bio-alignment-indexing

bio-alignment-indexing is a skill for Claude Code, Codex from PKU-YuanGroup/OpenAI4S. It costs 41 tokens per session (2,878 once invoked), scanned A, a copy of bio-alignment-indexing, MIT.

A tool for creating index files for BAM, CRAM, and related alignment files. An index lets software jump directly to reads from a chosen region of a genome instead of reading the entire file.

In plain words
What is it for?
Use it to index alignment files with samtools or pysam, then fetch reads from specific genes, chromosomes, or genomic regions.
Why use it?
It makes region-based access possible and avoids scanning large alignment files from start to finish. The available index type depends on the file format and chromosome or contig size.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: positional $N argument.

Good fit Use it to index alignment files with samtools or pysam, then fetch reads from specific genes, chromosomes, or genomic regions.

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Install with agentmods
npx agentmods add skills/pku-yuangroup/openai4s/bio-alignment-files-alignment-indexing
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.

Any agent
npx skills add PKU-YuanGroup/OpenAI4S --skill bio-alignment-files-alignment-indexing
Clone the repo
git clone --depth 1 https://github.com/PKU-YuanGroup/OpenAI4S

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 bio-alignment-indexing

README.md
[![agentmods](https://agentmods.dev/badge/skills/pku-yuangroup/openai4s/bio-alignment-files-alignment-indexing/github.svg)](https://agentmods.dev/skills/pku-yuangroup/openai4s/bio-alignment-files-alignment-indexing)
Your own site
<a href="https://agentmods.dev/skills/pku-yuangroup/openai4s/bio-alignment-files-alignment-indexing"><img src="https://agentmods.dev/badge/skills/pku-yuangroup/openai4s/bio-alignment-files-alignment-indexing/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for bio-alignment-indexing

Your own site · 80×15
<a href="https://agentmods.dev/skills/pku-yuangroup/openai4s/bio-alignment-files-alignment-indexing"><img src="https://agentmods.dev/badge/skills/pku-yuangroup/openai4s/bio-alignment-files-alignment-indexing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 41 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,878 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
Origin 95% 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 $0.00041 $0.02878
Opus 5 $0.00020 $0.01439
Sonnet 5 $0.00008 $0.00576
Haiku 4.5 $0.00004 $0.00288

Measured 12d ago against content hash 1a0155e83a68, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

bio-alignment-indexing scanned grade A with 1 finding 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 12d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/fetch_regions.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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

count = sum(1 for _ in bam.fetch(chrom, start, end))
Origin

This is a copy

95% identical to bio-alignment-indexing — 12 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.

skills/bioskills/bio-alignment-files-alignment-indexing/SKILL.md · 320 lines

How it starts

The opening of the file, as written. The whole thing — 320 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Version Compatibility

Reference examples tested with: pysam 0.22+, samtools 1.19+

Before using code patterns, verify installed versions match. If versions differ:

  • Python: pip show <package> then help(module.function) to check signatures
  • CLI: <tool> --version then <tool> --help to confirm flags

If code throws ImportError, AttributeError, or TypeError, introspect the installed package and adapt the example to match the actual API rather than retrying.

Alignment Indexing

Create indices for random access to alignment files using samtools and pysam.

"Index a BAM file" -> Create a .bai/.csi index enabling random access to genomic regions.

  • CLI: samtools index file.bam
  • Python: pysam.index('file.bam')

Index Types

Index Extension Max contig Bin shift When required
BAI .bai / .bam.bai 2^29 bp ≈ 537 Mbp fixed (16 kb) Default for human, mouse, fly, fish
CSI .csi / .bam.csi 2^(min_shift + depth*3) configurable via -m Required for any contig >537 Mbp
CRAI .crai / .cram.crai chunk-based n/a CRAM only
TBI .tbi 2^29-1 fixed tabix VCF/BED -- same limit as BAI

Which Index for Which Genome

Genome Largest contig Index
GRCh38 / GRCh37 (human) 248 Mbp BAI
GRCm39 (mouse) 195 Mbp BAI
GRCz11 (zebrafish), TAIR10 (Arabidopsis) 78 Mbp / 30 Mbp BAI
Wheat IWGSC (Triticum aestivum) ~830 Mbp (chr3B) CSI
Pine, fir, axolotl, sugar pine multi-Gbp CSI with larger -m
Long-read assembly with very large contigs varies check cut -f2 ref.fa.fai | sort -nr | head -1

For polyploid plants and salamander-scale genomes, increase the bin shift:

# Default CSI matches BAI bin layout: 2^(14 + 5*3) = 2^29 bp ≈ 537 Mbp per contig
samtools index -c file.bam

# Larger min_shift for contigs >537 Mbp (wheat, axolotl, sugar pine)
samtools index -c -m 18 file.bam   # 2^(18+15) = 2^33 = ~8.5 Gbp per contig

Read the full file on GitHub · 320 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. 12d ago First seen · 320 lines · 41 tokens per session scan A 1a0155e83a68

Subscribe to this mod's changes

bio-alignment-indexing is a skill published in the GitHub repository PKU-YuanGroup/OpenAI4S (407 stars, last pushed yesterday), licensed MIT. It adds 41 tokens to every session and 2,878 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). It is 95% identical to bio-alignment-indexing, differing in 12 lines, and is treated as a copy.

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