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

Annotations already declare readOnly/idempotent/non-destructive and open-world, so safety is covered. The description adds genuinely new behavioral context beyond the structured fields: the Pro-tier paywall and the requirement to bring a personal Solscan API key, which materially affects whether a call will succeed.

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 short clauses with zero padding: what it returns, the field list, then the access constraint. Purpose is front-loaded and the caveat is placed after the core value, which is the right order.

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?

An output schema exists, so the brief return-field mention is a convenience rather than a duty, and pagination is fully specified in the schema. The one gap is that the Pro-tier restriction is raised without naming a Free-tier substitute, which is the remaining thing an agent would need.

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?

Schema coverage is 100% — address, page (1-based, default 1) and page_size (1-40, default 20) are all documented in the schema with defaults. The description adds nothing about parameter semantics, so the baseline 3 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?

"SPL-token balances held by a Solana account" names a specific resource and scope, and the enumerated return fields (mint, symbol, amount, decimals, USD value) confirm exactly what kind of data comes back. It is not tautological and reads distinctly from neighbors like get_token_meta or get_account_detail, though it never names a sibling to sharpen the boundary.

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?

The description states a hard eligibility gate — Pro tier, caller must supply their own Solscan API key because the platform key is Free tier — which tells the agent when this tool is callable at all. It gives no when-to-use-vs-alternative guidance, so an agent hitting the tier wall is left to guess which sibling to fall back on.

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