context-fundamentals

context-fundamentals is a skill for Claude Code, Codex from docxology/template. It costs 125 tokens per session (3,183 once invoked), scanned A, a copy of context-fundamentals, Apache-2.0.

A guide to the information an AI model can use while answering, including instructions, conversation history, retrieved files, and tool results. Context engineering means selecting the most useful information for the task.

In plain words
What is it for?
Use it to understand context windows, how attention is distributed, and the basic ideas behind managing information for AI agents.
Why use it?
It explains why more information is not always better and how misplaced or conflicting details can make an AI answer less reliable.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions subagents; installed under .agents/ (shared by several agents).

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/docxology/template/context-fundamentals
Any agent
npx skills add docxology/template --skill context-fundamentals
Clone the repo
git clone --depth 1 https://github.com/docxology/template

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 context-fundamentals

README.md
[![agentmods](https://agentmods.dev/badge/skills/docxology/template/context-fundamentals.svg)](https://agentmods.dev/skills/docxology/template/context-fundamentals)
Your own site
<a href="https://agentmods.dev/skills/docxology/template/context-fundamentals"><img src="https://agentmods.dev/badge/skills/docxology/template/context-fundamentals.svg" alt="Measured on agentmods" height="20"></a>
Per session 125 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,183 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 100% copy Near-identical to another mod 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 5.1 $0.00125 $0.03183
Opus 5 $0.00063 $0.01591
Sonnet 5 $0.00025 $0.00637
Haiku 4.5 $0.00013 $0.00318

Measured 6d ago against content hash 03b56e1c40ed, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

context-fundamentals 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 6d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/context_manager.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

Origin

This is a copy

100% identical to context-fundamentals — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.agents/skills/context-fundamentals/SKILL.md · 211 lines

How it starts

The opening of the file, as written. The whole thing — 211 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Context Engineering Fundamentals

Context is the complete state available to a language model at inference time: system instructions, tool definitions, retrieved documents, message history, and tool outputs. Context engineering is the discipline of curating the smallest high-signal token set that maximizes the likelihood of desired outcomes.

This skill is the conceptual foundation that every other skill in the collection builds on. It explains what context is, how attention mechanics work, why context quality matters more than quantity, and the mental models needed to interpret every other context-engineering decision. It does not own operational work: debugging attention failures belongs to context-degradation, token-efficiency tactics belong to context-optimization, conversation summarization belongs to context-compression, file-based offloading belongs to filesystem-context, and project-shape decisions belong to project-development.

When to Activate

Activate this skill when the work is conceptual:

  • Explaining what context is and how attention mechanics constrain agent behavior.
  • Onboarding new contributors who need the mental models before diving into operational skills.
  • Reasoning about a context-related design decision from first principles (what does this constraint mean, why does this trade-off exist) before picking a specific tactic.
  • Writing or reviewing documentation that needs to ground operational guidance in the underlying mechanics.

Do not activate this skill for operational work. The specialized skills handle the doing:

  • Diagnosing lost-in-middle, context poisoning, or attention failures: context-degradation.
  • Reducing token cost via masking, partitioning, prefix caching, budgets: context-optimization.
  • Compressing a long session into a handoff summary: context-compression.
  • Offloading large tool outputs or maintaining a durable scratchpad: filesystem-context.
  • Deciding the shape of an LLM project or pipeline: project-development.

Read the full file on GitHub · 211 lines

Files

What ships with it

2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 6d ago First seen · 211 lines · 125 tokens per session scan A 03b56e1c40ed

Subscribe to this mod's changes

context-fundamentals is a skill published in the GitHub repository docxology/template (19 stars, last pushed yesterday), licensed Apache-2.0. It adds 125 tokens to every session and 3,183 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to context-fundamentals, differing in 0 lines, and is treated as a copy.

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