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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the description only needs to add context — and it does: it names the exact return shape, states a per-call price (2 credits, 1 credit = 1 CAD cent, charged on success only), and says malformed input is rejected before billing. The only gap is that it never states the query is not executed (that fact lives only in the schema) and leaves 'performance and safety risks' undefined.

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, purpose front-loaded, then the return shape and the billing caveat. Every clause carries information an agent needs (output keys, cost, rejection behavior) with no filler.

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?

No output schema exists, and the description compensates by enumerating the four return fields. Combined with pricing and input-rejection behavior, an agent has everything needed to decide to call it and how to read the result.

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% and there is a single required `sql` parameter whose description already covers length limits and non-execution. The description adds no parameter-level detail beyond what the schema provides, 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?

States a specific verb and resource ('Explains a SQL query step by step') plus the distinctive value it adds: risk flags and index suggestions. No sibling in the list touches SQL, so there is no ambiguity about which tool to pick.

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 makes the use case clear (analyze a single SQL statement for structure, performance, and safety) and the constraint that input must match the schema. It does not articulate when to prefer a different approach, but the sibling set contains no alternative SQL-analysis tool, so exclusions are unnecessary.

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