Streaming Citation Parsing

This guide shows how to consume streaming responses from the Agent API, extract citations as they arrive, validate source URLs, and build a fully cited output. Streaming is essential for responsive UIs and long-running searches — you can display text and sources progressively instead of waiting for the full response.

The fast-search preset is optimized for quick, citation-rich answers. The model inserts numbered references like [1], [2] in the text, and the corresponding source URLs arrive in the search_results output item. See the Agent API Presets docs for all available presets.

Prerequisites

Install the SDKs:

pip install perplexityai openai

If you don’t have an API key yet:

Get your Perplexity API Key

Navigate to the API Keys tab in the API Portal and generate a new key.

Then export your API key as an environment variable:

export PERPLEXITY_API_KEY="your-api-key"

How Streaming Citations Work

When you stream an Agent API response with a search-enabled preset, the API sends a sequence of server-sent events (SSE). The flow is:

Search results arrive first via response.reasoning.search_results events, containing URLs, titles, and snippets for each source.
Content chunks arrive incrementally as the model generates text via response.output_text.delta events.
Citation references appear in the text as numbered markers like [1], [2], mapping to the search result id field.

Your client accumulates the text, collects search results, then maps the numbered references to source URLs using the id field.

Basic Streaming with Citations

import os
from openai import OpenAI

# The OpenAI SDK supports Agent API streaming via the /v1/responses alias
client = OpenAI(
    api_key=os.environ["PERPLEXITY_API_KEY"],
    base_url="https://api.perplexity.ai/v1",
)

stream = client.responses.create(
    input="What are the latest breakthroughs in quantum computing?",
    stream=True,
    extra_body={"preset": "fast-search"},
)

full_content = ""
search_results = []

for event in stream:
    event_type = event.type

    # Collect search results (arrive before text)
    if event_type == "response.reasoning.search_results":
        search_results = event.results

    # Accumulate content from each delta
    if event_type == "response.output_text.delta":
        full_content += event.delta
        print(event.delta, end="", flush=True)

print("\n\n--- Citations ---")
for result in search_results:
    print(f"[{result['id']}] {result['title']} — {result['url']}")

Parsing Citation References from Text

The model inserts numbered references like [1], [2] into the generated text. To build a rich output with clickable links, parse these references and map them to source URLs using the search results.

import re
from perplexity import Perplexity

client = Perplexity()


def extract_citation_refs(text: str) -> list[int]:
    """Extract all citation reference numbers from text, e.g. [1], [2]."""
    return sorted(set(int(m) for m in re.findall(r"\[(\d+)\]", text)))


def build_cited_output(content: str, search_results: list) -> str:
    """Replace [N] references with markdown links and append a references section."""
    cited_content = content

    # Build a map from id to URL
    url_map = {r.id: r.url for r in search_results}
    title_map = {r.id: r.title for r in search_results}

    # Replace inline references with markdown links
    for ref_id, url in url_map.items():
        cited_content = cited_content.replace(
            f"[{ref_id}]",
            f"[[{ref_id}]]({url})"
        )

    # Append a references section with all cited sources
    used_refs = extract_citation_refs(content)
    if used_refs:
        cited_content += "\n\n---\n**References:**\n"
        for ref in used_refs:
            if ref in url_map:
                cited_content += f"- [{ref}] {title_map[ref]} — {url_map[ref]}\n"

    return cited_content


# Non-streaming request to get content + search results
response = client.responses.create(
    preset="fast-search",
    input="What is CRISPR gene editing and how does it work?",
)

# Extract search results from the response output
content = response.output_text
search_results = []
for item in response.output:
    if item.type == "search_results":
        search_results = item.results
        break

# Build the final output with linked citations
output = build_cited_output(content, search_results)
print(output)

Validating Citation URLs

In production systems, you should validate that citation URLs are well-formed and reachable before presenting them to users. This avoids broken links and improves trust in the output.

import asyncio
import aiohttp
from urllib.parse import urlparse


def is_valid_url(url: str) -> bool:
    """Check that a URL has a valid structure."""
    try:
        result = urlparse(url)
        return all([result.scheme in ("http", "https"), result.netloc])
    except Exception:
        return False


async def check_url_reachable(url: str, timeout: float = 5.0) -> dict:
    """HEAD-request a URL to check if it's reachable."""
    if not is_valid_url(url):
        return {"url": url, "valid": False, "reason": "malformed URL"}

    try:
        async with aiohttp.ClientSession() as session:
            async with session.head(url, timeout=aiohttp.ClientTimeout(total=timeout), allow_redirects=True) as resp:
                return {
                    "url": url,
                    "valid": resp.status < 400,
                    "status": resp.status,
                }
    except asyncio.TimeoutError:
        return {"url": url, "valid": False, "reason": "timeout"}
    except Exception as e:
        return {"url": url, "valid": False, "reason": str(e)}


async def validate_citations(search_results: list) -> list[dict]:
    """Validate all citation URLs from search results concurrently."""
    tasks = [check_url_reachable(r.url) for r in search_results]
    return await asyncio.gather(*tasks)


# Usage after getting a response:
# results = asyncio.run(validate_citations(search_results))
# for r in results:
#     status = "OK" if r["valid"] else f"FAILED ({r.get('reason', r.get('status'))})"
#     print(f"  {r['url']}: {status}")

Never ask the model to generate source URLs. Always use the search_results output from the API response. Model-generated URLs can be hallucinated. The search results contain verified URLs from real web searches.

Progressive Display with Live Citation Count

For chat UIs, it’s useful to show a live citation counter as text streams in, then render the full reference list once the stream completes.

import os
import re
import sys
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["PERPLEXITY_API_KEY"],
    base_url="https://api.perplexity.ai/v1",
)


def stream_with_progress(query: str):
    """Stream a response with a live citation counter."""
    stream = client.responses.create(
        input=query,
        stream=True,
        extra_body={"preset": "fast-search"},
    )

    full_content = ""
    search_results = []
    seen_refs = set()

    for event in stream:
        if event.type == "response.reasoning.search_results":
            search_results = event.results

        if event.type == "response.output_text.delta":
            full_content += event.delta
            sys.stdout.write(event.delta)
            sys.stdout.flush()

            # Track new citation references against accumulated text
            # (individual deltas may split [N] across chunks)
            current_refs = set(int(m) for m in re.findall(r"\[(\d+)\]", full_content))
            if current_refs - seen_refs:
                seen_refs = current_refs
                sys.stdout.write(f" [📚 {len(seen_refs)} sources]")
                sys.stdout.flush()

    # Final summary
    print(f"\n\n{'='*60}")
    print(f"Response complete: {len(search_results)} sources found, {len(seen_refs)} cited")
    print(f"{'='*60}")

    # Build URL map from search results
    url_map = {r["id"]: r for r in search_results}
    for ref_id in sorted(seen_refs):
        if ref_id in url_map:
            r = url_map[ref_id]
            print(f"  ✓ [{ref_id}] {r['title']} — {r['url']}")

    return full_content, search_results


content, results = stream_with_progress(
    "What are the environmental impacts of lithium mining?"
)

Handling Search Results

The Agent API returns a search_results output item with rich metadata (id, title, snippet, URL, date) for each source. This is richer than a flat URL list — use it to build source cards, sidebars, or detailed reference sections.

from perplexity import Perplexity

client = Perplexity()

# Non-streaming request to show the full response structure
response = client.responses.create(
    preset="fast-search",
    input="What is the current state of fusion energy research?",
)

content = response.output_text

# Extract search results from the output
search_results = []
for item in response.output:
    if item.type == "search_results":
        search_results = item.results
        break

print("--- Answer ---")
print(content)

print("\n--- Search Results (rich metadata) ---")
for result in search_results:
    print(f"  [{result.id}] {result.title}")
    print(f"      URL:  {result.url}")
    print(f"      Date: {result.date}")
    print(f"      Snippet: {result.snippet[:100]}...")
    print()

Each search result includes id, title, url, snippet, and date. The id maps directly to the [N] references in the text. Use this to build rich source cards for your UI.

Complete Example: Streaming Research Assistant

A self-contained script that streams an Agent API response, extracts citations, validates URLs, and produces a formatted markdown output.

import os
import re
from urllib.parse import urlparse
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["PERPLEXITY_API_KEY"],
    base_url="https://api.perplexity.ai/v1",
)


def is_valid_url(url: str) -> bool:
    try:
        result = urlparse(url)
        return all([result.scheme in ("http", "https"), result.netloc])
    except Exception:
        return False


def stream_and_collect(query: str) -> tuple[str, list[dict]]:
    """Stream an Agent API response and return the full content and search results."""
    stream = client.responses.create(
        input=query,
        stream=True,
        extra_body={"preset": "fast-search"},
    )

    content = ""
    search_results = []

    for event in stream:
        if event.type == "response.reasoning.search_results":
            search_results = event.results

        if event.type == "response.output_text.delta":
            content += event.delta
            print(event.delta, end="", flush=True)

    print()  # newline after streaming
    return content, search_results


def format_markdown_report(query: str, content: str, search_results: list[dict]) -> str:
    """Build a markdown report with inline citation links."""
    # Build URL map from search results
    url_map = {r["id"]: r["url"] for r in search_results}
    title_map = {r["id"]: r["title"] for r in search_results}

    # Replace [N] with markdown links
    formatted = content
    for ref_id, url in url_map.items():
        if is_valid_url(url):
            formatted = formatted.replace(f"[{ref_id}]", f"[\\[{ref_id}\\]]({url})")

    # Build the report
    report = f"# {query}\n\n{formatted}\n\n"

    # Append sources
    used_refs = sorted(set(int(m) for m in re.findall(r"\[(\d+)\]", content)))
    if search_results:
        report += "## Sources\n\n"
        for result in search_results:
            marker = "→" if result["id"] in used_refs else " "
            report += f"{marker} **[{result['id']}]** {result['title']} — {result['url']}\n\n"

    return report


if __name__ == "__main__":
    query = "What are the most promising approaches to carbon capture technology?"

    print(f"Researching: {query}\n")
    print("-" * 60)

    content, search_results = stream_and_collect(query)

    print(f"\n{'=' * 60}")
    print(f"Collected {len(search_results)} sources\n")

    # Filter out any malformed URLs
    valid_results = [r for r in search_results if is_valid_url(r["url"])]
    invalid_count = len(search_results) - len(valid_results)
    if invalid_count:
        print(f"Warning: {invalid_count} sources had malformed URLs and were excluded.\n")

    report = format_markdown_report(query, content, valid_results)
    print(report)

Tips and Best Practices

Use a search-enabled preset like fast-search or pro-search for citation-rich responses. Different presets use different citation formats — fast-search uses [1], while pro-search uses [web:1].
Collect search results before processing text. During streaming, response.reasoning.search_results events arrive before text deltas. Buffer them so you have the URL map ready when citations appear.
Use the id field to map citations. Each search result has a numeric id that corresponds to the [N] reference in the text.
Validate URLs before displaying them. Use HEAD requests with timeouts to filter out any unreachable sources.
Never generate your own URLs. Use only the search_results from the API response. Model-generated URLs can be hallucinated.
Handle missing references gracefully. If a [N] reference in the text exceeds the number of search results, display the reference number without a link rather than crashing.
Consider rate limiting for URL validation. If the response includes many sources, validate them with concurrency limits to avoid overwhelming target servers.

Next Steps

Agent API Presets

Explore all presets and their citation formats.

Agent API Quickstart

Get started with the Agent API for multi-provider access and tools.

Agent API Streaming

Streaming patterns and event types for the Agent API.

​Prerequisites

Get your Perplexity API Key

​How Streaming Citations Work

​Basic Streaming with Citations

​Parsing Citation References from Text

​Validating Citation URLs

​Progressive Display with Live Citation Count

​Handling Search Results

​Complete Example: Streaming Research Assistant

​Tips and Best Practices

​Next Steps

Agent API Presets

Agent API Quickstart

Agent API Streaming

Prerequisites

How Streaming Citations Work

Basic Streaming with Citations

Parsing Citation References from Text

Validating Citation URLs

Progressive Display with Live Citation Count

Handling Search Results

Complete Example: Streaming Research Assistant

Tips and Best Practices

Next Steps