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explain_query

Read-only

Analyze SQL execution plans with cost estimates. Optionally run queries for real statistics or simulate hypothetical indexes to optimize performance.

Instructions

Explains the execution plan for a SQL query, showing how the database will execute it and provides detailed cost estimates.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
sqlYesSQL query to explain
analyzeNoWhen True, actually runs the query to show real execution statistics instead of estimates. Takes longer but provides more accurate information.
hypothetical_indexesNoA list of hypothetical indexes to simulate. Each index must be a dictionary with these keys: - 'table': The table name to add the index to (e.g., 'users') - 'columns': List of column names to include in the index (e.g., ['email'] or ['last_name', 'first_name']) - 'using': Optional index method (default: 'btree', other options include 'hash', 'gist', etc.) Examples: [ {"table": "users", "columns": ["email"], "using": "btree"}, {"table": "orders", "columns": ["user_id", "created_at"]} ] If there is no hypothetical index, you can pass an empty list.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior3/5

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

Annotations already indicate read-only behavior (readOnlyHint: true). The description adds that the tool shows how the database will execute and provides cost estimates, but it does not disclose any additional behavioral traits such as the impact of the 'analyze' parameter or potential performance implications.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, concise sentence that efficiently conveys the core functionality without unnecessary words. It is front-loaded with the action and resource.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

While the description covers the basic purpose, it does not mention optional parameters (analyze, hypothetical_indexes) or their effects. Given the output schema exists, return values are not needed, but the description could be more complete for a tool with three parameters and advanced features.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The description does not add meaning beyond the input schema, which already has 100% coverage with detailed parameter descriptions. Therefore, it meets the baseline of 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: explaining a SQL query's execution plan with cost estimates. It uses a specific verb ('explains') and resource ('execution plan'), and distinguishes it from sibling tools like execute_sql or analyze_query_indexes.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance on when to use this tool versus alternatives (e.g., when to use explain_query vs. analyze_query_indexes). The description lacks context about prerequisites or scenarios where it's appropriate.

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

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