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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: the reserved-vs-available distinction, the two pricing modes and their caps, and the fact that packs are only present when the endpoint sells credit. It omits auth needs, rate limits, and error behavior.

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?

It is a single dense sentence where every clause carries information, and it front-loads the balance figures before pricing and packs. The heavy nested parentheticals make it harder to parse than it needs to be, but there is little wasted text.

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 effectively serves as one, documenting balance, reserved, available, pricing modes, key id, and the packs array shape — a strong substitution. It is only slightly incomplete: the rate table structure is referenced but not described the way packs is.

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?

The schema has zero parameters, so there is nothing for the description to disambiguate — baseline 4 applies. All descriptive detail in the text is about return fields, not inputs.

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 enumerates exactly what the tool surfaces: balance_usd, reserved_usd/held_jobs, available_usd, pricing.mode, the rate table, the API key id, and packs. That specificity clearly separates it from the sibling job tools (submit_job, job_status, etc.), though it never states an explicit verb like 'Get' and opens with field names rather than a purpose statement.

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 only implied: the note that available_usd is 'what a new submit can use' hints you call this before submitting, and the pack top-up instruction is a how-to for a follow-up action, not a when-to-use rule. There is no explicit guidance on when to call this versus capabilities or preflight_deck.

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