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

Annotations already cover the read-only, non-destructive, closed-world profile. Beyond that, the description discloses the two billing models (credit-plan proration vs API per-second billing) and, importantly, the failure behavior: unstated length/resolution/audio/input yields a result without a price. That edge case is exactly the kind of context an agent cannot infer from the schema.

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 sentences, front-loaded with purpose, then the two pricing branches, then the edge case. Every sentence carries information, though the credit-plan sentence is dense and reads like a formula transcription rather than agent-directed guidance.

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 10-parameter read-only calculation tool with no output schema, the description covers the two computational paths and the no-price case, which is most of what an agent needs to interpret results. It stops short of describing the return shape, particularly the break-even note that window_seconds feeds, which is only alluded to in the 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 100%, so the schema already documents all 10 parameters well, and the baseline is 3. The description adds some semantic weight by naming which inputs (length, resolution, audio, input) can legitimately be missing and what that produces, but it does not clarify the plan-vs-provider interaction that the schema leaves slightly ambiguous.

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?

Opening sentence states a specific quantity (cost of one clip) and the source (the VidFare calculator), which tells an agent this is a compute-one-estimate tool rather than a price listing. It doesn't explicitly distinguish itself from siblings like get_model_prices or cheapest_options, which is the main thing keeping it from a 5.

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?

There is no when-to-use guidance and no naming of alternatives. The description explains the math behind the estimate but never says why an agent should call this instead of get_model_prices or cheapest_options, nor what prerequisites (plan vs provider) select which path.

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