bio-alignment-sorting

A bioinformatics guide for reordering sequencing alignment files by genome position, read name, or a selected tag. BAM files store aligned sequencing reads in a compressed binary format.

In plain words
What is it for?
Preparing BAM files for indexing, visualization, variant calling, paired-end processing, mate fixing, and duplicate marking.
Why use it?
Many downstream tools require a particular read order, and paired-end processing often needs reads with matching names together.

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/gptomics/bioskills/alignment-sorting
Any agent
npx skills add GPTomics/bioSkills --skill alignment-sorting
Clone the repo
git clone --depth 1 https://github.com/GPTomics/bioSkills

Made for: Claude Code, Codex.

Per session 37 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,971 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. 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 $0.00037 $0.02971
Opus 5 $0.00018 $0.01486
Sonnet 5 $0.00007 $0.00594
Haiku 4.5 $0.00004 $0.00297

Measured 2d ago against content hash f425e08b3819, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

bio-alignment-sorting 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 2d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (examples/sort_pipeline.sh), 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.

Runs shell commandslowCapability

Expected in a hook, worth knowing in a rule or an instructions file.

subprocess.run(
Origin

Copies of this mod

1 near-identical copy found in the catalogue:

alignment-files/alignment-sorting/SKILL.md · 323 lines

How it starts

The opening of the file, as written. The whole thing — 323 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 Sorting

Sort alignment files by coordinate or read name using samtools and pysam.

"Sort a BAM file" -> Reorder reads by genomic coordinate (for indexing/variant calling) or by name (for paired-end processing).

  • CLI: samtools sort -o sorted.bam input.bam
  • Python: pysam.sort('-o', 'sorted.bam', 'input.bam')

Sort Orders

Order Flag Use Case
Coordinate default Indexing, visualization, variant calling
Name -n Paired-end processing, fixmate, markdup
Tag -t TAG Sort by specific tag value

samtools sort

Sort by Coordinate (Default)

samtools sort -o sorted.bam input.bam

Sort by Read Name

samtools sort -n -o namesorted.bam input.bam

Multi-threaded Sorting

samtools sort -@ 8 -o sorted.bam input.bam

Control Memory Usage

samtools sort -m 4G -@ 4 -o sorted.bam input.bam

Set Temporary Directory

samtools sort -T /tmp/sort_tmp -o sorted.bam input.bam

Specify Output Format

# Output as BAM (default)
samtools sort -O bam -o sorted.bam input.bam

# Output as CRAM
samtools sort -O cram --reference ref.fa -o sorted.cram input.bam

Sort by Tag

# Sort by cell barcode (10x Genomics)
samtools sort -t CB -o sorted_by_barcode.bam input.bam

Pipe from Aligner

bwa mem ref.fa reads.fq | samtools sort -o aligned.bam

samtools collate vs sort -n

Tool Algorithm Speed Memory Output guarantee
sort -n Full lexicographic sort by QNAME Slowest Spills to -T Strict total order by name
collate Hash-bucket grouping ~3-10x faster Bounded Mates adjacent; between-mate order undefined

Read the full file on GitHub · 323 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. 2d ago First seen · 323 lines · 37 tokens per session scan A f425e08b3819

Subscribe to this mod's changes

bio-alignment-sorting is a skill published in the GitHub repository GPTomics/bioSkills (1,198 stars, last pushed 17d ago), licensed MIT. It adds 37 tokens to every session and 2,971 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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