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

Annotations already declare this as a read-only, idempotent, non-destructive call, so the description doesn't need to re-litigate safety. It does add real context beyond the annotations: the 30-day cycle, that pool_resets_at is the next refill, the per-key daily cap, the tier origin of credits, and that the call is free.

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?

One dense sentence, front-loaded with the core answer (credits left) and followed by the supporting details. The parenthetical and the trailing 'Free.' are slightly telegraphic but nothing is wasted.

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 parameters and no output schema, the description carries the return-value burden, and it covers the main fields an agent needs (remaining credits, reset time, tier source, daily cap, zero cost). It stops short of stating format/units or whether caps are per-key vs per-account in a way an agent could act on without a sample response.

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?

There are zero parameters, so the baseline is 4. The description goes further by naming return fields (pool_resets_at, tier, daily cap), which is the only place that information exists given there is no output schema.

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 resource (remaining API credits) plus the extra data returned: reset timestamp, credit source/tier, and per-key daily cap. It's clear what the call yields, though it never explicitly contrasts itself with the sibling get_credit_packs, so differentiation is only implicit.

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 (check how many credits you have left before spending them), and 'Free' signals it costs nothing to call. There is no explicit when-to-use/when-not or pointer to get_credit_packs for topping up, so the agent must infer the boundary.

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