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 5.5, which you can access via the exact model string claude-opus-5-5. 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. When a streaming request defines user-defined (client) tools, set eager_input_streaming: true on each of those tools so large tool inputs (file contents, code, documents) stream as they are generated instead of arriving in one burst after the server finishes buffering them; the client then owns validation: the SDKs' tolerant parsers can return a silently truncated input instead of raising, so validate each parsed tool input against its schema before running it (the typed runner helpers such as betaZodTool / typed @beta_tool do this; betaTool() JSON-Schema tools and manual loops must validate themselves), treat a failure like invalid JSON (INVALID_JSON error tool_result when you hold the block, re-issue otherwise), check max_tokens / refusal stop reasons before running tools, and catch only the SDK's JSON error, never its typed API errors - pattern in shared/tool-use-concepts.md -> Eager input streaming. Leave it off for non-streaming requests, for server tools, and when the request goes through a proxy or an older Bedrock model deployment that rejects the field.

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 5.5 / Sonnet 5 / Opus 5.5 / 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 5.5/5/4.8/4.7/4.6, Sonnet 5.5, 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, tool descriptions, skills, and agent configuration files (CLAUDE.md, rule files, commands, subagents) for dated patterns ("cruft"): text written for older models, and instructions the repository has outgrown or that contradict each other. Read shared/prompt-audit.md immediately and follow it in order: Step 0 (establish scope and target model