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

Annotations already cover the safety profile (readOnlyHint, destructiveHint=false, idempotentHint), so the bar is lower, yet the description still adds non-obvious behavior: no credits are consumed and only the link's title and length are inspected, implying no download or transcription. It does not address whether the quote can drift if the video changes, but that is a minor omission against an otherwise well-disclosed read-only behavior.

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?

Two short clauses with zero filler: the estimate and the sufficiency check come first, and the read-only guarantee is stacked behind them as supporting reassurance. Nothing repeats the schema or the annotations verbatim.

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 six-parameter tool with no output schema, the description still tells the agent what comes back (a credit count and a yes/no on balance) and what inputs are consumed, which is the critical information. It leaves implicit that the other five parameters should be set to match the intended create_video call, so a small inference is still required.

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 description coverage is 100%, so all six parameters (including defaults for clips, captions, clip_length_seconds) are already documented in structured fields. The description only adds the framing that settings should mirror create_video's; it gives no extra meaning about how template or translate_to affect the price. Baseline 3 applies.

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?

Names a specific verb and object (estimates the credits create_video would spend on a link, plus whether the balance suffices) and explicitly ties itself to the sibling create_video. An agent can distinguish this from create_video or get_video 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?

"create_video would spend ... with the same settings" plus "spends nothing" makes the pre-flight-check use case clear, so an agent knows to call this before a paid generation. It stops short of an explicit "use this instead of create_video when you only need a price" or any stated exclusion, so it falls just short of the top band.

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