1,300 pages for code.

mid-conversation-system-messages Claude Developer Platform · in the page build-with-claude/mid-conversation-system-messages …ls` returns a 400 error (on the Claude API, with `error.details.error_code` set to `tool_reference_unresolved`). A `tool_addition` block can instead [carry the tool's full definition](https://platform… multilingual-support Claude Developer Platform · in the page build-with-claude/multilingual-support …h keeps the instruction stable across every turn of a conversation. <CodeGroup> ```bash cURL curl https://api.anthropic.com/v1/messages \ -H "content-type: application/json" \ -H "x-api-k… overview Claude Developer Platform · in the page build-with-claude/overview …| Up to 1M tokens for processing large documents, extensive code bases, and long conversations.… pdf-support Claude Developer Platform · in the page build-with-claude/pdf-support …ways: 1. As a URL reference to a PDF hosted online 2. As a base64-encoded PDF in `document` content blocks 3. By a `file_id` from the [Files API](https://platform.claude.com/docs/en/build-with-claud… preserved-thinking Claude Developer Platform · in the page build-with-claude/preserved-thinking …tegration append-only regardless of your account's age**, so the same code works on every account, including newer accounts enforced by default. ## Who needs to change anything Nothing changes for y… Request 2 caches its request content (not the response) Claude Developer Platform · in the page build-with-claude/prompt-caching …gets cached. The simplest way to start is with automatic caching: <CodeGroup> ```bash cURL curl https://api.anthropic.com/v1/messages \ -H "content-type: application/json" \ -H "x-api-k… claude-prompting-best-practices Claude Developer Platform · in the page build-with-claude/prompt-engineering/claude-prompting-best-practices …tone for your use case. Even a single sentence makes a difference: <CodeGroup> ```bash cURL curl https://api.anthropic.com/v1/messages \ -H "content-type: application/json" \ -H "x-api-k… prompting-claude-fable-5 Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-fable-5 …utput on financial analysis, spreadsheets, slides, and documents. * **Code review and debugging.** Bug-finding recall (outside the cybersecurity domains the safety classifiers cover) is noticeably hig… Delivering work Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-fable-5-1 …tool results, and a fresh turn-scoped copy of the nudge follows it. <CodeGroup exclude="shell"> ```python Python import anthropic from anthropic.types.beta import ( BetaMessageParam,… prompting-claude-haiku-5-5 Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-haiku-5-5 …ting-claude-haiku-5-5#prevent-early-stopping-in-long-agent-prompts) * Code changes are reported as done without a check that exercises them: [Tell coding agents to verify their changes](https://platfo… prompting-claude-opus-4-8 Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-opus-4-8 …t in the [frontend-design skill](https://github.com/anthropics/claude-code/blob/main/plugins/frontend-design/skills/frontend-design/SKILL.md). However, Claude Opus 4.8 generates distinctive, creative… prompting-claude-opus-5 Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-opus-5 …le-turn edits, where the difference from prior models is smaller. * **Code review and bug-finding:** Claude Opus 5 reviews code with high precision and recall: it finds real bugs at a high rate per pa… prompting-claude-opus-5-5 Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-opus-5-5 …abilities that matter most for prompting are: * **Agentic coding and code review:** The model is strongest on multistep work in a real repository, such as carrying a change through a large code base… prompting-claude-sonnet-5 Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-sonnet-5 …mpt. The [frontend-design skill](https://github.com/anthropics/claude-code/blob/main/plugins/frontend-design/skills/frontend-design/SKILL.md) provides a fuller treatment, but this snippet works well a… prompting-claude-sonnet-5-5 Claude Developer Platform · in the page build-with-claude/prompt-engineering/prompting-claude-sonnet-5-5 …rompting-claude-sonnet-5-5#mid-turn-user-messages-and-task-budgets) * Code changes are reported as done without a test or build run: [Verification on coding tasks](https://platform.claude.com/docs/en/… refusals-and-fallback Claude Developer Platform · in the page build-with-claude/refusals-and-fallback ….com/docs/en/build-with-claude/refusals-and-fallback#manual-retry). <CodeGroup> ```bash cURL curl --fail-with-body -sS https://api.anthropic.com/v1/messages \ -H "x-api-key: $ANTHROPIC_API_KE… search-results Claude Developer Platform · in the page build-with-claude/search-results …e retrieval step runs every time. ### Example: Knowledge base tool <CodeGroup exclude="shell"> <CodeGroupItem language="cURL"> The tool-calling flow needs search logic in your application, whi… skills-guide Claude Developer Platform · in the page build-with-claude/skills-guide …skills). </Note> Skills integrate with the Messages API through the [code execution tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/code-execution-tool). Whether using pre-built S… streaming Claude Developer Platform · in the page build-with-claude/streaming …c and async streams. See the documentation in each SDK for details. <CodeGroup exclude="shell:cURL"> ```bash CLI ant messages create --stream \ --model claude-opus-5-5 \ --max-tokens 1024… structured-outputs Claude Developer Platform · in the page build-with-claude/structured-outputs …lper that validates responses still enforces every constraint in your code. **Example:** A field with `minimum: 100` becomes a plain integer in the sent schema, and the SDK adds `{minimum: 100}` to t… task-budgets Claude Developer Platform · in the page build-with-claude/task-budgets …Add `task_budget` to `output_config` and include the beta header: <CodeGroup> ```bash cURL curl https://api.anthropic.com/v1/messages \ -N \ -H "x-api-key: $ANTHROPIC_API_KEY" \ -H… thinking Claude Developer Platform · in the page build-with-claude/thinking …ed"` so the thinking text is visible, and use a large `max_tokens`: <CodeGroup> ```bash cURL curl https://api.anthropic.com/v1/messages \ -H "x-api-key: $ANTHROPIC_API_KEY" \ -H "anthropi… thinking-steering-and-cost Claude Developer Platform · in the page build-with-claude/thinking-steering-and-cost …f: <Accordion title="Effort changes invalidate the prompt cache"> <CodeGroup exclude="shell:cURL, shell:CLI"> <CodeGroupItem language="cURL"> This workflow needs more logic than a single… thinking-tool-workflows Claude Developer Platform · in the page build-with-claude/thinking-tool-workflows …ing-thinking-blocks); this page shows those rules applied in runnable code. ## The rules this walkthrough applies Each link leads to the full statement on the Thinking page: * [Limit tool choice to… thinking-troubleshooting Claude Developer Platform · in the page build-with-claude/thinking-troubleshooting …d back differs from the one the API returned, most often because your code filters content blocks by type and drops `redacted_thinking` blocks, or rebuilds the assistant message instead of echoing it.… token-counting Claude Developer Platform · in the page build-with-claude/token-counting …gents-and-tools/tool-use/server-tools) such as web search, web fetch, code execution, and tool search (every server tool except the [advisor tool](https://platform.claude.com/docs/en/agents-and-tools/… vision Claude Developer Platform · in the page build-with-claude/vision …image` content blocks using one of three source types: 1. A base64-encoded image embedded in the request body 2. A URL reference to an image hosted online 3. A `file_id` returned by the [Files API](h… vision-coordinates Claude Developer Platform · in the page build-with-claude/vision-coordinates …`1000`."* Always ask for pixel coordinates and normalize in your own code if you need to. To get coordinates as machine-readable JSON instead of prose, define a schema with [structured outputs](https… working-with-messages Claude Developer Platform · in the page build-with-claude/working-with-messages …/models/opus-5-5/migration-guide#opus-46-breaking-changes). </Note> <CodeGroup> ```bash cURL #!/bin/sh curl https://api.anthropic.com/v1/messages \ -H "x-api-key: $ANTHROPIC_API_KEY" \… API usage primer for Claude Claude Developer Platform · in the page claude_api_primer …-5-20251001 ``` ## Calling the API ### Basic request and response <CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby"> ```bash CLI ant messages create \ --model claude-… apply Claude Developer Platform · in the page cli-sdks-libraries/cli/apply --- title: Manage resources as code with ant apply url: https://platform.claude.com/docs/en/cli-sdks-libraries/cli/apply description: Declare agents, environments, skills, memory stores, deployments,… On a remote host without a browser: Claude Developer Platform · in the page cli-sdks-libraries/cli/authentication …pass `--no-browser` to print the authorize URL and paste the returned code back into the terminal. ```bash CLI ant auth login # On a remote host without a browser: ant auth login --no-browser # Bin… quickstart Claude Developer Platform · in the page cli-sdks-libraries/cli/quickstart …bodies </Card> <Card title="CLI scripting and automation" icon="code" href="https://platform.claude.com/docs/en/cli-sdks-libraries/cli/scripting"> Version control for API resources, scriptin… scripting Claude Developer Platform · in the page cli-sdks-libraries/cli/scripting …, chain ant CLI commands in scripts, operate on resources from Claude Code, and authenticate curl calls with CLI credentials. --- This page covers task-oriented workflows built on the `ant` CLI. For… using Claude Developer Platform · in the page cli-sdks-libraries/cli/using …is scanned document."} ]}' ``` The CLI detects the file type and encodes binary files as base64 automatically. To force a specific encoding use `@file://` for plain text or `@data://` for base64. E… apple-foundation-models Claude Developer Platform · in the page cli-sdks-libraries/libraries/apple-foundation-models …e Foundation Models framework supports server-side language models * Xcode 27 (beta) * A Claude API key from the [Claude Console](https://platform.claude.com/) for development. See [Authentication](ht… openai-sdk Claude Developer Platform · in the page cli-sdks-libraries/libraries/openai-sdk …r that lets you use the OpenAI SDK to test the Claude API. With a few code changes, you can evaluate Anthropic model capabilities. --- <Note> This compatibility layer is primarily intended to test… middleware Claude Developer Platform · in the page cli-sdks-libraries/middleware …ude SDK provides a middleware (or interceptor) hook that lets you run code before a request is sent and after the response is received. Use middleware for cross-cutting concerns such as logging, custo… overview Claude Developer Platform · in the page cli-sdks-libraries/overview …DK surface </Card> </CardGroup> ## Building agents or using Claude Code? The CLI, client SDKs, and libraries are for calling the Claude API yourself: you send each request and handle each response… csharp Claude Developer Platform · in the page cli-sdks-libraries/sdks/csharp …lications written in C#. <Info> For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers C#-specific SDK feature… go Claude Developer Platform · in the page cli-sdks-libraries/sdks/go …lications written in Go. <Info> For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers Go-specific SDK feature… java Claude Developer Platform · in the page cli-sdks-libraries/sdks/java …asynchronous operations. <Info> For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers Java-specific SDK featu… php Claude Developer Platform · in the page cli-sdks-libraries/sdks/php …PHP 8.1.0+ application. <Info> For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers PHP-specific SDK featur… For Amazon Bedrock support Claude Developer Platform · in the page cli-sdks-libraries/sdks/python …, and Microsoft Foundry. <Info> For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers Python-specific SDK fea… Automatically handles tool execution loop Claude Developer Platform · in the page cli-sdks-libraries/sdks/ruby …e `connection_pool` gem. <Info> For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers Ruby-specific SDK featu… typescript Claude Developer Platform · in the page cli-sdks-libraries/sdks/typescript …ypeScript or JavaScript. <Info> For API feature documentation with code examples, see the [API reference](https://platform.claude.com/docs/en/api/overview). This page covers TypeScript-specific SDK… get-started Claude Developer Platform · in the page get-started …to get a URL you can open on another device, then paste the returned code back into the terminal. For non-interactive environments such as CI, see [CLI authentication options](https://platform.claude… home Claude Developer Platform · in the page home …key in Claude Console </HomeQuickChip> <HomeQuickChip icon="CodeBrackets" href="https://platform.claude.com/docs/en/api/overview"> API reference </HomeQuickChip> ```python Pyt… intro Claude Developer Platform · in the page intro …create your API key. Keep the key out of source control, client-side code, and prompts. Check whether your workload can use Workload Identity Federation instead of a static key. [Read the authen… access-transparency Claude Developer Platform · in the page manage-claude/access-transparency …ccess occurs only for safety review or incident response. See [Reason codes](https://platform.claude.com/docs/en/manage-claude/access-transparency#reason-codes). Access Transparency is available to…