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Cloudflare blocks AI bots by default, causing JSON-RPC errors

By PulseAugur Editorial · [1 sources] ·

A developer encountered an issue where their MCP server was returning HTML error messages instead of the expected JSON-RPC responses. After extensive debugging of their own code, they discovered the problem was not within their application but rather a Cloudflare managed rule that was blocking AI crawlers. This rule, enabled by default, caused requests from specific user agents, like ClaudeBot and GPTBot, to receive a 403 Forbidden response with an HTML error page, while standard tools like `curl` were unaffected. AI

IMPACT Highlights how default security settings in infrastructure can inadvertently block legitimate AI traffic, impacting service availability.

RANK_REASON Developer troubleshooting a specific technical issue with a third-party service.

Read on dev.to — MCP tag →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Cloudflare blocks AI bots by default, causing JSON-RPC errors

How we ranked this

Signal score
22 / 100
Composite score across the factors below. Higher = stronger signal that this story matters right now.
Newsworthiness bucket
Tool
Developer troubleshooting a specific technical issue with a third-party service.
Source corroboration
Single-source cluster
Only one publisher covered this so far. Single-source stories can still rank when the publisher is high-authority, but they lack cross-source corroboration.
Topics
product, infra
Editorial topic classification. Feeds into how the story surfaces on /topic/<slug> hub pages and into the per-entity coverage mix.
AI-industry relevance
High
Clearly on-topic for AI-industry coverage.
Story freshness
Breaking (< 6h)
Fresh story with cross-source coverage still developing. Ranking may shift as more sources report.

Full methodology in our editorial standards.

COVERAGE [1]

  1. dev.to — MCP tag TIER_1 English(EN) · Alexander Lukashov ·

    Our MCP server was fine. Cloudflare was returning HTML.

    <p>This is what our MCP endpoint returned to a client speaking JSON-RPC:<br /> </p> <div class="highlight js-code-highlight"> <pre class="highlight http"><code><span class="k">HTTP</span><span class="o">/</span><span class="m">2</span> <span class="m">403</span> <span class="na">…

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