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check_slot_children

Check that slot children match expected element types from the Custom Elements Manifest, catching invalid children like inside that requires .

Instructions

Validates that children placed inside a web component's slots match the expected element types from the CEM — catches wrong child elements in constrained slots (e.g. putting a inside which requires ). Parses slot descriptions for "Must be", "Works best with", and "Accepts" patterns.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
libraryIdNoOptional library ID to target a specific loaded library instead of the default.
htmlTextYesThe HTML code containing the component and its children to validate.
tagNameYesThe parent custom element tag name to check slot children for (e.g. "sl-select").
Behavior3/5

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

No annotations provided, so the description carries the full burden. It discloses it parses slot descriptions for specific patterns ('Must be', 'Works best with', 'Accepts') and gives an example, but does not cover edge cases, error handling, or performance implications.

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

Conciseness4/5

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

The description is concise with two sentences, front-loaded with the primary purpose. The first sentence is slightly lengthy but packs necessary details.

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

Completeness3/5

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

Given the complexity of slot validation and lack of output schema, the description is reasonably complete, mentioning pattern parsing and example. However, it does not explain return format or success/failure behavior.

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

Parameters3/5

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

Schema description coverage is 100%, so baseline is 3. The description does not add significant meaning beyond the schema; it reiterates the purpose of the parameters without providing format or syntax details.

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 the verb 'validates' and the resource 'children placed inside a web component's slots', with a concrete example. It distinguishes slot validation from sibling tools by focusing on slot children matching CEM types.

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

Usage Guidelines2/5

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

No explicit guidance on when to use this tool versus alternatives. The description implies usage for catching wrong child elements but does not mention when not to use or compare to similar tools like 'check_composition' or 'validate_usage'.

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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