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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description adds real domain context beyond them: which operations consume credits (images, video, transcription, scraping) and which are free on paid plans, which lets an agent interpret the returned number rather than just read it.

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, front-loaded with the return value, and the second sentence earns its place by explaining what the balance actually pays for. No filler or restatement of the title.

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 must carry the return contract, and it only says "the credit balance" without indicating the shape (single number, remaining vs. plan allotment). It also never routes the agent to buy_credits when the balance is insufficient, a clear gap for a zero-parameter utility in a 70+ sibling toolset.

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 tool takes zero parameters, so there is nothing for the description to disambiguate; the empty schema is fully self-explanatory. Baseline of 4 applies.

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 verb and resource ("Returns the credit balance for the workspace") and scopes it to the workspace, which separates it from user-level lookups like get_user. It does not explicitly contrast with buy_credits or the estimate_*_cost siblings, so the differentiation is implicit 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?

Usage is only implied: an agent can infer this is the pre-flight check before generate_image/generate_video or a top-up via buy_credits, but the description never says so. There are no when-to-use or when-not-to-use statements and no named alternative.

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