online-algorithms

online-algorithms is a skill for Claude Code, Codex from Arcadi4/nerdy. It costs 45 tokens per session (4,038 once invoked), scanned A, original, MIT.

A guide to algorithms that must make decisions before seeing future input, compared with an ideal method that knows the entire input in advance.

In plain words
What is it for?
Analyzing caching, paging, list updates, rent-or-buy choices, and randomized online methods using competitive analysis.
Why use it?
It provides the right way to measure decisions made without future knowledge, including how an adversary can expose weaknesses.

Skill for Claude CodeCodex

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/arcadi4/nerdy/online-algorithms
Any agent
npx skills add Arcadi4/nerdy --skill online-algorithms
Clone the repo
git clone --depth 1 https://github.com/Arcadi4/nerdy

Made for: Claude Code, Codex.

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 online-algorithms

README.md
[![agentmods](https://agentmods.dev/badge/skills/arcadi4/nerdy/online-algorithms.svg)](https://agentmods.dev/skills/arcadi4/nerdy/online-algorithms)
Your own site
<a href="https://agentmods.dev/skills/arcadi4/nerdy/online-algorithms"><img src="https://agentmods.dev/badge/skills/arcadi4/nerdy/online-algorithms.svg" alt="Measured on agentmods" height="20"></a>
Per session 45 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,038 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 $0.00045 $0.04038
Opus 5 $0.00023 $0.02019
Sonnet 5 $0.00009 $0.00808
Haiku 4.5 $0.00005 $0.00404

Measured 4d ago against content hash 5ccd75c6f264, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

online-algorithms 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.

clrs/online-algorithms/SKILL.md · 365 lines

How it starts

The opening of the file, as written. The whole thing — 365 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Online Algorithms

Overview

Online-algorithm answers must compare decisions made without future knowledge against an offline optimum that sees the entire input.

Core principle: never judge an online algorithm by its standalone worst case; judge the worst-case ratio between its cost and the cost of a future-knowing optimum under the same input model and adversary.

Shared CLRS Conventions

Follow the parent clrs skill for mathematical formatting, direct polished answers, theorem preconditions, and formula-free headings.

Answer Formatting Guardrail

Online-algorithm exercises often invite comparison tables. Do not put costs, thresholds, ratios, request sequences with symbolic block names, or potential-function expressions in table cells or inline code spans.

Use prose labels for cases, then put the associated expression in a display block immediately underneath. A safe pattern is:

  1. Name the case in words.
  2. State in prose which quantity is being computed.
  3. Put the cost, ratio, bound, or sequence in a display block.
  4. Return to prose for the interpretation.

If a verification answer needs a summary table, keep the table verbal only, such as "early arrival" and "ratio one," and put the exact expressions outside the table.

For elevator or ski-rental threshold answers, do not compress the case split to only the two dangerous ratios. Always name the harmless early-arrival piece first, then the just-after-give-up piece, then the late-arrival piece. The dangerous pieces determine the maximum, but the early piece confirms that the case split is complete.

When to Use

Use this skill for:

  • inputs revealed over time, including request sequences, releases, arrivals, or operation streams;
  • competitive-ratio proofs for minimization problems;
  • rent-or-buy or wait-then-switch strategies such as elevator, ski rental, and cow-path search;
  • self-organizing lists, list update, move-to-front, and adjacent-swap cost models;
  • online caching, paging, cache-eviction policies, marking algorithms, and adversarial lower bounds;
  • randomized online algorithms where the adversary model determines whether randomization helps.

Read the full file on GitHub · 365 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 · 365 lines · 45 tokens per session scan A 5ccd75c6f264

Subscribe to this mod's changes

online-algorithms is a skill published in the GitHub repository Arcadi4/nerdy (7 stars, last pushed 4mo ago), licensed MIT. It adds 45 tokens to every session and 4,038 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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