Building for agent use without MCP or skills

Hookdeck Inspect was developed as a webhook-testing service that coding agents can use directly through a URL without requiring MCP, skills, accounts, JavaScript execution, or setup prompts. Testing across hundreds of agent runs found that compatibility depends less on API comprehension than on the limitations of fetch tools and agent harnesses, which may lack header support, cache responses, summarize pages, block background processes, or prevent agents from sleeping or streaming events. The service therefore uses server-rendered plain-text instructions, GET-only interactions, query parameters instead of headers, unique resume URLs, no-store caching, and a blocking wait endpoint that returns either a received webhook or a timeout with a fresh URL. Embedded machine-readable metadata, streaming, guided polling, retry commands, and forceful instructions were generally less effective, while visible page copy substantially improved agent behavior but could affect models differently. The author argues that MCP can help agents access services, but it cannot resolve environmental constraints imposed by their hosting platforms, making multi-model and multi-environment testing essential. Hookdeck Inspect’s final design aims to provide a self-describing webhook URL that most non-entry-level models can use reliably, including for creating a webhook and reporting when a request arrives.

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