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

Annotations cover readOnlyHint=true, so safety is already handled, but the description adds real behavioral traits beyond that: 'One immediate snapshot, never loop' (no polling) and the constraint that jp_ ids start a render elsewhere rather than being accepted here. It stops short of describing the snapshot's shape, hence a 4 rather than 5.

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?

Purpose is front-loaded, but the body is dense and repeats the routing idea in several phrasings ('NEVER answer null', 'pick by MEDIA WORD', the media-word list, the pair line). Useful content, but it reads as a routing memo rather than a tight definition and could be trimmed without losing coverage.

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?

For a single-param read-only status tool with no output schema, it covers trigger phrases, disambiguation, parameter origin, and the no-loop behavior. What the snapshot actually returns is left implicit, which is a minor gap given the absence of an output schema.

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 0% with a bare string param, so the description must carry the load — and it does: placeholder_id is the plain-UUID of an already-queued render originating from var2_join_videos or var2_render_timeline, and a jp_… id is explicitly rejected. That is substantive semantics absent from the schema.

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?

Opens with a specific verb+resource: 'Status check for a join / stitch render.' It explicitly carves itself apart from siblings by naming var2_get_video_result for plain video renders and var2_join_videos as its pair. An agent can route to it without opening a schema.

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?

Gives explicit when-to-use triggers ('is it ready / done yet', status question with an id/link), explicit when-not ('action verbs ... → the matching create/modify tool, NOT a status tool'), and named alternatives per media type. Exclusions and alternatives are both present.

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