fusebase-flow: Skill for Claude Code

.agents/skills/app-backend/SKILL.md

app-backend is a skill for Claude Code from fusebase-dev/fusebase-flow. It costs 92 tokens per session (11,978 once invoked), scanned A, original, MIT.

A guide to adding a server-side backend to Fusebase Apps, including web APIs, live WebSocket connections, and scheduled jobs. The backend is the part of an application that runs on a server rather than in the user’s browser.

In plain words
What is it for?
Use it when adding REST endpoints, WebSockets, scheduled tasks, backend folders, authentication-related storage, or other server-side behavior.
Why use it?
It explains how to keep data separate for different users and avoid accidentally sharing credentials or settings between them.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: installed under .agents/ (shared by several agents).

This is fusebase-dev/fusebase-flow's own configuration. It tells Claude Code how to work on fusebase-flow itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything fusebase-flow configures →

Part of the fusebase-flow plugin — 56 skills, 8 commands, 4 agents shipped together

Reuse

Borrowing it

Nothing to install: this file belongs to fusebase-dev/fusebase-flow. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/fusebase-dev/fusebase-flow/main/.agents/skills/app-backend/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/fusebase-dev/fusebase-flow

Made for: Claude Code.

Or install fusebase-flow, the plugin that ships this one along with the rest of its 56 skills, 8 commands, 4 agents.

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 app-backend

README.md
[![agentmods](https://agentmods.dev/badge/skills/fusebase-dev/fusebase-flow/app-backend/github.svg)](https://agentmods.dev/skills/fusebase-dev/fusebase-flow/app-backend)
Your own site
<a href="https://agentmods.dev/skills/fusebase-dev/fusebase-flow/app-backend"><img src="https://agentmods.dev/badge/skills/fusebase-dev/fusebase-flow/app-backend/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 app-backend

Your own site · 80×15
<a href="https://agentmods.dev/skills/fusebase-dev/fusebase-flow/app-backend"><img src="https://agentmods.dev/badge/skills/fusebase-dev/fusebase-flow/app-backend.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 92 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 11,978 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 6 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Privilege Escalation · line 382
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 798
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 820
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • medium Server-Side Request Forgery · line 76
    Code issues a request to a loopback, link-local, or private-range host. This can reach internal services not meant to be exposed and is a common SSRF pivot.
    Fix: Avoid requests to loopback/link-local/private hosts from skill code. If internal access is intended, document it and validate the target against an allowlist.
  • medium Excessive Agency · line 381
    Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.
    Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.
  • medium Excessive Agency · line 926
    Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.
    Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.
How audits are shown
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 $0.00092 $0.11978
Opus 5.5 $0.00037 $0.04791
Sonnet 5.5 $0.00018 $0.02396
Haiku 4.5 $0.00009 $0.01198

Measured 2mo ago against content hash 137e7b07cb35, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

app-backend 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 2mo ago.

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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

When the app needs to receive webhooks from a third-party service (Asana, GitHub, Stripe, Monday, etc.), register the subscription with that provider **yourself** as part of the deploy — do not hand the user a `curl` / a
Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.agents/skills/app-backend/SKILL.md · 976 lines

How it starts

The opening of the file, as written. The whole thing — 976 lines — stays where its author put it; the contents beside it link to each section on GitHub.

App Backend

Multi-User Architecture

Apps are always multi-user. The backend serves requests from many users concurrently. Every design decision must account for this.

Per-user vs. shared state:

Storage Scope Use for
httpOnly cookies Per-user (per browser) OAuth tokens, user preferences, session data
Dashboard rows (keyed by user ID) Per-user (persistent) User settings, saved state
Fusebase secrets / env vars Shared (all users) API keys, service-account credentials
In-memory variables Shared (all users, lost on restart) Short-lived caches only

Common mistakes:

  • ❌ Storing a user's OAuth token in an env var or in-memory config → all users share one token
  • ❌ Storing a user's preference in a module-level variable → last user's preference wins for everyone
  • ❌ Using env vars for per-user settings or selections → same value for everyone
  • ❌ Using session/token-derived values (ft:*, JWT pieces, rotating token IDs) as persistent row partition keys
  • ✅ Store per-user data in cookies or dashboard rows keyed by user
  • ✅ Use env vars only for credentials/config shared across all users (e.g. OAuth client ID/secret)

Stable key as partition key (required)

For any persisted per-user data, derive the partition key from stable identity only:

  • Use userId/orgUserId from a stable identity endpoint (getMe-style call)
  • Normalize to a canonical key (example: user:<userId>) in one helper
  • Use the same key on all read/write paths

Do not derive partition keys from runtime app/session tokens. Tokens rotate, so token-derived keys cause "missing records after relogin" while data still exists under old keys.

Read the full file on GitHub · 976 lines

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. 2mo ago First seen · 976 lines · 92 tokens per session scan A 137e7b07cb35

Subscribe to this mod's changes

app-backend is a skill published in the GitHub repository fusebase-dev/fusebase-flow (9 stars, last pushed 13d ago), licensed MIT. It adds 92 tokens to every session and 11,978 once invoked, about $0.0004 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Related

app-backend compared with skills from other repositories

app-backend next to 6 skills from other repositories
ModTypeStarsLast pushLicenceScanTokensWorks with
app-backendfusebase-dev/fusebase-flowSkill913d agoMITA92Claude Code
adobe-express-cors-and-backendSandgrouse/adobe-express-dev-skillSkill92mo agononeA92Claude Code, Codex
adobe-express-oauth-authenticationSandgrouse/adobe-express-dev-skillSkill92mo agononeA50Claude Code, Codex
lov-optimize-tauri-backendlovstudio/skillsSkill72yesterdayMITA71Claude Code
lov-cli-creatorlovstudio/skillsSkill72yesterdayMITA58Claude Code
lov-api-creatorlovstudio/skillsSkill72yesterdayMITA75Claude Code
lov-cli2anythinglovstudio/skillsSkill72yesterdayMITA55Claude Code