Zerdly

Developer / Claude Code User Calculators

Build great Claude Code prompts, structured-output specs and agent plans — and estimate tokens and cost.

65 tools · Top 5 most used · 100% Free

This hub pairs two distinct workflows: designing better LLM prompts and agent specs (for Claude Code and similar tools), and the everyday encode/decode/format/convert utilities developers reach for while building. The tricky part is knowing which layer you need — a vague result usually means the prompt or output spec is underspecified, not that the model is wrong, so a prompt builder or structured-output spec often fixes more than fiddling with settings.

Write and refine prompts

Start with the Prompt Builder for a general task or the specialised builders for a known job (data analysis, images, email replies); use Prompt Score and Version Compare to tighten a draft or decide between two wordings before you commit.

Claude Code Prompt BuilderAI Data Analysis Prompt BuilderAI Prompt Library BuilderPrompt Score CalculatorAI Prompt Version CompareAI Image Prompt Builder

Structured output, agents and automation

Reach for the Structured Output builder when you need reliable JSON back, the Agent Spec builder when defining a multi-step agent, and the workflow simulator/risk checker before wiring an automation that touches real systems.

AI Structured Output / JSON Prompt BuilderAI Agent Spec BuilderAI Automation Workflow SimulatorAI Workflow Risk CheckerAI Model Selector Helper

Tokens, cost and context limits

Use the Token & Cost Estimator to sanity-check spend before a large run, and the Context Window & Chunk Planner when long inputs risk truncation and need splitting.

AI Token & Cost EstimatorAI Context Window & Chunk Planner

Safety and output-quality checks

Run these before trusting or shipping model output: redact sensitive data first, then screen for hallucination risk, missing citations and answer-quality gaps.

AI Privacy Redaction HelperAI Hallucination Risk CheckerAI Citation Requirements Prompt BuilderAI Answer Quality ChecklistAI Image Prompt Critique

Everyday developer utilities

The build-and-debug staples — decode a token or timestamp, test a regex or cron line, diff text, and format or convert JSON/CSV — all local and paste-and-go.

JWT DecoderRegex TesterCron Expression ParserUnix Timestamp ConverterJSON Formatter & MinifierCSV to JSON ConverterBase64 Encoder / DecoderText Diff Checker

Encoding, hashing and generators

Grab a UUID, random value or hash, or encode/decode HTML and URLs when you need a quick value or to make text safe to transport.

UUID GeneratorRandom Number GeneratorHash GeneratorHTML Encoder / DecoderURL Encoder / DecoderQR Code GeneratorBarcode Generator

Design, front-end and assets

Convert colour formats and check contrast for accessible UIs, work out rem/px and line-height for type scales, and resize, convert or compress images without uploading them.

HEX RGB HSL Colour ConverterColour Contrast Checkerrem to px CalculatorLine Height CalculatorAspect Ratio CalculatorImage ResizerImage ConverterImage Compressor

Common tasks

  • Draft and score a Claude Code prompt before running it
  • Define a strict JSON output spec or an agent plan
  • Estimate token cost and plan chunking for long inputs
  • Decode a JWT, test a regex or parse a cron expression
  • Redact data and check output for hallucination or missing citations
  • Format JSON, convert CSV, and encode or hash values locally

Top 5 Calculators for developers and Claude Code users

1

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AI Agent Spec Builder

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AI Token & Cost Estimator

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AI Data Analysis Prompt Builder

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