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Agent skill

Filter

by zalando in zalando/skipper

Create or modify code in the filters package and all its sub-folders

MITAuto-check passedDevOps & Cloud

Install Filter

skills CLI
$ npx skills add zalando/skipper --skill filter -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install zalando/skipper filter --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/zalando/skipper.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/filter .claude/skills/filter && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
filter
GitHub stars
3.3k
Token cost
~527 tokens
SKILL.md length
42 words
Files
1
Skills in repo
5
Repo updated
First seen
Licence
MIT

At a glance

Create or modify code in the filters package and all its sub-folders

  • DevOps & Cloud work in your project
  • SKILL.md covers What I do, When to use me and Quick start
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Filter is an agent skill from zalando/skipper. Create or modify code in the filters package and all its sub-folders

Its SKILL.md is about 530 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts. Compatibility notes: opencode, claude

It sits in DevOps & Cloud. It works with Kubernetes. The repository describes itself as: An HTTP router and reverse proxy for service composition, including use cases like Kubernetes Ingress. The licence is MIT.

When your agent uses it

  • DevOps & Cloud work in your project

Example prompts

  • “/filter”

Requirements

  • Compatibility (from SKILL.md): opencode, claude

What it can do on your machine

Read from SKILL.md and the folder at commit 4f6cd0a. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are go).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

  • Compatibility

    opencode, claude

    From compatibility in the SKILL.md frontmatter.

Context cost

Filter loads about 527 tokens when it runs. Until then it costs about 19 tokens; SKILL.md has 42 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~19
When it runs · the whole SKILL.md, loaded when a task matches
~527

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from zalando/skipper at commit 4f6cd0a, republished under its MIT licence (© zalando). 42 words, ~527 tokens.

Download SKILL.mdSave it as .claude/skills/filter/SKILL.md (or your agent's skills folder).
name
filter
description
Create or modify code in the filters package and all its sub-folders
compatibility
opencode, claude
license
MIT
metadata.audience
maintainers, contributors

What I do

  • Create filter code that is efficient and readable

When to use me

Use this when you are writing code in sub-folders of ./filters/

Quick start

A filter consists of 2 types spec and filter that implement 2 different interfaces:

go
// Spec objects are specifications for filters. When initializing the routes,
// the Filter instances are created using the Spec objects found in the
// registry.
type Spec interface {
	// Name gives the name of the Spec. It is used to identify filters in a route definition.
	Name() string

	// CreateFilter creates a Filter instance. Called with the parameters in the route
	// definition while initializing a route.
	CreateFilter(config []any) (Filter, error)
}
go
// Filter is created by the Spec components, optionally using filter
// specific settings. When implementing filters, it needs to be taken
// into consideration, that filter instances are route specific and not
// request specific, so any state stored with a filter is shared between
// all requests for the same route and can cause concurrency issues.
type Filter interface {
	// The Request method is called while processing the incoming request.
	Request(FilterContext)

	// The Response method is called while processing the response to be
	// returned.
	Response(FilterContext)
}```

The `CreateFilter(config []any) (Filter, error)` function is run at
routing tree creation time, so only once in a while. Everything we can
pre-compute to run a faster Filter execution the better. Here we
process input from developers or operators that might do mistakes. We
want to show errors clearly.

The `Filter` interface functions are running in the hotpath of the
request processing. Here we need to be very efficient and want to
reduce latency, increase throughput, minimize allocations and we run
heavily concurrent. Here we also process untrusted, maybe malicious
input.

© zalando, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/filter of zalando/skipper.

Open the folder on GitHubat commit 4f6cd0a

Compare with similar skills

Filter next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Filter compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Filter this skillzalando/skipper3.3k—~527Automated safety check: PassMIT
Kubeshark Installerkubeshark/kubeshark12k—~3.6kAutomated safety check: NotesApache-2.0
KubeSphere Multi-Tenant Managementkubesphere/kubesphere17k—~3.1kAutomated safety check: PassCustom licence
Sim Helmsimstudioai/sim30k—~2.2kAutomated safety check: PassApache-2.0
Helm Chart ScaffoldingCybereason-Public/owLSM28012 repos~381Automated safety check: PassGPL-2.0
Kubeshark KFL2 Filter Referencekubeshark/kubeshark12k—~3.6kAutomated safety check: PassApache-2.0

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Works with

Categories

Questions about Filter

What does Filter do?

Create or modify code in the filters package and all its sub-folders. Filter is an agent skill from zalando/skipper.

When should I use Filter?

Filter fits situations like: devOps & Cloud work in your project.

How do I install Filter in Claude Code?

Run `npx skills add zalando/skipper --skill filter -a claude-code`. Or copy the skill folder (.agents/skills/filter in zalando/skipper) into .claude/skills/filter in your project. Claude Code loads it when a task matches its description.

How do I install Filter in Codex?

Run `npx skills add zalando/skipper --skill filter -a codex`. Or copy the skill folder (.agents/skills/filter in zalando/skipper) into .agents/skills/filter in your project. Codex loads it when a task matches its description.

Can I use Filter in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add zalando/skipper --skill filter -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/filter, .gemini/skills/filter, .github/skills/filter and .opencode/skills/filter in your project.

What does Filter need to run?

SKILL.md names no scripts, command-line tools or credentials: Filter is instructions for the agent only. Compatibility (from SKILL.md): opencode, claude.

Does Filter access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Filter safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Filter use?

Filter is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Filter use?

About 527 tokens (SKILL.md is roughly 2.1k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Filter?

Skills that share tags, products or a category with Filter: Kubeshark Installer (kubeshark/kubeshark, 12k stars), KubeSphere Multi-Tenant Management (kubesphere/kubesphere, 17k stars), Sim Helm (simstudioai/sim, 30k stars) and Helm Chart Scaffolding (Cybereason-Public/owLSM, 280 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Filter?

zalando (a GitHub organization) maintains it in zalando/skipper, which has 3,331 GitHub stars. The repository holds 5 skills in this directory. The repository was last updated on October 6, 2026.

Source: zalando/skipper on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.