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explain_query

Read-onlyIdempotent

Analyze a SQL query's execution plan and return plain-English performance recommendations. What runs, per dialect: postgres — EXPLAIN (FORMAT JSON), an ESTIMATED plan; the query is NOT executed and there are no measured timings (ANALYZE would execute it). mysql 8.0.18+ — EXPLAIN ANALYZE, which DOES execute the query to obtain real timings. mysql <8.0.18 — EXPLAIN FORMAT=JSON (estimated). mssql — SET SHOWPLAN_XML ON (estimated, not executed). Costs and row counts on an estimated plan are the planner's guesses: report them as estimates, not as observed behaviour. [BUILD tier]

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
sqlYesThe SELECT query to analyze
connectionNoTarget connection name from this tenant's inventory. Call `list_connections` to see every name + dialect, then match semantically to the user's intent (e.g. 'analytics' → a connection named `*-analytics-*`; 'prod' → a connection with `prod-` prefix). If the user didn't specify, use the tenant's default (first added). Do not invent names — resolve from `list_connections` output.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
dataNo
metaNo
displayNo
summaryNo
insightsNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedOutput schema / properties / data / anyOf
      Previous value: -[
      -  {
      -    "additionalProperties": true,
      -    "properties": {
      -      "original_sql": {
      -        "type": "string"
      -      },
      -      "plan": {}
      -    },
      -    "type": "object"
      -  },
      -  {
      -    "additionalProperties": true,
      -    "properties": {
      -      "code": {
      -        "type": "string"
      -      },
      -      "details": {
      -        "additionalProperties": {},
      -        "type": "object"
      -      },
      -      "error": {
      -        "type": "string"
      -      },
      -      "internal_code": {
      -        "type": "string"
      -      },
      -      "message": {
      -        "type": "string"
      -      },
      -      "retry_after_s": {
      -        "type": "number"
      -      }
      -    },
      -    "type": "object"
      -  }
      -]New value: +[
      +  {
      +    "additionalProperties": true,
      +    "properties": {
      +      "original_sql": {
      +        "type": "string"
      +      },
      +      "plan": {}
      +    },
      +    "type": "object"
      +  },
      +  {
      +    "additionalProperties": true,
      +    "properties": {
      +      "code": {
      +        "type": "string"
      +      },
      +      "details": {
      +        "additionalProperties": {},
      +        "type": "object"
      +      },
      +      "error": {
      +        "type": "string"
      +      },
      +      "internal_code": {
      +        "type": "string"
      +      },
      +      "message": {
      +        "type": "string"
      +      },
      +      "retry_after_s": {
      +        "type": "number"
      +      }
      +    },
      +    "required": [
      +      "error"
      +    ],
      +    "type": "object"
      +  }
      +]
  2. Changed2 schema fields changed
    • addedInput schema / properties / connection / maxLength
      Added value: +256
    • addedInput schema / properties / sql / maxLength
      Added value: +50000
  3. Changed2 schema fields changed
    • addedOutput schema / properties / display / properties / map
      Added value: +{
      +  "additionalProperties": true,
      +  "properties": {
      +    "label": {
      +      "type": "string"
      +    },
      +    "lat": {
      +      "type": "string"
      +    },
      +    "lon": {
      +      "type": "string"
      +    },
      +    "title": {
      +      "type": "string"
      +    }
      +  },
      +  "type": "object"
      +}
    • changedOutput schema / properties / display / properties / type / anyOf
      Previous value: -[
      -  {
      -    "enum": [
      -      "table",
      -      "chart",
      -      "metric",
      -      "code",
      -      "text",
      -      "list"
      -    ],
      -    "type": "string"
      -  },
      -  {
      -    "type": "string"
      -  }
      -]New value: +[
      +  {
      +    "enum": [
      +      "table",
      +      "chart",
      +      "metric",
      +      "code",
      +      "text",
      +      "list",
      +      "map"
      +    ],
      +    "type": "string"
      +  },
      +  {
      +    "type": "string"
      +  }
      +]
  4. Changed1 schema field changed
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
      +  "$schema": "http://json-schema.org/draft-07/schema#",
      +  "additionalProperties": true,
      +  "properties": {
      +    "data": {
      +      "anyOf": [
      +        {
      +          "additionalProperties": true,
      +          "properties": {
      +            "original_sql": {
      +              "type": "string"
      +            },
      +            "plan": {}
      +          },
      +          "type": "object"
      +        },
      +        {
      +          "additionalProperties": true,
      +          "properties": {
      +            "code": {
      +              "type": "string"
      +            },
      +            "details": {
      +              "additionalProperties": {},
      +              "type": "object"
      +            },
      +            "error": {
      +              "type": "string"
      +            },
      +            "internal_code": {
      +              "type": "string"
      +            },
      +            "message": {
      +              "type": "string"
      +            },
      +            "retry_after_s": {
      +              "type": "number"
      +            }
      +          },
      +          "type": "object"
      +        }
      +      ]
      +    },
      +    "display": {
      +      "additionalProperties": true,
      +      "properties": {
      +        "chart": {
      +          "additionalProperties": true,
      +          "properties": {
      +            "chartType": {
      +              "type": "string"
      +            },
      +            "color": {
      +              "type": "string"
      +            },
      +            "title": {
      +              "type": "string"
      +            },
      +            "x": {
      +              "type": "string"
      +            },
      +            "xLabel": {
      +              "type": "string"
      +            },
      +            "y": {
      +              "anyOf": [
      +                {
      +                  "type": "string"
      +                },
      +                {
      +                  "items": {
      +                    "type": "string"
      +                  },
      +                  "type": "array"
      +                }
      +              ]
      +            },
      +            "yLabel": {
      +              "type": "string"
      +            }
      +          },
      +          "type": "object"
      +        },
      +        "code": {
      +          "additionalProperties": true,
      +          "properties": {
      +            "executable": {
      +              "type": "boolean"
      +            },
      +            "language": {
      +              "anyOf": [
      +                {
      +                  "enum": [
      +                    "sql",
      +                    "json",
      +                    "bash",
      +                    "typescript"
      +                  ],
      +                  "type": "string"
      +                },
      +                {
      +                  "type": "string"
      +                }
      +              ]
      +            },
      +            "title": {
      +              "type": "string"
      +            }
      +          },
      +          "type": "object"
      +        },
      +        "metric": {
      +          "additionalProperties": true,
      +          "properties": {
      +            "label": {
      +              "type": "string"
      +            },
      +            "status": {
      +              "anyOf": [
      +                {
      +                  "enum": [
      +                    "good",
      +                    "warning",
      +                    "critical"
      +                  ],
      +                  "type": "string"
      +                },
      +                {
      +                  "type": "string"
      +                }
      +              ]
      +            },
      +            "trend": {
      +              "anyOf": [
      +                {
      +                  "enum": [
      +                    "up",
      +                    "down",
      +                    "neutral"
      +                  ],
      +                  "type": "string"
      +                },
      +                {
      +                  "type": "string"
      +                }
      +              ]
      +            },
      +            "trendValue": {
      +              "type": "string"
      +            },
      +            "unit": {
      +              "type": "string"
      +            },
      +            "value": {
      +              "type": [
      +                "string",
      +                "number"
      +              ]
      +            }
      +          },
      +          "type": "object"
      +        },
      +        "type": {
      +          "anyOf": [
      +            {
      +              "enum": [
      +                "table",
      +                "chart",
      +                "metric",
      +                "code",
      +                "text",
      +                "list"
      +              ],
      +              "type": "string"
      +            },
      +            {
      +              "type": "string"
      +            }
      +          ]
      +        }
      +      },
      +      "type": "object"
      +    },
      +    "insights": {
      +      "items": {
      +        "additionalProperties": true,
      +        "properties": {
      +          "column": {
      +            "type": "string"
      +          },
      +          "message": {
      +            "type": "string"
      +          },
      +          "severity": {
      +            "anyOf": [
      +              {
      +                "enum": [
      +                  "info",
      +                  "warning",
      +                  "critical"
      +                ],
      +                "type": "string"
      +              },
      +              {
      +                "type": "string"
      +              }
      +            ]
      +          },
      +          "value": {}
      +        },
      +        "required": [
      +          "severity",
      +          "message"
      +        ],
      +        "type": "object"
      +      },
      +      "type": "array"
      +    },
      +    "meta": {
      +      "additionalProperties": true,
      +      "properties": {
      +        "cacheHit": {
      +          "type": "boolean"
      +        },
      +        "connection": {
      +          "type": "string"
      +        },
      +        "dialect": {
      +          "anyOf": [
      +            {
      +              "enum": [
      +                "postgres",
      +                "mysql",
      +                "mssql"
      +              ],
      +              "type": "string"
      +            },
      +            {
      +              "type": "string"
      +            }
      +          ]
      +        },
      +        "executionTimeMs": {
      +          "type": [
      +            "number",
      +            "string"
      +          ]
      +        },
      +        "plan": {},
      +        "rowCount": {
      +          "$ref": "#/properties/meta/properties/executionTimeMs"
      +        },
      +        "tool": {
      +          "type": "string"
      +        },
      +        "truncated": {
      +          "type": "boolean"
      +        }
      +      },
      +      "type": "object"
      +    },
      +    "summary": {
      +      "type": "string"
      +    }
      +  },
      +  "type": "object"
      +}
  5. First observed

TDQS

A4.2/5.0
Behavior5/5

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

Despite readOnlyHint=true, the description transparently discloses that mysql 8.0.18+ executes the query via EXPLAIN ANALYZE, while other dialects do not. It also warns that costs/row counts are estimates on estimated plans, adding critical behavioral nuance beyond annotations. No contradiction with annotations.

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

Conciseness4/5

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

The description is dense but well-organized by dialect, front-loading the primary purpose. Each sentence provides distinct value—no filler. It is longer than average but justified by the dialect matrix and estimate caveat.

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

Completeness5/5

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

Given the tool's complexity (dialect variations, execution vs estimated) and that an output schema exists, the description covers all necessary operational aspects: what runs per dialect, whether the query executes, and how to interpret results. No critical behavioral gaps remain.

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?

Schema description coverage is 100%, with both 'sql' and 'connection' parameters already described in the input schema. The tool description adds no new parameter-level detail, so baseline 3 applies. It does not clarify parameter semantics beyond the schema.

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 opens with a clear verb+resource: 'Analyze a SQL query's execution plan and return plain-English performance recommendations.' This is specific and distinguishes it from siblings like query_sql or optimize_query by focusing on execution plan analysis with human-readable output.

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

Usage Guidelines3/5

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

The description explains dialect-specific execution behavior but does not provide explicit when-to-use vs alternatives guidance. It implies usage for performance analysis but never names a sibling like optimize_query or find_n_plus_one, nor states when not to use it. The context of siblings is left to the agent to infer.

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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