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

With only readOnlyHint available in annotations, the description carries real extra weight: it explains that assist ops run on server-side small models rather than the caller's tokens, that the balance is debited by those ops, where credits originate (coupons or top-ups), and that exhaustion responses embed a top_up object with pay links. That is operational behavior an agent could not derive from the annotations or the empty schema.

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?

Three sentences, front-loaded with the purpose, then the mechanism (server-side models, balance debit), then the credits-source and exhaustion path. No filler, and every clause conveys something the agent acts on.

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 supplies the missing return-value information: the top_up object with pay links appears on zero balance or credits_exhausted. Combined with the annotation-declared read-only nature, an agent has everything needed to call and interpret this tool.

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; a baseline of 4 applies. The description correctly does not invent parameter guidance.

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+resource ('Check the user's XeoRank Assist credit balance') and names the exact concept — Assist credits — that separates it from siblings like assist_savings or get_usage. It also names the sibling operations that consume the balance (assist_classify_keywords), so the agent can place it in the workflow without opening any schema.

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 clear context for when the tool matters: when a balance is 0 or an assist op returns credits_exhausted, and it points to assist_redeem_coupon as the credit source. It stops short of an explicit 'call this before/after running an assist op' directive, so the invocation trigger is implied rather than stated.

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