bio-alignment-amplicon-clipping

bio-alignment-amplicon-clipping is a skill for Claude Code, Codex from GPTomics/bioSkills. It costs 71 tokens per session (2,369 once invoked), scanned A, original, MIT.

A guide to removing PCR primer sequences from DNA sequencing alignment files. PCR primers are short laboratory-made sequences used to copy target regions, and can look like real biological DNA if left in the data.

In plain words
What is it for?
Use it to trim primer footprints from amplicon sequencing data, including SARS-CoV-2, cancer, fusion, and other targeted panels, using a primer BED file.
Why use it?
Untrimmed primer sequences can falsely confirm the reference genome or hide real mutations at primer locations. Clipping them makes the aligned reads more accurate for analysis.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to trim primer footprints from amplicon sequencing data, including SARS-CoV-2, cancer, fusion, and other targeted panels, using a primer BED file.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/gptomics/bioskills/alignment-amplicon-clipping
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 alignment-amplicon-clipping
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-alignment-amplicon-clipping

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

Your own site · 80×15
<a href="https://agentmods.dev/skills/gptomics/bioskills/alignment-amplicon-clipping"><img src="https://agentmods.dev/badge/skills/gptomics/bioskills/alignment-amplicon-clipping.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 71 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,369 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 $0.00071 $0.02369
Opus 5 $0.00036 $0.01184
Sonnet 5 $0.00014 $0.00474
Haiku 4.5 $0.00007 $0.00237

Measured 9d ago against content hash e87d3d0b41ad, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

bio-alignment-amplicon-clipping 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 1 executable file (examples/ampliconclip_workflow.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.

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/alignment-amplicon-clipping/SKILL.md · 159 lines

How it starts

The opening of the file, as written. The whole thing — 159 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Version Compatibility

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

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 Amplicon Clipping

"Trim primer-derived bases from amplicon BAM" -> Soft- or hard-clip the 5' primer footprint after alignment using a primer BED, then repair fixmate/MD/NM tags.

  • CLI: samtools ampliconclip -b primers.bed input.bam -o clipped.bam (since samtools 1.11)
  • Alternative: iVar trim, BAMClipper, fgbio ClipBam

Why Primer Trimming After Alignment

Amplicon panels (SARS-CoV-2 ARTIC, hereditary cancer panels, ctDNA hot-spot panels, fusion panels, 16S rRNA) use designed PCR primers for enrichment. Primer-derived bases at read 5' ends do NOT reflect biological sequence -- they reflect the primer template. Without trimming:

  • False reference confirmation at primer footprint positions.
  • Variant allele frequency suppressed at variants under primers (the primer sequence cannot capture the variant base).
  • Strand bias artifacts (primers are typically one-strand).

Standard amplicon BAMs should NEVER be processed by samtools markdup -- by design every read at a primer location is a "duplicate" by coordinate. See duplicate-handling for the assay-aware decision.

Tool Selection

Tool When Notes
samtools ampliconclip Default for amplicon panels (since 1.11) Soft- or hard-clip from BED; modifies CIGAR; invalidates MD/NM
iVar trim Illumina SARS-CoV-2 / PrimalSeq route (Andersen lab) Coordinates by primer name/position; soft-clips only + quality sliding-window
BAMClipper Capture / hybrid panels with primer overlap 5'-end clipping with overlap handling
fgbio ClipBam When read-pair coordination matters Soft/hard-clip with mate-aware end adjustment
cutadapt (pre-alignment) Legacy / when alignment is downstream Trims at FASTQ stage; less precise for amplicon

Read the full file on GitHub · 159 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. 9d ago First seen · 159 lines · 71 tokens per session scan A e87d3d0b41ad

Subscribe to this mod's changes

bio-alignment-amplicon-clipping is a skill published in the GitHub repository GPTomics/bioSkills (1,199 stars, last pushed 25d ago), licensed MIT. It adds 71 tokens to every session and 2,369 once invoked, about $0.0004 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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