Explain SELECT Query

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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is known. The description adds the key behavior that it 'does not return row data,' which is important contextual information beyond the annotations. It also implies it expects a validated SELECT query, aligning with the safe, read-only nature. This adds value without contradicting annotations.

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?

The description is two sentences with zero filler. The core action and effect are front-loaded in the first sentence, and the usage guidance is in the second. No redundant information. It is perfectly sized for a simple read-only tool.

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 read-only diagnostic tool that has annotations covering safety and an output schema (which presumably documents the execution plan result), the description sufficiently conveys the purpose and usage. It doesn't explain error scenarios or the exact return format, but those are adequately covered by the output schema and annotations. It could mention that it works only on SELECT/SHOW/etc., but the schema already does that. Overall, it's complete enough for an agent to decide when to call it.

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% – all four parameters (sql, query, profile, magentoRoot) have descriptions in the schema. The tool description does not add any parameter-specific information beyond what the schema already provides. The phrase 'validated SELECT query' mirrors the schema's restriction on SQL prefix. With full schema coverage, the baseline of 3 applies, and the description adds negligible value about parameters.

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 clearly states the specific action ('Runs EXPLAIN'), the resource ('a validated SELECT query'), and the outcome ('shows the execution plan without returning row data'). This distinguishes it from siblings like execute_select_query and validate_select_query, even without naming them, because the verb 'EXPLAIN' and the explicit 'without returning row data' make the purpose unambiguous.

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 provides a clear usage context: 'Use to diagnose slow queries before running them on large Magento tables.' It implies this tool is for pre-execution diagnosis, not for actually running queries. However, it does not explicitly mention alternatives or when NOT to use this tool (e.g., when you need actual row data). Sibling tool names like execute_select_query hint at the distinction, but the description itself doesn't lay out exclusions.

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