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by awslabs

get_child_element

Retrieve a single child element by its identifier (UUID or token ID) from OSCAL documents, with optional parent document UUID to resolve ambiguous IDs across multiple documents.

Instructions

Retrieve a single child element by its identifier.

OSCAL uses two identifier schemes:

  • UUIDs (globally unique) for most elements such as tasks, activities, results, findings, POA&M items, mappings, and system-components.

  • Token IDs (e.g. ac-1, sc) for catalog controls and groups — these are human-readable but only unique within their containing document.

For elements with token-based IDs, parent_doc_uuid should be provided to disambiguate. For elements with UUIDs, parent_doc_uuid is optional.

If parent_doc_uuid is omitted and the element_id matches elements in more than one document, an error dict is returned with error: "ambiguous_element_id" and a list of matching parent document UUIDs so the caller can retry with disambiguation.

Args: ctx: MCP server context (injected automatically). element_id: The element identifier (UUID or token ID). parent_doc_uuid: Optional parent document UUID to scope the lookup using the composite key (element_id, parent_doc_uuid).

Returns: A dict with keys: id, title, element_type, description, parentDocumentTitle, parentDocumentUuid, raw_json — or None if not found. Returns an error dict if the element_id is ambiguous across documents.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
element_idNo
parent_doc_uuidNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations provided, but the description fully discloses behavior: it returns a dict or None, details the error response for ambiguous IDs, and explains the composite key lookup. The read-only nature is implied by 'retrieve'.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Well-structured: starts with core purpose, explains identifier schemes, then parameter usage, error case, and ends with formal Args/Returns. Every sentence adds value, no redundancy.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool has an output schema, the description still covers return format and error handling. It thoroughly explains parameter behavior and identifier types, making it fully self-contained for an agent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0%, but the description provides detailed semantics for both parameters: element_id (UUID or token ID) and parent_doc_uuid (optional, for disambiguation with examples). This adds significant meaning beyond type/default alone.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'Retrieve a single child element by its identifier,' specifying the verb and resource. It distinguishes from sibling list/query tools by focusing on a single element and includes details about identifier types.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly explains when to use the optional parent_doc_uuid (for token-based IDs to disambiguate) and notes the error case for ambiguous IDs. It implicitly differentiates from list tools.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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