Ollama Patterns

Quick Guide: Use the ollama npm package to run LLMs locally. Use ollama.chat() for conversations and ollama.generate() for single prompts. Enable streaming with stream: true and iterate with for await. Use format with a JSON schema (via zodToJsonSchema) for structured outputs. Use tools array for function calling. Use ollama.embed() for embeddings. Models run on your machine -- no API keys required for local use, but be aware of model loading time and memory usage.

---

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use ollama.chat() for conversations and ollama.generate() for single-prompt completions -- they have different parameter shapes)

(You MUST handle model loading delays -- the first request after a model is loaded takes significantly longer due to model initialization)

(You MUST use zodToJsonSchema() from zod-to-json-schema for structured outputs -- do NOT manually construct JSON schemas)

(You MUST accumulate streamed thinking, content, and tool_calls fields to maintain conversation history in multi-turn interactions)

(You MUST never assume a model is already pulled -- check with ollama.list() or handle errors from missing models gracefully)

</critical_requirements>

---

Auto-detection: Ollama, ollama, ollama.chat, ollama.generate, ollama.embed, ollama.pull, ollama.list, ollama.show, ollama.delete, ollama.ps, ollama.abort, ollama.create, keep_alive, zodToJsonSchema, OLLAMA_HOST, llama3, mistral, qwen, gemma, phi, deepseek, local LLM

When to use:

• Running LLMs locally for development, testing, or privacy-sensitive workloads
• Building chat applications with local models (Llama, Mistral, Qwen, Gemma, etc.)
• Extracting structured data from text or images using local models with JSON schemas
• Implementing tool calling / function calling with locally-hosted models
• Generating embeddings for RAG or semantic search without cloud API costs
• Managing local model lifecycle (pull, list, show, delete, copy)
• Prototyping AI features before committing to a cloud provider

Key patterns covered:

• Client setup (default and custom instances)
• Chat completions (ollama.chat) and text generation (ollama.generate)
• Streaming with for await and accumulated state
• Structured output with format + zodToJsonSchema
• Tool calling with tools array and multi-turn tool loops
• Vision / multimodal inputs with images parameter
• Embeddings with ollama.embed()
• Model management (pull, list, show, delete, copy, ps)
• OpenAI-compatible endpoint for drop-in migration

When NOT to use:

• Production workloads requiring guaranteed uptime and SLAs -- use a cloud LLM provider
• Multi-provider applications where you need to switch between OpenAI, Anthropic, Google -- use a unified provider SDK
• Applications requiring the latest proprietary models (GPT-5, Claude) -- those are cloud-only

---

Examples Index

• Core: Setup, Chat & Generate -- Client init, chat, generate, streaming, error handling
• Tool Calling -- Tool definitions, single/parallel calls, multi-turn agent loops
• Structured Output -- JSON schema via Zod, vision extraction
• Embeddings & Vision -- Embeddings, image analysis, multimodal
• Model Management -- Pull, list, show, delete, copy, ps
• Quick API Reference -- Method signatures, options, response types, model names

---

Philosophy

The Ollama JavaScript library is a thin client over Ollama's local REST API (default http://127.0.0.1:11434). It provides direct access to locally-running open-source LLMs with zero cloud dependencies.

Core principles:

1. Local-first -- Models run on your hardware. No API keys required for local use, complete data privacy, no per-token costs. Trade-off: you need sufficient GPU/CPU memory.
2. Simple API -- ollama.chat() and ollama.generate() are the two primary methods. The default import is a pre-configured singleton client; create custom instances with new Ollama() for non-default hosts.
3. Streaming by default in REST, opt-in in SDK -- The REST API streams by default. The SDK returns full responses by default; set stream: true to get an AsyncGenerator.
4. Model-agnostic -- The same API works with any Ollama-supported model (Llama, Mistral, Qwen, Gemma, Phi, DeepSeek, etc.). Model capabilities (vision, tool calling, structured output) depend on the model.
5. OpenAI-compatible -- Ollama exposes /v1/chat/completions and /v1/embeddings endpoints, allowing the OpenAI SDK to connect with baseURL: 'http://localhost:11434/v1'.

---

Core Patterns

Pattern 1: Client Setup

The default import is a pre-configured singleton pointing to http://127.0.0.1:11434.

// lib/ollama.ts -- default client (most common)
import ollama from "ollama";

// Use directly -- connects to localhost:11434
const response = await ollama.chat({
  model: "llama3.1",
  messages: [{ role: "user", content: "Hello" }],
});

// lib/ollama.ts -- custom client for non-default host
import { Ollama } from "ollama";

const ollama = new Ollama({
  host: "http://192.168.1.100:11434",
});

export { ollama };

Why good: Minimal setup, default client requires zero configuration, custom client for remote servers

// BAD: Hardcoding host inline everywhere
import { Ollama } from "ollama";
const response = await new Ollama({ host: "http://192.168.1.100:11434" }).chat({
  model: "llama3.1",
  messages: [{ role: "user", content: "Hello" }],
});

Why bad: Creates a new client instance per request, no reuse, host scattered across codebase

See: examples/core.md for cloud API setup, custom headers, browser usage

---

Pattern 2: Chat Completions

Multi-turn conversations with message history. You manage the messages array.

import ollama from "ollama";

const response = await ollama.chat({
  model: "llama3.1",
  messages: [
    { role: "system", content: "You are a helpful coding assistant." },
    { role: "user", content: "Explain TypeScript generics." },
  ],
});

console.log(response.message.content);

Why good: Clear message roles, system message for behavior control, direct content access

// BAD: Not checking response, no system message
const res = await ollama.chat({
  model: "llama3.1",
  messages: [{ role: "user", content: "do something" }],
});

Why bad: No system instruction means unpredictable behavior, vague prompt

See: examples/core.md for multi-turn conversations, model options

---

Pattern 3: Text Generation

Single-prompt completions without message history. Simpler than chat for one-shot tasks.

import ollama from "ollama";

const response = await ollama.generate({
  model: "llama3.1",
  prompt: "Write a haiku about TypeScript.",
  system: "You are a creative writer.",
});

console.log(response.response);

Why good: Simpler API for one-shot tasks, system parameter instead of message array

See: examples/core.md for generate with images, suffix, raw mode

---

Pattern 4: Streaming

Set stream: true to get an AsyncGenerator. Iterate with for await.

import ollama from "ollama";

const stream = await ollama.chat({
  model: "llama3.1",
  messages: [{ role: "user", content: "Explain async/await." }],
  stream: true,
});

for await (const chunk of stream) {
  process.stdout.write(chunk.message.content);
}
console.log(); // newline

Why good: Progressive output for better UX, memory-efficient for long responses

// BAD: Not consuming the stream
const stream = await ollama.chat({
  model: "llama3.1",
  messages: [{ role: "user", content: "Hello" }],
  stream: true,
});
// Stream never consumed -- response is lost

Why bad: Stream must be consumed via iteration, otherwise the response is silently lost

See: examples/core.md for generate streaming, abort, thinking mode streaming

---

Pattern 5: Structured Output with Zod

Use format with a JSON schema to constrain model output. Use zodToJsonSchema() from zod-to-json-schema to convert Zod schemas.

import ollama from "ollama";
import { z } from "zod";
import { zodToJsonSchema } from "zod-to-json-schema";

const Country = z.object({
  name: z.string(),
  capital: z.string(),
  languages: z.array(z.string()),
});

type Country = z.infer<typeof Country>;

const response = await ollama.chat({
  model: "llama3.1",
  messages: [
    {
      role: "user",
      content: "Tell me about France. Respond in JSON.",
    },
  ],
  format: zodToJsonSchema(Country),
});

const country: Country = Country.parse(JSON.parse(response.message.content));
console.log(country.capital); // "Paris"

Why good: Type-safe output via Zod, JSON schema constrains model output, parse validates response

// BAD: Using format: 'json' without a schema
const response = await ollama.chat({
  model: "llama3.1",
  messages: [{ role: "user", content: "Tell me about France as JSON" }],
  format: "json",
});
// No schema enforcement -- model can return any JSON shape

Why bad: format: 'json' only ensures valid JSON syntax, not structure -- use a JSON schema for reliable extraction

See: examples/structured-output.md for vision extraction, complex schemas

---

Pattern 6: Tool Calling

Define tools the model can request. Handle tool_calls in responses and feed results back.

import ollama from "ollama";

const tools = [
  {
    type: "function" as const,
    function: {
      name: "get_weather",
      description: "Get the current weather for a city",
      parameters: {
        type: "object",
        required: ["city"],
        properties: {
          city: { type: "string", description: "City name" },
        },
      },
    },
  },
];

const response = await ollama.chat({
  model: "llama3.1",
  messages: [{ role: "user", content: "What is the weather in Tokyo?" }],
  tools,
});

if (response.message.tool_calls?.length) {
  for (const toolCall of response.message.tool_calls) {
    console.log(`Call: ${toolCall.function.name}`);
    console.log(`Args:`, toolCall.function.arguments);
  }
}

Why good: Standard tool schema format, checks for tool_calls before processing, arguments already parsed (not stringified JSON)

See: examples/tools.md for multi-turn tool loops, streaming tool calls, parallel tools

---

Pattern 7: Embeddings

Use ollama.embed() for text embeddings. Supports single or batch inputs.

import ollama from "ollama";

const EMBEDDING_MODEL = "nomic-embed-text";

const response = await ollama.embed({
  model: EMBEDDING_MODEL,
  input: [
    "TypeScript is a typed superset of JavaScript.",
    "Rust is a systems programming language.",
  ],
});

console.log(`Vectors: ${response.embeddings.length}`);
console.log(`Dimensions: ${response.embeddings[0].length}`);

Why good: Batch multiple inputs in one call, named constant for model, returns array of number arrays

See: examples/embeddings-vision.md for semantic search, cosine similarity

---

Pattern 8: Model Management

Pull, list, show, and delete models programmatically.

import ollama from "ollama";

// List available models
const models = await ollama.list();
for (const model of models.models) {
  console.log(`${model.name} (${model.size} bytes)`);
}

// Pull a model with progress streaming
const stream = await ollama.pull({ model: "llama3.1", stream: true });
for await (const progress of stream) {
  console.log(
    `${progress.status}: ${progress.completed ?? 0}/${progress.total ?? 0}`,
  );
}

// Show model details
const info = await ollama.show({ model: "llama3.1" });
console.log(`Parameters: ${info.details.parameter_size}`);
console.log(`Quantization: ${info.details.quantization_level}`);

// Delete a model
await ollama.delete({ model: "old-model" });

Why good: Streaming progress for large downloads, programmatic model lifecycle, detailed model metadata

See: examples/model-management.md for copy, create, running models (ps)

---

Pattern 9: OpenAI-Compatible Endpoint

Ollama exposes /v1/chat/completions and /v1/embeddings that work with the OpenAI SDK.

import OpenAI from "openai";

const OLLAMA_BASE_URL = "http://localhost:11434/v1";

const client = new OpenAI({
  baseURL: OLLAMA_BASE_URL,
  apiKey: "ollama", // Required by SDK but unused by Ollama
});

const completion = await client.chat.completions.create({
  model: "llama3.1",
  messages: [{ role: "user", content: "Why is the sky blue?" }],
});

console.log(completion.choices[0].message.content);

Why good: Drop-in replacement for OpenAI SDK code, named constant for URL, easy to switch between local and cloud

When to use: When migrating existing OpenAI SDK code to local models, or when you want to use OpenAI SDK tooling (structured outputs, streaming helpers) with local models

When not to use: For new Ollama-native code, prefer the ollama package directly -- it exposes Ollama-specific features (model management, keep_alive, thinking mode) that the OpenAI compat layer does not

See: reference.md for supported and unsupported OpenAI features

---

<decision_framework>

Decision Framework

ollama.chat() vs ollama.generate()

Need multi-turn conversation history?
+-- YES -> ollama.chat() (messages array with roles)
+-- NO -> Is it a single prompt completion?
    +-- YES -> ollama.generate() (simpler API)
    +-- NO -> ollama.chat() (default choice for most use cases)

Native Ollama SDK vs OpenAI-Compatible Endpoint

Do you have existing OpenAI SDK code to migrate?
+-- YES -> Use OpenAI SDK with baseURL: 'http://localhost:11434/v1'
+-- NO -> Do you need Ollama-specific features?
    +-- YES -> Use ollama package (model management, keep_alive, thinking, abort)
    +-- NO -> Either works, prefer ollama package for new code

Structured Output vs Plain Text

Do you need structured data from the model?
+-- YES -> Use format parameter with zodToJsonSchema()
|   +-- Always include "respond in JSON" in the prompt
|   +-- Always parse and validate with Zod after receiving response
+-- NO -> Omit format parameter (plain text response)

Model Selection Guidance

What is your task?
+-- General chat / coding -> llama3.1 (8B for speed, 70B for quality)
+-- Fast + small -> phi4-mini, gemma3 (smaller memory footprint)
+-- Code generation -> qwen2.5-coder, deepseek-coder-v2
+-- Vision/multimodal -> llama3.2-vision, gemma3
+-- Embeddings -> nomic-embed-text, all-minilm
+-- Tool calling -> llama3.1, qwen3, mistral
+-- Reasoning/thinking -> qwen3 (with think: true), deepseek-r1

</decision_framework>

---

<red_flags>

RED FLAGS

High Priority Issues:

• Not handling model loading time -- first request after model load can take 30+ seconds on CPU; show a loading indicator or set keep_alive to keep models warm
• Using format: 'json' instead of a JSON schema -- only ensures valid JSON syntax, not structure; always use zodToJsonSchema() for reliable extraction
• Not accumulating streamed fields in multi-turn conversations -- you must collect thinking, content, and tool_calls from all chunks to maintain history
• Assuming all models support all features -- tool calling, vision, and structured output depend on the model; check model capabilities first

Medium Priority Issues:

• Not setting keep_alive for latency-sensitive applications -- models unload after 5 minutes of inactivity by default; set keep_alive: '30m' or keep_alive: -1 (indefinite) for persistent sessions
• Creating new Ollama() instances per request instead of reusing a singleton client
• Not handling AbortError when using ollama.abort() -- listening threads throw when streams are cancelled
• Ignoring model size vs available memory -- loading a 70B model on 8GB RAM will fail or swap heavily

Common Mistakes:

• Confusing ollama.chat() and ollama.generate() parameters -- chat uses messages[], generate uses prompt and system
• Using ollama.embeddings() (deprecated) instead of ollama.embed() -- the newer embed() method supports batch inputs
• Passing HTTP/HTTPS URLs to images parameter -- Ollama accepts file paths, Uint8Array, or base64-encoded strings, but not remote URLs
• Using tool calling with models that do not support it -- not all models handle tools; use Llama 3.1+, Qwen 3, or Mistral for reliable tool calling
• Forgetting to JSON.parse() the response content when using structured output -- Ollama returns JSON as a string in message.content, not a parsed object

Gotchas & Edge Cases:

• Ollama returns tool call arguments as already-parsed objects (not JSON strings like OpenAI) -- toolCall.function.arguments is an object, not a string
• The keep_alive parameter accepts both duration strings ('5m', '1h') and numbers (seconds) -- 0 unloads immediately, -1 keeps loaded indefinitely
• ollama.abort() cancels ALL active streams for that client instance -- for individual stream cancellation, use stream.abort() on the returned stream object
• Model names can include tags (llama3.1:8b, llama3.1:70b) -- omitting the tag uses the default (usually smallest)
• The think parameter enables extended reasoning but only works with models that support it (Qwen 3, DeepSeek R1) -- it adds a thinking field to the response alongside content
• Browser usage requires importing from ollama/browser instead of ollama -- the default import uses Node.js-specific APIs
• Cloud API access (ollama.com) requires an API key via Authorization: Bearer header and setting host: 'https://ollama.com'
• Response includes performance metrics: total_duration, eval_count, eval_duration (in nanoseconds) -- calculate tokens/second with eval_count / eval_duration * 1e9

</red_flags>

---

<critical_reminders>

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use ollama.chat() for conversations and ollama.generate() for single-prompt completions -- they have different parameter shapes)

(You MUST handle model loading delays -- the first request after a model is loaded takes significantly longer due to model initialization)

(You MUST use zodToJsonSchema() from zod-to-json-schema for structured outputs -- do NOT manually construct JSON schemas)

(You MUST accumulate streamed thinking, content, and tool_calls fields to maintain conversation history in multi-turn interactions)

(You MUST never assume a model is already pulled -- check with ollama.list() or handle errors from missing models gracefully)

Failure to follow these rules will produce unreliable, poorly-typed, or broken local LLM integrations.

</critical_reminders>