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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered by structured data. The description adds nothing behavioral beyond that — no note about what is returned or any auth/rate context, though the output schema covers return values. Adequate but not additive.

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?

A single short sentence with no filler, and the invocation condition is front-loaded. It is well-sized for a one-parameter read tool, though it could have spent those few words stating the actual return instead of only the trigger.

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 annotations covering the safety profile and an output schema covering return values, most of the burden is lifted, so the description need not explain outputs. However, for a tool whose title and name hint at different concepts (credits vs. usage vs. plan), the description could have disambiguated what 'usage left' means; it remains minimal viable.

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 is a single required 'context' parameter whose purpose is fully documented in the schema (100% coverage), so the baseline of 3 applies. The description contributes no additional meaning about the parameter, which is acceptable here.

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 is phrased as a usage trigger ('when the user asks how much usage they have left or about their plan status') rather than stating what the tool does. Combined with the title 'Check usage' and name 'get_credits', an agent can infer it retrieves credit/plan usage data, but the description itself never says what it returns or that 'credits' equals usage/plan status. It is implied rather than stated.

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?

It gives a clear activation condition: user asks about remaining usage or plan status. That is concrete context for invoking it. It does not mention the adjacent 'upgrade_plan' sibling or any when-not condition, which keeps it 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.