fastcontext-explorer

fastcontext-explorer is a skill for Claude Code, Codex from Jakevin/fastcontext-agent-tools. It costs 130 tokens per session (832 once invoked), scanned A, original, MIT.

A read-only code exploration helper that guides an agent through an unfamiliar repository. It searches across files and traces how parts of the code depend on one another before changes or explanations are made.

In plain words
What is it for?
Use it to locate symbols, follow requests through modules, map dependencies, identify affected tests and files, or investigate a bug.
Why use it?
It helps the agent find relevant files and call paths instead of relying on guesses when a task spans multiple files.

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/jakevin/fastcontext-agent-tools/fastcontext-explorer
Any agent
npx skills add Jakevin/fastcontext-agent-tools --skill fastcontext-explorer
Clone the repo
git clone --depth 1 https://github.com/Jakevin/fastcontext-agent-tools

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 fastcontext-explorer

README.md
[![agentmods](https://agentmods.dev/badge/skills/jakevin/fastcontext-agent-tools/fastcontext-explorer.svg)](https://agentmods.dev/skills/jakevin/fastcontext-agent-tools/fastcontext-explorer)
Your own site
<a href="https://agentmods.dev/skills/jakevin/fastcontext-agent-tools/fastcontext-explorer"><img src="https://agentmods.dev/badge/skills/jakevin/fastcontext-agent-tools/fastcontext-explorer.svg" alt="Measured on agentmods" height="20"></a>
Per session 130 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 832 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 $0.00130 $0.00832
Opus 5 $0.00065 $0.00416
Sonnet 5 $0.00026 $0.00166
Haiku 4.5 $0.00013 $0.00083

Measured 4d ago against content hash a1c37b0273e5, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fastcontext-explorer 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.

skills/fastcontext-explorer/SKILL.md · 102 lines

How it starts

The opening of the file, as written. The whole thing — 102 lines — stays where its author put it; the contents beside it link to each section on GitHub.

FastContext Explorer

Workflow

  1. Check availability first with the MCP tool fastcontext_health.
  2. If health is usable, call fastcontext_explore with a specific query and the repository root.
  3. Treat returned citations as candidate evidence, not proof. Read the cited files and line ranges yourself before editing or answering.
  4. If citations are sparse, off-target, or missing, refine the query once with concrete terms from the task, error, subsystem, or nearby filenames.
  5. For debugging poor searches, use fastcontext_explore_with_trace and inspect the saved trajectory.

When to Use

  • Understand unfamiliar code before editing, reviewing, debugging, or explaining it.
  • Trace logic across layers, such as request to handler to service to storage.
  • Answer code questions like "How does X work?", "Where is Y defined?", or "What calls Z?".
  • Map what a symbol depends on or what depends on it.
  • Assess which files are likely affected by a change.

When unsure and the answer needs more than one file, run FastContext first.

When Not to Use

  • You already read the exact file and surrounding context in this session.
  • One known file and one obvious search will answer the question.
  • The task is pure writing or generation with no repository exploration.
  • The task is non-code.

Query Shape

Write concise exploration requests that name behavior and intent:

Find where OAuth access tokens are refreshed and which tests cover expired token handling.

Prefer subsystem and failure language over generic searches:

Locate the request validation path that rejects oversized uploaded files.

Avoid asking FastContext to solve or patch:

Fix the upload bug.

MCP Tools

Use fastcontext_explore:

{
  "repo_path": "/absolute/path/to/repo",
  "query": "Locate the request validation path that rejects oversized uploaded files.",
  "max_turns": 6,
  "citation": true
}

Use fastcontext_explore_with_trace when a trajectory is needed:

Read the full file on GitHub · 102 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. 4d ago First seen · 102 lines · 130 tokens per session scan A a1c37b0273e5

Subscribe to this mod's changes

fastcontext-explorer is a skill published in the GitHub repository Jakevin/fastcontext-agent-tools (19 stars, last pushed 2mo ago), licensed MIT. It adds 130 tokens to every session and 832 once invoked, about $0.0006 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 2026-08-30.

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