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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds two pieces of genuine behavioral context beyond that: it actively refuses writes (rather than merely not writing) and it accepts only a single SELECT statement. However, it says nothing about what the explanation returns or whether it incurs query cost.

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 short sentences, the core action front-loaded, with the read-only constraint immediately after. No filler, and each clause adds a constraint the agent needs.

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 one-parameter tool with full schema coverage and rich annotations, the essentials are present. The main gap is that with no output schema, the description could clarify what an "explain" yields (plan tree, cost estimates, row counts), which matters for an agent deciding whether the output answers its question.

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 description coverage is 100% and there is a single required parameter whose schema text ("A single SELECT") matches the description's wording. The description adds no format, dialect, or length constraints beyond the schema, so 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?

The description states a specific verb ("Explain") and resource ("a single SELECT"), so an agent immediately understands this returns a query plan rather than results. It implicitly contrasts with the sibling sql.execute but never names it, so sibling differentiation is left to inference.

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 for inspecting a query plan before running it. There is no explicit when-to-use statement, no mention of sql.execute as the alternative for actually running the statement, and no guidance on when explaining is preferable to executing.

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