON is preferred for new toolchains; Tag-Value persists for legacy integrations.

SPDX 3.0 profiles and the SPDX tooling landscape are cataloged in spdx3-profiles-and-tooling.md; for most teams, stay on SPDX 2.3 unless 3.0 features are required.

Validation

# Python spdx-tools
pip install spdx-tools
pyspdxtools --infile sbom.spdx.json --version SPDX-2.3
# Validates structural conformance + license-expression syntax

# Validation via spdx online tool
# Upload to https://tools.spdx.org/app/

CI integration

jobs:
  spdx:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - uses: anchore/sbom-action@v0
        with:
          format: spdx-json
          output-file: sbom.spdx.json
      - run: |
          pip install spdx-tools
          pyspdxtools --infile sbom.spdx.json --version SPDX-2.3
      - uses: actions/upload-artifact@v4
        with:
          name: spdx-sbom
          path: sbom.spdx.json

Worked example

A team must deliver an SPDX 2.3 SBOM to a US Federal procurement consumer for an app that bundles one proprietary component:

1. Generates via Syft in CI: anchore/sbom-action with format: spdx-json, producing sbom.spdx.json with spdxVersion: "SPDX-2.3", dataLicense: "CC0-1.0", and a unique documentNamespace.
2. The app package uses a non-standard license, so the team declares it via hasExtractedLicensingInfos and sets licenseConcluded: "LicenseRef-AcmeProprietary"; every third-party package keeps its standard SPDX ID (MIT, etc.).
3. Adds relationships[]: SPDXRef-DOCUMENT DESCRIBES the app package, and the app DEPENDS_ON each dependency.
4. Validates: pyspdxtools --infile sbom.spdx.json --version SPDX-2.3 - structural + license-expression checks pass.

Result: a validated SPDX 2.3 JSON SBOM whose custom license resolves cleanly and whose relationship graph satisfies the federal consumer's format requirement.

SPDX anti-patterns

SPDX limitations

• SPDX 2.3 vuln support is weaker than CycloneDX 1.6 (no first-class vulnerabilities block - relies on companion VEX docs).
• License-expression validation is strict; non-standard licenses require LicenseRef- boilerplate.
• SPDX 3.0 tooling is still maturing; many tools still produce 2.3.
• Tag-Value parsing is whitespace-sensitive; subtle formatting bugs.

Sources

• spdx-spec - official specification
• spdx3-profiles-and-tooling.md - SPDX 3.0 profiles + tooling landscape
• spdx.dev - landing
• spdx.org/licenses - license ID list
• iso.org/standard/81870.html - ISO/IEC 5962:2021 (SPDX 2.2.1 ISO publication)
• tools.spdx.org - online validator
• github.com/spdx/tools-python - Python reference impl