Documented steps

Add to the /api/v1/chat/completions body: tools: [{"type": "openrouter:web_search"}] — the model then decides when/if to search (0 to N searches per request).
Optional tool fields: engine ("auto" default | "native" | "exa" | "firecrawl" | "parallel"), max_results (1–25, default 5), max_total_results (cap across all searches in agentic loops), search_context_size ("low" | "medium" default | "high", for native provider search), allowed_domains / excluded_domains (arrays).
engine "native" uses the provider's own search (available for Anthropic, Google, OpenAI, Perplexity, xAI); "auto" picks for you.
Pricing: Exa and Parallel cost $4 per 1,000 results from your OpenRouter credits (a default 5-result search ≈ $0.02); Firecrawl bills your own Firecrawl account credits; native search pricing varies by provider and search_context_size.
The OLD mechanisms — plugins: [{"id": "web"}] and the :online model suffix — are DEPRECATED in favor of this server tool.
Docs: https://openrouter.ai/docs/guides/features/server-tools/web-search

Known gotchas

Migrating matters behaviorally: the legacy web plugin ALWAYS searched exactly once; the server tool lets the model search zero or many times — set max_total_results to bound cost in loops.
Search results are billed per RESULT ($4/1k for Exa/Parallel), so max_results=25 quintuples the search cost vs the default 5.
Domain filtering support varies by engine — verify allowed_domains/excluded_domains behave on your chosen engine before relying on them.
If you still use :online or the web plugin, plan migration now — they are documented as deprecated.

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Use tool / function calling with OpenRouter, including the full agentic loop

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Give an OpenRouter model web search ability with the openrouter:web_search server tool

Documented steps

Known gotchas

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