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

Annotations already declare readOnly/idempotent/non-destructive, so the description correctly focuses on semantics beyond safety: the balance is the funding source for every generation started here, the limit is enforced by `generate`, and generations started in the Mage app also count against it. That last detail is non-obvious cross-surface behavior an agent could not infer from schema or annotations.

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 sentences: the first states what is returned, the second states why and when it matters. No filler, and the payload (the fields) is front-loaded before the rationale.

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 compensates by naming the three returned fields, and it adds the limit/error semantics needed to act on them. Nothing an agent needs to call and interpret this zero-arg read tool is missing.

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?

Zero parameters, so there is nothing to disambiguate and the baseline of 4 applies. The description appropriately spends no words on arguments and instead explains the returned values.

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?

Names a specific resource (the connected Mage account) and enumerates exactly what is returned: username, Gems balance, and in-flight generation count against the limit. This is clearly distinguishable from siblings like get_model or get_request, which target different resources.

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?

Explicitly says to read this 'before starting a batch' and names the sibling (generate) whose behavior depends on it, with the exact failure mode (`too_many_requests`) that motivates the pre-check. An agent has a concrete trigger for calling this tool and knows which alternative action it gates.

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