Validating Content

• The Tiered Validation Model
• Validating FedRAMP Content with OSCAL CLI

The Tiered Validation Model

Validating OSCAL content is a tiered process that ensures data integrity from basic file structure to complex compliance requirements. For organizations following the Retrofit FedRAMP adoption path, validation requirements evolve as you move from initial MVP stages toward the full Target State.

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Layers of OSCAL Validation

To ensure high-quality authorization package data, OSCAL documents must pass through four distinct validation layers. Each layer builds upon the previous one, and a failure at any stage risks rendering the document invalid for FedRAMP submission.

Layer	Validation Type	Description
Well-Formed	File Format Valid	Confirms the XML, JSON, or YAML file follows the fundamental rules of its format. If a tool can parse the file without syntax errors, it is considered well-formed.
OSCAL Syntax	OSCAL Schema Valid	Verifies that the file uses only the names, structures, and values defined in the official NIST OSCAL schemas. This ensures the document aligns with the core model (e.g., SSP, SAP, or SAR).
Core OSCAL	Metaschema Valid	Uses Metaschema constraints to validate the internal data logic. This checks relationships within the document, ensuring that UUIDs match and cross-references between elements are functionally sound.
FedRAMP OSCAL	FedRAMP Valid	Enforces FedRAMP-specific business rules via an additional layer of constraints. This ensures the content meets technical requirements specific to the FedRAMP PMO, such as required metadata fields and specific parameter formatting.

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Validation and the Adoption Path

Validation is not a "one size fits all" requirement at the start of your transition. Depending on your current position in the Retrofit Adoption Path, your validation focus will shift:

• MVP Tier (Minimum Viable Product): Focus is primarily on Well-Formed and OSCAL Syntax validation. At this stage, the priority is successfully converting legacy data into an OSCAL-compliant structure.
• Intermediate Tier: Includes Core OSCAL validation. Relationships between components and controls must be logically sound as you begin to automate the mapping of your security architecture.
• Advanced Tier: Introduces FedRAMP validation. As the document matures, it must begin meeting the specific programmatic constraints required for official PMO review.
• Target State: Continuous validation across all four layers. In this state, you should automatically reject any changes that fail any validation layer, ensuring your "Source of Truth" remains submission-ready at all times.

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Recommended Tooling

Validation is most effective when integrated into the content development workflow rather than treated as a final check. The tools and resources listed below are highly recommended for OSCAL content validation.

• Metaschema OSCAL CLI: The Metaschema-Framework OSCAL-CLI is the primary tool for performing schema and Metaschema validation.
• FedRAMP Automation Suite (decommissioned): Specific validators created by the FedRAMP PMO to check against their unique business rules for Rev5 systems. This work is no longer maintained by FedRAMP but demonstrates how the OSCAL-CLI and external constraints can be used to validate OSCAL content against FedRAMP validation rules.
• IDE Extensions: Using integrated development environments (IDE) or similar editors with schema-aware extensions provides real-time feedback during the authoring process.
• AI-Assisted Remediation: Large Language Models (LLMs) and specialized AI agents can be used to automate validation of OSCAL documents, interpret complex validation error logs, and quickly generate corrected JSON/YAML snippets to remediate repetitive formatting issues.

Validating FedRAMP Content with OSCAL CLI

Get Started

The oscal-cli is an open source command-line utility designed to help developers and security professionals interact with OSCAL. To get started, follow the installation instructions from the OSCAL-CLI GitHub "README" page. Once installed, you can use the tool to perform core tasks such as validating OSCAL JSON, YAML, or XML files against the official schemas, converting between formats, and resolving "profile" documents into comprehensive "catalog" views. For those working in containerized environments, the tool is also available as a Docker image, allowing for easy integration into automated CI/CD compliance pipelines.

Commands

The following are a brief summary of the most commonly used oscal-cli commands when working with FedRAMP OSCAL documents.

Validate

Checks that the specified OSCAL file is well-formed and valid per OSCAL model and any additional specified constraints.

oscal-cli validate <file> -c <constraint-file> [options]

Convert

Converts an OSCAL source file to the specified file format (e.g., XML, JSON, or YAML).

oscal-cli convert --to=FORMAT <source-file-or-URL> <destination-file>

Profile Resolution

Creates a new tailored OSCAL catalog by combining baseline imported controls and applying any modifications, as specified in the source profile.

oscal-cli resolve-profile <profile-file>

Metaschema Validate

Validates that a Metaschema file is well-formed and valid per the specified constraint definitions.

oscal-cli metaschema validate <file> -c <style-guide> [options]

FedRAMP Validation Examples

Validating SSP Against FedRAMP Constraints

oscal-cli validate path/to/ssp.xml \
  -c path/to/fedramp-external-allowed-values.xml \
  -c path/to/fedramp-external-constraints.xml

Understanding Validation Errors

Common Error Messages

1. UUID Warning:

[WARNING] [.../protocol[1]] It is a best practice to provide a UUID.

Resolution: Add a unique UUID to the specified element.

2. Constraint Violations:

• Invalid allowed values
• Missing required fields
• Pattern matching failures

SARIF Output Integration

SARIF (Static Analysis Results Interchange Format) provides detailed validation results viewable in VS Code.

Generate SARIF Output

oscal-cli validate path/to/file.xml \
  -c path/to/constraints.xml \
  --sarif-include-pass \
  -o results.sarif.json

SARIF Features

• Detailed error locations
• Stack traces for debugging
• Pass/fail results for each rule
• VS Code integration for visual feedback

Best Practices

1. Always validate at both levels:
   • Basic OSCAL schema validation
   • FedRAMP constraints validation
2. Always validate against both allowed values and external constraints
3. Use SARIF output for detailed analysis:

   oscal-cli validate path/to/document.xml \
     -c path/to/constraints.xml \
     --sarif-include-pass \
     -o results.sarif.json
   

4. Address all warnings, even if they don't cause validation failures
5. Keep constraint files updated with latest FedRAMP requirements