bio-sam-bam-basics

bio-sam-bam-basics is a skill for Claude Code, Codex from GPTomics/bioSkills. It costs 45 tokens per session (4,212 once invoked), scanned A, original, MIT.

A bioinformatics guide for viewing, converting, and understanding SAM, BAM, and CRAM files, which store sequencing reads aligned to a reference genome. SAM is readable text, BAM is compressed binary data, and CRAM is smaller reference-based storage.

In plain words
What is it for?
Opening alignments, viewing reads and their coordinates or quality fields, and converting between SAM, BAM, and CRAM.
Why use it?
It explains the formats and gives commands or Python examples for inspecting aligned reads without treating the files as plain text.

Skill for Claude CodeCodex

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

Good fit Opening alignments, viewing reads and their coordinates or quality fields, and converting between SAM, BAM, and CRAM.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/gptomics/bioskills/sam-bam-basics
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 GPTomics/bioSkills --skill sam-bam-basics
Clone the repo
git clone --depth 1 https://github.com/GPTomics/bioSkills

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-sam-bam-basics

README.md
[![agentmods](https://agentmods.dev/badge/skills/gptomics/bioskills/sam-bam-basics/github.svg)](https://agentmods.dev/skills/gptomics/bioskills/sam-bam-basics)
Your own site
<a href="https://agentmods.dev/skills/gptomics/bioskills/sam-bam-basics"><img src="https://agentmods.dev/badge/skills/gptomics/bioskills/sam-bam-basics/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-sam-bam-basics

Your own site · 80×15
<a href="https://agentmods.dev/skills/gptomics/bioskills/sam-bam-basics"><img src="https://agentmods.dev/badge/skills/gptomics/bioskills/sam-bam-basics.svg" alt="Reviewed on agentmods" width="80" 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 4,212 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00045 $0.04212
Opus 5 $0.00023 $0.02106
Sonnet 5 $0.00009 $0.00842
Haiku 4.5 $0.00005 $0.00421

Measured 9d ago against content hash 068689b94981, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

bio-sam-bam-basics 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 9d ago.

The scan reads SKILL.md. This mod also ships 2 executable files (examples/convert_formats.sh, examples/view_bam.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

Copies of this mod

1 near-identical copy found in the catalogue:

alignment-files/sam-bam-basics/SKILL.md · 373 lines

How it starts

The opening of the file, as written. The whole thing — 373 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.

SAM/BAM/CRAM Basics

"Read a BAM file" -> Open a binary alignment file and iterate over aligned reads with their mapping coordinates, flags, and quality scores.

  • Python: pysam.AlignmentFile() (pysam)
  • CLI: samtools view (samtools)
  • R: scanBam() (Rsamtools)

View and convert alignment files using samtools and pysam.

Format Overview

Format Description Use Case
SAM Text format, human-readable Debugging, small files
BAM Binary compressed SAM Standard storage format
CRAM Reference-based compression Long-term archival, smaller than BAM

SAM Format Structure

@HD VN:1.6 SO:coordinate
@SQ SN:chr1 LN:248956422
@RG ID:sample1 SM:sample1
@PG ID:bwa PN:bwa VN:0.7.17
read1  0   chr1  100  60  50M  *  0  0  ACGT...  FFFF...  NM:i:0

Header lines start with @:

  • @HD - Header metadata (version, sort order)
  • @SQ - Reference sequence dictionary
  • @RG - Read group information
  • @PG - Program used to create file

Alignment fields (tab-separated):

  1. QNAME - Read name
  2. FLAG - Bitwise flag
  3. RNAME - Reference name
  4. POS - 1-based position
  5. MAPQ - Mapping quality
  6. CIGAR - Alignment description
  7. RNEXT - Mate reference
  8. PNEXT - Mate position
  9. TLEN - Template length
  10. SEQ - Read sequence
  11. QUAL - Base qualities
  12. Optional tags (NM:i:0, MD:Z:50, etc.)

samtools view

View BAM as SAM

samtools view input.bam | head

View with Header

samtools view -h input.bam | head -100

Read the full file on GitHub · 373 lines

Files

What ships with it

3 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. 9d ago First seen · 373 lines · 45 tokens per session scan A 068689b94981

Subscribe to this mod's changes

bio-sam-bam-basics is a skill published in the GitHub repository GPTomics/bioSkills (1,199 stars, last pushed 24d ago), licensed MIT. It adds 45 tokens to every session and 4,212 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 2026-08-30.

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