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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered. The description adds a behavior not present in annotations: querying the balance does not itself consume credits, which is decision-relevant for an agent. It stops short of describing return format or any account scoping caveats.

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 short sentences, front-loaded with the purpose and followed by the one caveat that matters. No filler, no repetition of the title, no wasted tokens.

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?

For a no-param, read-only, closed-world tool with annotations covering the safety profile, the description says what is returned (remaining credit count) and that no credits are consumed. The only minor gap is that the response shape (e.g., a bare number vs. a message) is not hinted at, but the stakes are low.

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 input parameters, so the schema cannot be elaborated further and the baseline for an empty schema applies. Nothing in the description is needed or missing on this dimension.

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 gives a specific verb+resource: 'Show how many Shotlane render credits remain on this account.' The resource (account credit balance) is inherently distinct from the rendering-oriented siblings (html_to_pdf, read_page, screenshot), so an agent can route to it unambiguously.

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 by the purpose: call it when you need the remaining credit balance. It adds a useful reassurance ('Does not use credits') that lowers the cost of calling, but names no alternatives or when-not-to-use conditions, so guidance stays at the implied level.

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