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Agent skill

Marking Experimental APIs

by Fallout-build in Fallout-build/Fallout

How to mark a public API as not-yet-stable with [Experimental("FALLOUT0xx")], or deprecate one with [Obsolete(..., DiagnosticId = "FALLOUTOBS0xx")], including diagnostic-ID allocation.

Custom licenceAuto-check passed

Install Marking Experimental APIs

skills CLI
$ npx skills add Fallout-build/Fallout --skill marking-experimental-apis -a claude-code

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

GitHub CLI
$ gh skill install Fallout-build/Fallout marking-experimental-apis --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/Fallout-build/Fallout.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/marking-experimental-apis .claude/skills/marking-experimental-apis && 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
marking-experimental-apis
GitHub stars
167
Token cost
~917 tokens
SKILL.md length
360 words
Files
1
Skills in repo
8
Repo updated
First seen
Licence
Custom licence

At a glance

How to mark a public API as not-yet-stable with [Experimental("FALLOUT0xx")], or deprecate one with [Obsolete(..., DiagnosticId = "FALLOUTOBS0xx")], including diagnostic-ID allocation.

  • Adding public API that isnt ready for a stability guarantee
  • SKILL.md covers [Experimental] — opt-in… and [Obsolete] — deprecating a…
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
  • Removing/replacing/deprecating an existing public API

What it does

Marking Experimental APIs is an agent skill from Fallout-build/Fallout. How to mark a public API as not-yet-stable with [Experimental("FALLOUT0xx")], or deprecate one with [Obsolete(..., DiagnosticId = "FALLOUTOBS0xx")], including diagnostic-ID allocation. Trigger when adding public API that isn't ready for a stability guarantee, or removing/replacing/deprecating an existing public API.

Its SKILL.md is about 920 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

The repository describes itself as: ☢️ Fallout — The C/.NET Build System.

When your agent uses it

  • Adding public API that isnt ready for a stability guarantee
  • Removing/replacing/deprecating an existing public API

Example prompts

  • “FALLOUT0xx”
  • “FALLOUTOBS0xx”
  • “/marking-experimental-apis”

What it can do on your machine

Read from SKILL.md and the folder at commit 8333cc8. 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 csharp).

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

  • Network

    Links to these hosts (documentation or services it may open):

    • learn.microsoft.com

    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.

Context cost

Marking Experimental APIs loads about 917 tokens when it runs. Until then it costs about 86 tokens; SKILL.md has 360 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~86
When it runs · the whole SKILL.md, loaded when a task matches
~917

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

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 360 words (~917 tokens).

“Fallout has two attributes for public-surface churn, each with its own diagnostic-ID sequence and registry. Never mix the two sequences.”

— opening of SKILL.md by Fallout-build, Custom licence
name
marking-experimental-apis

Read the full SKILL.md on GitHub

Files

Just SKILL.md in .agents/skills/marking-experimental-apis of Fallout-build/Fallout.

Open the folder on GitHubat commit 8333cc8

Compare with similar skills

Marking Experimental APIs 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.

Marking Experimental APIs compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Marking Experimental APIs this skillFallout-build/Fallout167—~917Automated safety check: PassCustom licence
Stable Baselines3K-Dense-AI/scientific-agent-skills48k1 repos~3.7kAutomated safety check: NotesMIT
Experimental Designaiming-lab/AutoResearchClaw15k—~286Automated safety check: PassMIT
Stable Baselines3davila7/claude-code-templates32k8 repos~2.4kAutomated safety check: PassMIT
AI Provenance Mark Removerguillaumemeyer/watermarks-remover24k—~4.9kAutomated safety check: PassMIT
Experimentationcbrock84/headcount2k—~971Automated safety check: PassMIT

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Questions about Marking Experimental APIs

What does Marking Experimental APIs do?

How to mark a public API as not-yet-stable with [Experimental("FALLOUT0xx")], or deprecate one with [Obsolete(..., DiagnosticId = "FALLOUTOBS0xx")], including diagnostic-ID allocation. Marking Experimental APIs is an agent skill from Fallout-build/Fallout., DiagnosticId = "FALLOUTOBS0xx")], including diagnostic-ID allocation.

When should I use Marking Experimental APIs?

Marking Experimental APIs fits situations like: adding public API that isnt ready for a stability guarantee; removing/replacing/deprecating an existing public API.

How do I install Marking Experimental APIs in Claude Code?

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

How do I install Marking Experimental APIs in Codex?

Run `npx skills add Fallout-build/Fallout --skill marking-experimental-apis -a codex`. Or copy the skill folder (.agents/skills/marking-experimental-apis in Fallout-build/Fallout) into .agents/skills/marking-experimental-apis in your project. Codex loads it when a task matches its description.

Can I use Marking Experimental APIs 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 Fallout-build/Fallout --skill marking-experimental-apis -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/marking-experimental-apis, .gemini/skills/marking-experimental-apis, .github/skills/marking-experimental-apis and .opencode/skills/marking-experimental-apis in your project.

What does Marking Experimental APIs need to run?

SKILL.md names no scripts, command-line tools or credentials: Marking Experimental APIs is instructions for the agent only.

Does Marking Experimental APIs access the network?

SKILL.md names 1 domain. As links in the text: learn.microsoft.com. This is read from the text; nothing was executed.

Is Marking Experimental APIs 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 Marking Experimental APIs use?

Marking Experimental APIs has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.

How many tokens does Marking Experimental APIs use?

About 917 tokens (SKILL.md is roughly 3.7k 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 Marking Experimental APIs?

Skills that share tags, products or a category with Marking Experimental APIs: Stable Baselines3 (K-Dense-AI/scientific-agent-skills, 48k stars), Experimental Design (aiming-lab/AutoResearchClaw, 15k stars), Stable Baselines3 (davila7/claude-code-templates, 32k stars) and AI Provenance Mark Remover (guillaumemeyer/watermarks-remover, 24k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Marking Experimental APIs?

Fallout-build (a GitHub organization) maintains it in Fallout-build/Fallout, which has 167 GitHub stars. The repository holds 8 skills in this directory. The repository was last updated on October 3, 2026.

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