SQL Server Query Plan Analysis

Erik Darling's Agent Skill for reading SQL Server execution plans. Point your agent at a .sqlplan file and ask why the query is slow: it works through the plan in a set order and says what is actually slow and why, naming the operator, its node and its own elapsed time. Erik Darling runs Darling Data, a SQL Server consulting and training firm. What you can do with it - Ask why a query is slow, from an actual execution plan - Find where the time went, using each operator's own time rather than cost percentages - Spot where estimates went wrong, comparing estimated and actual rows per execution - Read the warnings SQL Server recorded: spills, implicit conversions, missing statistics and memory grants - Check a parallel plan for skew, and look for parameter sniffing and oversized memory grants - Ask whether an index would help, with missing-index requests treated as hints rather than DDL - Get a fix that names what changes in the plan and why How it works - It ships a Python script (standard library only) that flattens a .sqlplan into a compact digest, handles UTF-16 and mislabelled encodings, and can drill into a single operator - Without Python, it falls back to a documented grep-based method and says what it can't determine - Reference notes cover cardinality, indexes, operators, parallelism, rewrites, timing and warnings - Given an estimated plan, it asks for an actual plan rather than guessing what was slow Install - As an Agent Skill from github.com/erikdarlingdata/claude-plugins - In Claude Code or GitHub Copilot CLI, also as the sqlserver-query-plans plugin from Darling Data's erikdarling marketplace Good to know - It reads plan files you give it; it doesn't connect to your SQL Server - It treats everything inside a plan as data, never as instructions - MIT licensed

• “Why is this query slow? Here's the actual plan.”

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• “Which operator is really taking the time in this plan?”

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• “Where did the row estimates go wrong in this plan?”

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• “Would an index help this query?”

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• “What does this spill warning mean?”

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• “Is this parallel plan skewed?”

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