api-client

A design pattern for integrating an external HTTP API by separating a thin API client from an application service that applies business rules.

In plain words
What is it for?
Use it when adding services such as payment, messaging, or repository APIs, with raw responses handled by the client and application results by the service.
Why use it?
It keeps vendor-specific responses and network code separate from application logic, making the integration easier to maintain and test.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/ocbunknown/fastapi-claude-template/api-client
Any agent
npx skills add ocbunknown/fastapi-claude-template --skill api-client
Clone the repo
git clone --depth 1 https://github.com/ocbunknown/fastapi-claude-template

Made for: Claude Code, Codex.

Per session 102 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,217 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00102 $0.04217
Opus 5 $0.00051 $0.02108
Sonnet 5 $0.00020 $0.00843
Haiku 4.5 $0.00010 $0.00422

Measured 2d ago against content hash 8d86170be610, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

api-client 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 2d 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.

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.

.claude/skills/api-client/SKILL.md · 390 lines

How it starts

The opening of the file, as written. The whole thing — 390 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Integrating an external HTTP API

An external API integration is two objects, not one:

  1. Client (infrastructure/http/clients/<vendor>/) — thin HTTP wrapper. Returns raw vendor-shaped Pydantic models that mirror the API's JSON 1:1. No business logic, no transformation, no domain types.
  2. Service (application/v1/services/<vendor>.py) — holds a Client via its port, calls it, and maps raw responses into application Result types. All business rules (enum mapping, filtering, multi-call orchestration) live here. The service never returns Create*Type / Update*Type — persistence shape is the use case's job.

Use cases depend on the Service. In rare cases (debug/proxy/admin) they can depend on the Client port directly. Examples below use a Stripe-shaped payment provider — substitute your vendor.

Layer split

The project's rule (CLAUDE.md): application/ cannot import from infrastructure/; infrastructure/ can import from application/. Every type application-code reads must live in application/.

src/
├── application/
│   ├── common/interfaces/<vendor>/
│   │   ├── port.py              ← Protocol <Vendor>Client
│   │   ├── types.py             ← VENDOR enums/literals
│   │   └── responses.py         ← raw Pydantic DTOs (1:1 with API JSON)
│   ├── v1/results/<entity>.py   ← application Result (PaymentResult, …)
│   └── v1/services/<vendor>.py  ← <Vendor>Service: raw → Result
│
└── infrastructure/http/clients/<vendor>/
    ├── client.py                ← <Vendor>API(Client) — implements port structurally
    └── endpoints.py              ← StrEnum of URL paths

Raw response DTOs and vendor enums live in application/ because the service in application reads them. They become part of the port contract — the same pattern as JWT/TokenType, Cache/CacheKey: the port owns its vocabulary.

The Client — raw and dumb

Jobs: know the vendor's URL/auth, send HTTP, parse JSON into application-defined DTOs, translate HTTP errors into application exceptions. Never contains business branching or domain types.

Read the full file on GitHub · 390 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. 2d ago First seen · 390 lines · 102 tokens per session scan A 8d86170be610

Subscribe to this mod's changes

api-client is a skill published in the GitHub repository ocbunknown/fastapi-claude-template (32 stars, last pushed 4mo ago), licensed MIT. It adds 102 tokens to every session and 4,217 once invoked, about $0.0005 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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