Prompt Assay vs SpacePrompts

Prompt Assay is a web and API workbench for authoring, refining, versioning, testing, and shipping LLM prompts and Agent Skills. Its critique feature evaluates clarity, completeness, structure, technique use, robustness, and efficiency, with written reasons. An in-editor AI pair can brainstorm, critique, improve, rewrite, compare, and convert content. Connect your own Anthropic, OpenAI, or Google models to run a prompt across 2–5 models in parallel and compare outputs, latency, token use, and cost; optional LLM-as-Judge scoring is available. For Agent Skills, users can create multi-file bundles, critique them, and run Behavioral Evals across Claude, GPT, and Gemini. Imports accept Markdown, Anthropic JSON, OpenAI JSON, or raw text; its bundle preserves versions, tags, fragments, and metadata. The Free plan is free, with 250 calls monthly and one seat; seven initial platform-funded calls are available before BYOK is needed for ongoing use. Solo costs $49 a month and includes API and TypeScript SDK access. The public API and SDK require Solo or higher.

SpacePrompts is a prompt management platform for people and teams working with AI. It runs on the web, through an API, and with Chrome, Edge, and Firefox extensions. Users can save, organize, run, version, and reuse prompts. The Playground combines an editor, variables, model selection, and immediate runs. An Evaluator scores prompts, highlights weak areas, and gives improvement guidance. Every save creates a version that can be restored later. The prompt manager extension can turn highlighted webpage text into a prompt. Its token counter supports OpenAI, Claude, Gemini, and DeepSeek models, showing token counts and estimated costs. Pro and Team plans provide API access, limited to 60 requests per minute per key. Team workspaces add shared libraries, collaborative editing, and role permissions for up to five members. Free includes 50 prompts and daily usage limits; Pro is $5 a month billed annually, and Team is $9 a month billed annually.