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

Consistent with readOnlyHint=true and destructiveHint=false: it estimates against cost tables and spends nothing. Beyond the annotations it discloses the user-approval gate that must precede a render and that render_ad needs no confirmation, which is real procedural context. It does not say what the returned quote contains or how firm the estimate is.

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?

Three short sentences, front-loaded with the purpose, then the alternative, then the approval requirement. No filler and no repetition of the schema.

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?

The safety and routing picture is complete for a single-parameter, read-only estimator. The only gap is that, with no output schema, the description never indicates what the estimate returns (credits? per-scene cost? a breakdown), so the agent knows when to call it but not what to expect back.

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?

Only one parameter, scenes, and the schema already describes it fully ("typically 3-5"), so the description carries little parameter burden. The description adds nothing about how scene count affects the estimate, which is the baseline 3 expected at 100% schema coverage.

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 ("Estimate an ad plan") plus the mechanism (the render engine's cost tables), and explicitly distinguishes itself from render_ad by contrasting this estimate with "a saved ad's exact remaining cost." An agent can route between the two without opening either 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 the when (before anything is spent), the when-not with the named alternative (use render_ad with adId and no confirmation for a saved ad's exact remaining cost), and the prerequisite that a render requires the user to approve the quote. That is explicit routing plus the gating condition.

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