performance-check

performance-check is a skill for Claude Code, Codex from joris887/exosuit. It costs 36 tokens per session (850 once invoked), scanned A, original, MIT.

A read-only review of code for runtime speed, memory use, database access, input/output, and behavior under increasing load. It looks for patterns such as repeated database queries inside loops and operations that grow without a bound.

In plain words
What is it for?
Use it to inspect changed performance-sensitive code, check for N+1 database queries, blocking input/output, memory leaks, inefficient algorithms, and missing caching opportunities.
Why use it?
It can reveal slow paths, excessive resource use, and scaling problems before they become production issues. It focuses on analysis and does not edit the code.

Skill for Claude CodeCodex

Part of the exosuit plugin — 44 skills, 1 command, 9 agents, 10 hooks shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/joris887/exosuit/performance-check
Any agent
npx skills add joris887/exosuit --skill performance-check
Clone the repo
git clone --depth 1 https://github.com/joris887/exosuit

Made for: Claude Code, Codex.

Or install exosuit, the plugin that ships this one along with the rest of its 44 skills, 1 command, 9 agents, 10 hooks.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for performance-check

README.md
[![agentmods](https://agentmods.dev/badge/skills/joris887/exosuit/performance-check.svg)](https://agentmods.dev/skills/joris887/exosuit/performance-check)
Your own site
<a href="https://agentmods.dev/skills/joris887/exosuit/performance-check"><img src="https://agentmods.dev/badge/skills/joris887/exosuit/performance-check.svg" alt="Measured on agentmods" height="20"></a>
Per session 36 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 850 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00036 $0.00850
Opus 5 $0.00018 $0.00425
Sonnet 5 $0.00007 $0.00170
Haiku 4.5 $0.00004 $0.00085

Measured 4d ago against content hash 6b64e5cded11, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

performance-check scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/performance-check/SKILL.md · 107 lines

How it starts

The opening of the file, as written. The whole thing — 107 lines — stays where its author put it; the contents beside it link to each section on GitHub.


performance-check

Check for N+1 queries in database access code Analyze performance patterns in changed files Review scaling behavior of the API layer

You are a performance engineer analyzing code for runtime efficiency and scaling behavior.

Tool restriction: This agent MUST only use Read, Glob, Grep, and Bash (for running profiling/benchmarking tools). Do NOT use Edit or Write. This is a read-only analysis agent.

Mindset: Think about what happens at 10x, 100x, and 1000x the expected load. Focus on the hot paths — the 20% of code that handles 80% of the load.

Analysis Process

  1. Identify hot paths — What code runs on every request or handles the most data?
  2. Database query analysis — Find queries inside loops (N+1), missing indexes, SELECT *
  3. I/O analysis — Synchronous operations that could be async, missing connection pooling
  4. Memory analysis — Growing collections, unclosed resources, retained references
  5. Scaling analysis — What's the algorithmic complexity? Does it scale linearly or worse?
  6. Caching opportunities — Stable data fetched repeatedly, missing cache layers

Checks to Perform

N+1 Query Detection

Search for database calls inside loops:

# Common patterns across languages
grep -rn "for.*\(.*SELECT\|\.find(\|\.get(\|\.query(" --include='*.py' --include='*.ts' --include='*.js' --include='*.go' --include='*.rb' . 2>/dev/null

Unbounded Operations

  • Missing LIMIT on database queries
  • Missing pagination on API endpoints
  • Loops without upper bounds
  • Promise.all() or goroutine launch without concurrency limits

Blocking I/O in Async Contexts

  • Synchronous file reads in request handlers
  • Blocking HTTP calls in async functions
  • Missing connection pooling

Memory Patterns

  • Collections that grow without bounds (append-only arrays, growing maps)
  • Event listeners not removed
  • Large objects in closures

Read the full file on GitHub · 107 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 107 lines · 36 tokens per session scan A 6b64e5cded11

Subscribe to this mod's changes

performance-check is a skill published in the GitHub repository joris887/exosuit (4 stars, last pushed 15d ago), licensed MIT. It adds 36 tokens to every session and 850 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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