validate_vast

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

Beyond the readOnly/idempotent/destructive annotations, the description discloses meaningful behavior: auto-detection from the root element, the returned issue fields (severity, rule ID, location, spec reference), and the precise validity criterion (errors == 0 regardless of warnings). This is exactly the kind of behavioral detail an agent needs to interpret results correctly.

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

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

Four tight sentences front-load the purpose, then add supported versions, behavior, and validity semantics without any filler. Every sentence earns its place.

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

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

With an output schema present, the description doesn't need to enumerate return fields beyond what it already gives. It covers accepted formats, auto-detection, validity semantics, and wrapper-depth handling, making the tool fully callable without further investigation.

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

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

Schema coverage is 100%, so xml and wrapper_depth are already documented. The description adds value by explaining the wrapper_depth use case in wrapper chains and clarifying that document type is auto-detected, which helps the agent understand how the xml parameter will be interpreted.

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

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

The description names a specific verb ('Validate'), a precise resource ('IAB ad tag XML document'), and the supported formats (VAST 2.0-4.4, VMAP 1.0, DAAST). It also distinguishes this matrix-validation tool from the sibling validate_vast_url by focusing on an XML document rather than a URL.

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

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

The description gives clear guidance on when to use wrapper_depth ('when validating a VAST document inside a wrapper chain'), which is important operational context. It does not explicitly contrast with validate_vast_url or list exclusions, but the document-vs-URL distinction is implied by the resource and siblings.

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