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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so 'Read-only' restates structured data. The genuinely additive part is the failure contract — plan is null with a reason if the balance check fails — which tells the agent how to detect a failed fetch rather than hallucinate a balance. It does not cover auth, latency, or staleness.

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 compact sentences with the read-only contract front-loaded, then the return semantics, then the parameter modifier and the failure caveat. The density is justified, though the resolution/premium enumeration is slightly crammed into one clause.

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 must convey return shape, and it does: seconds at three quality tiers, optional per-series episode seconds, and a null plan with a reason on failure. Only minor gaps remain, such as what premium means quantitatively or which series quality applies by default.

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 0% for the single series_id parameter, so the description has to carry it, and it does explain the effect (adds 30-second episodes left at that series' quality). It stops short of saying what format an ID takes or where to obtain it, leaving a gap for a 0%-coverage parameter.

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?

The description names a specific resource (real credit balance from agent-media) and states exactly what that balance is expressed as: seconds left at 480p, 720p and premium, plus per-series episode seconds when series_id is supplied. That distinguishes it from planning siblings like get_season_plan, though it never names an alternative explicitly.

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?

Usage is implied rather than stated: the 'never guess' instruction signals this tool is the authoritative source for balance instead of estimating, and the series_id clause hints at when to pass the parameter. There is no explicit when-to-use/when-not-to-use against get_season_plan or get_series_costs.

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