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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds a genuinely new behavioral fact — the call is 'Free' — and discloses that params must be supplied per action, which the annotations do not convey.

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 and cost/balance outcome are front-loaded, followed by a compact parenthetical action→param map. It is dense but wastes no sentences; the single long action enumeration is the only mild readability cost.

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?

With no output schema, the description usefully signals the return semantics (credit cost plus whether the balance covers it). Combined with annotations covering safety and the schema covering the action enum and params, an agent has enough to call it correctly; only the exact response shape is unspecified.

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 the baseline is 3, but the description goes further by stating the required parameter combinations per action (clipper_analysis needs source_minutes; tts needs text or chars; studio needs model_key + model_params + count). That conditional requirement logic is absent from the schema, which only marks 'action' as required.

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 how many credits an action will cost') and adds the outcome dimension ('whether the current balance covers it'). An agent can immediately separate this pre-flight estimator from siblings like earnings_estimate or the actual generation tools such as generate_clips and studio_generate.

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?

The phrase 'before running it' establishes the trigger condition — call this prior to an expensive generation. The enumerated action list implicitly maps to the sibling tools that would otherwise be invoked (clips/generate_clips, tts/generate_voiceover, script/write_script, studio/studio_generate). It lacks an explicit 'do not use this to actually generate' exclusion, so it falls short of a 5.

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