Build a research agent

A research agent answers questions by searching the web, reading pages, and synthesizing a sourced summary. It's one of the most useful agent archetypes - and one of the easiest to build badly. The failure mode isn't not producing output; it's producing confident-sounding output that cites made-up sources. This guide is how to build one that actually gives you answers you can trust.

What you're building.

An agent that takes a research question and produces a 200-500 word summary with every claim citation-backed.

The architecture.

Tools you'll need

• Web search. Brave Search, Tavily, or Exa via MCP. Tavily is tuned for AI; Brave is cheap.
• Fetch URL. Pulls page content. Plain curl works; better: a service that handles rendering (Firecrawl, Jina Reader).
• Optional: academic search. If your domain needs papers (Semantic Scholar MCP, arXiv).

The prompt structure

You are a research assistant.

Goal: produce a sourced, accurate summary of the user's question.

Process:
1. Decompose the question into 2, 4 search queries (different angles)
2. Run the searches (parallel)
3. From results, pick the 3, 5 most authoritative-looking sources
4. Fetch and read those pages
5. Extract key claims with source URLs
6. Write a 200, 500 word summary that:
   - States what's known clearly
   - Surfaces disagreements between sources
   - Cites every claim with [1], [2], etc.
   - Lists full source URLs at the end

Rules:
- Never state a claim without a source
- If sources conflict, surface the conflict, don't hide it
- If you can't answer confidently, say so and explain what's missing

Stop after 5 search rounds even if you want more data.

Why the prompt is structured this way

• Decompose first. Parallel searches with diverse queries beats one big search.
• Authoritative filter. Without this instruction, the model reads whatever ranks first. Prefer .edu, .gov, reputable publications.
• Explicit stop. Without it, research agents keep searching. "More data = better answer" is wrong past a point.
• Conflict surfacing. The biggest failure mode of research agents is averaging contradictory sources into a flat-sounding consensus that didn't exist.

Tool-use patterns

Parallel searches save latency. Emit multiple tool calls in one turn:

[tool_use: search("MCP security model")]
[tool_use: search("MCP vs OAuth scopes")]
[tool_use: search("prompt injection tool output")]

Harness executes concurrently; all three results returned in the next turn.

Quality controls

Source diversity

Instruct: "Your sources must come from at least 3 different domains."

Recency check

If topic is time-sensitive: "Prefer sources from the last 12 months. If using older, flag it."

Hallucination guard

The biggest failure mode: the model produces a citation-looking output but the citations don't support the claim. Add a validation step:

After writing the summary:
- For each claim, quote the sentence from the source that supports it
- If you can't find a direct quote, remove the claim

Evaluation

Build an eval set: 20 questions with known good answers. For each:

• Does the summary cover the key points?
• Are citations real (not hallucinated URLs)?
• Do citations actually support the claims?
• Is any major viewpoint missing?

Use LLM-as-judge with a clear rubric. Score over time.

Scaling up

For serious research tasks:

• Add a planner that breaks big topics into sub-research tasks, each a sub-agent
• Cache source content, repeat research on similar topics shouldn't re-fetch
• Keep a "visited" list per session to avoid re-reading the same URL
• For domains you research often (e.g., competitors), build a knowledge base you refresh weekly

What not to do.

A good research agent's output is indistinguishable from a careful human analyst's. A bad one produces plausible-sounding prose with citations that either don't exist or don't say what they're quoted as saying. The difference is in the controls above - don't skip any of them.