Building LLM-Powered Applications with Claude

This skill helps you build LLM-powered applications with Claude. Choose the right surface based on your needs, detect the project language, then read the relevant language-specific documentation.

Before You Start

Scan the target file (or, if no target file, the prompt and project) for non-Anthropic provider markers - import openai, from openai, langchain_openai, OpenAI(, gpt-4, gpt-5, file names like agent-openai.py or *-generic.py, or any explicit instruction to keep the code provider-neutral. If you find any, stop and tell the user that this skill produces Claude/Anthropic SDK code; ask whether they want to switch the file to Claude or want a non-Claude implementation. Do not edit a non-Anthropic file with Anthropic SDK calls. (Exception: the prompt-audit subcommand is non-interactive and does not stop here - it records non-Anthropic provider markers in its report's stated assumptions and never proposes switching a non-Anthropic file to the Anthropic SDK.)

Output Requirement

When the user asks you to add, modify, or implement a Claude feature, your code must call Claude through one of:

1. The official Anthropic SDK for the project's language (anthropic, @anthropic-ai/sdk, com.anthropic.*, etc.). This is the default whenever a supported SDK exists for the project.
2. Raw HTTP (curl, requests, fetch, httpx, etc.) - only when the user explicitly asks for cURL/REST/raw HTTP, the project is a shell/cURL project, or the language has no official SDK.

Never mix the two - don't reach for requests/fetch in a Python or TypeScript project just because it feels lighter. Never fall back to OpenAI-compatible shims.

Never guess SDK usage. Function names, class names, namespaces, method signatures, and import paths must come from explicit documentation - either the {lang}/ files in this skill or the official SDK repositories or documentation links listed in shared/live-sources.md. If the binding you need is not explicitly documented in the skill files, WebFetch the relevant SDK repo from shared/live-sources.md before writing code. Do not infer Ruby/Java/Go/PHP/C# APIs from cURL shapes or from another language's SDK.

If WebFetch or repository access fails (network restricted, timeouts, clone blocked): do not keep retrying - write code from the patterns and namespace/package tables in the {lang}/ file, run the compiler or interpreter on it, and iterate on the error output. For statically-typed SDKs (C#, Java, Go) a compile-fix loop against local errors reaches working code faster than blocked network research.

Defaults

Unless the user requests otherwise:

For the Claude model version, please use Claude Opus 5, which you can access via the exact model string claude-opus-5. Please default to using adaptive thinking (thinking: {type: "adaptive"}) for anything remotely complicated. And finally, please default to streaming for any request that may involve long input, long output, or high max_tokens - it prevents hitting request timeouts. Use the SDK's .get_final_message() / .finalMessage() helper to get the complete response if you don't need to handle individual stream events

Warning: API Drift - Your Training Prior May Be Stale

Several common Claude API shapes changed in 2025-2026. If you recall a pattern from training, verify it against the {lang}/ files in this skill before writing - the rows below are the most frequent drift points:

Area	Stale prior	Current API
Extended thinking	thinking: {type: "enabled", budget_tokens: N}	On Claude 4.6+ models: thinking: {type: "adaptive"}. budget_tokens is deprecated on Opus 4.6 / Sonnet 4.6 and rejected with a 400 on Fable 5/5.1 / Sonnet 5 / Opus 5 / 4.8 / 4.7. Pre-4.6 models still use budget_tokens.
Web search / web fetch tool type	web_search_20250305, web_fetch_20250910	web_search_20260209, web_fetch_20260209 (dynamic filtering) on Opus 5/4.8/4.7/4.6, Sonnet 5, and Sonnet 4.6. Older models keep the basic variants; on Vertex AI only basic web_search_20250305 is available (web fetch is not on Vertex) - see the Server Tools QR below.
PHP parameter names	snake_case wire names as named args (max_tokens)	Top-level named args are camelCase (maxTokens). Nested array keys vary by feature (e.g. 'taskBudget', 'skillID', 'mcp_server_name') - copy the exact key from the documented example; do not bulk-convert.
Managed Agents credentials	Keep secrets host-side via custom tools (the only option before vaults shipped)	Vault environment_variable credentials - stored by Anthropic, substituted at egress, never visible in the sandbox (shared/managed-agents-tools.md -> Vaults). Host-side custom tools remain the fallback for self-hosted sandboxes.
Files API / Skills	client.beta.files.* / client.beta.skills.* with beta files-api-2025-04-14 / skills-2025-10-02	Out of beta: client.files.* / client.skills.*, no beta header. In current SDKs client.beta.files / client.beta.skills have breaking shape changes from previous versions, matching the stable namespaces - migrate per shared/live-sources.md -> Files API / Skills Guide.

The {lang}/ files in this skill are authoritative over recalled patterns.

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Subcommands

If the User Request at the bottom of this prompt is a bare subcommand string (no prose), search every Subcommands table in this document - including any in sections appended below - and follow the matching Action column directly. This lets users invoke specific flows via /claude-api <subcommand>. If no table in the document matches, treat the request as normal prose.

Subcommand	Action
migrate	Migrate existing Claude API code to a newer model. Read shared/model-migration.md immediately and follow it in order: Step 0 (confirm scope - ask which files/directories before any edit), Step 1 (classify each file), then the per-target breaking-changes section. Do not summarize the guide - execute it. If the user did not name a target model, ask which model to migrate to in the same turn as the scope question. After the per-target changes are applied, audit the in-scope prompt text, tool descriptions, and request code against shared/prompt-audit.md - prompting written for the source model is part of every migration, and it does not announce itself.
prompt-audit	Audit existing prompts, skills, and tool descriptions for dated patterns ("cruft") written for older models. Read shared/prompt-audit.md immediately and follow it in order: Step 0 (establish scope and target model from the request and the repository - state the assumptions in the report, do not stop to ask), inventory, provenance, then the pattern scan. Produce both deliverables in full - the audit report (findings with file:line, pattern, why it's obsolete for the target model, confidence) and a proposed diff - without pausing for confirmation; apply edits only if the request explicitly asked for them. Do not summarize the guide - execute it.
upgrade	Upgrade the project's Anthropic SDK dependency across a major version - currently the Python SDK, anthropic 0.x -> 1.x. Trailing words may name the language and/or a scope (upgrade python, upgrade python sdk src/). Read python/claude-api/sdk-upgrade.md immediately and follow it in order: Step 0 (confirm scope, then establish the current and target versions - a published 1.x must exist before you write a pin), the Step 1 inventory, each numbered section, then verification and the report. Do not summarize the guide - execute it. If the detected or named language has no sdk-upgrade.md in this skill, say that no major-version upgrade guide is bundled for that SDK yet and point the user at that SDK's CHANGELOG (repositories in shared/live-sources.md); do not improvise one from the Python guide. This is not model m