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

Annotations already cover readOnlyHint, idempotentHint, and destructiveHint=false, so the description only needs incremental value. It supplies exactly that with 'Does not generate video or spend credits' — cost/billing information is not derivable from readOnlyHint (a read can still consume quota), and the up-front validation framing is useful. It does not, however, disclose that openWorldHint=true means external provider calls with their own latency/failure modes.

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 sentences, zero filler, with the differentiating constraint (no video, no credits) front-loaded in the second sentence. Nothing wastes space or buries the lede.

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?

There is no output schema, so the description carries the burden of explaining what comes back — yet it says nothing about the shape of list_input_modes, estimate_cost, or validate_request results, which is the primary reason an agent would call this. The input side is complete thanks to the 100%-covered schema, so this is adequate but has a clear return-value gap.

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%: identifier, functionName, and the nested params object are all documented with enums and per-function argument notes. The description adds nothing beyond the schema (no extra semantics for identifier/functionName/params), so the 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?

States a specific verb and resource ('Run a read-only Google Veo or xAI Grok video helper function') and explicitly delineates itself from the sibling generate_video by noting it 'Does not generate video or spend credits.' An agent can immediately tell this apart from generate_video and trigger_platform_helper.

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?

'before generation' gives a clear temporal/contextual trigger for when to call this tool, and the negation of generation implicitly routes the agent to generate_video for actual rendering. However, it never states when NOT to use it, nor does it recommend which of the three helper functions to prefer in a given situation (that is left to the schema).

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