Skip to content
PromptForge
Start free

14 tools · one toolbox

The prompt toolbox for AI engineers, software engineers and vibecoders.

PromptForge puts 14 tools in one place for developers who build with AI: a system prompt maker, prompt optimizer, Cursor rules generator, image-to-prompt, MCP tools explorer, regex, JSON and encoding utilities, plus a workspace where every prompt is versioned and tested.

Open the toolbox free See pricing
  • Use the tools without an account. Sign in, free, to save your work.
  • 14 tools in one place, 5 of them AI-powered.
  • Presets and a workspace keep your best prompts reusable.
System Prompt Maker turning a one-line agent idea into a structured XML system prompt with Claude Haiku 5.5
System Prompt Maker: a one-line agent idea turned into a structured XML system prompt, with rigor, verbosity and model settings. Real product screen.

Why prompts need tooling

A prompt nobody tested is a bug nobody has found yet.

Prompts grow by copy and paste: a vague rule here, an untrusted variable pasted straight into instructions there, no output format, no tests. They work in the demo and fail on the first odd input. Treating them like code, with a linter, hardening and assertions, catches that before your users do.

91.5%

of 200+ vibe-coded apps assessed in Q1 2026 had at least one vulnerability traceable to AI hallucination.

Source: Keyhole Software, Vibe Coding Trends 2026

From an idea to a tested prompt

  1. 01

    Generate

    Describe the agent in a sentence. The System Prompt Maker returns a structured XML system prompt you can tune for rigor and verbosity.

  2. 02

    Lint

    Catch injection-unsafe templating, leaked keys, conflicting rules, vague wording and missing output formats, line by line.

  3. 03

    Harden

    Add an instruction hierarchy, delimiters around untrusted input and refusal limits, then review the diff before accepting.

  4. 04

    Test and save

    Pin assertions to test cases, compare models in the matrix, and save the prompt to your workspace with history.

Every tool a prompt passes through, on one screen

Generators, refiners and quality checks sit next to the everyday string utilities you would otherwise open five tabs for.

System Prompt Maker

From one sentence to a production-grade system prompt

Describe what the agent should do and what it must never do. PromptForge drafts role, scope, procedure and output rules in a structured format you can save as a preset.

  • Rigor, verbosity and tool-use controls
  • Choose the model that writes it
  • Save to the workspace, download or copy
PromptForge System Prompt Maker turning a one-line idea into an XML system prompt

Prompt linterPro

A linter that knows what makes prompts fail

Deterministic checks for injection safety, secrets, conflicts, structure and vague wording, each with the line number, why it matters and a one-click fix.

  • Score out of 100 with errors, warnings and notes
  • Apply all safe fixes at once
  • One-click hardening with a side-by-side diff
The prompt linter with a score, warnings and one-click safe fixes

The toolbox

The utilities you reach for every day

Prompt optimizer, image-to-prompt, Cursor rules, MCP tools explorer, text refiner and inspector, regex find and replace, case and slug converters, JSON formatter, encoders and escapers.

  • Prompt engineering, text, converter and encoder tools
  • Reusable presets for the AI tools
  • Search across every tool from the sidebar
The PromptForge tool grid: prompt engineering, text, converter and encoder tools

For the people who write the words the model runs on

Prompt engineers iterate, small teams share what works, and everyone keeps a record of why a prompt looks the way it does.

A prompt engineer experiments at a clean desk with a mechanical keyboard
Prompt engineers iterate on a system prompt and lint it before every commit.
A small startup team laughs around their laptops as one of them shows a result
Small teams share presets and tested prompts instead of chat screenshots.
A developer types on a keyboard next to a notebook of hand-drawn flow diagrams
Sketch the flow on paper, then turn it into a structured prompt in one step.

Photos are AI-generated illustrations, not customers.

The toolbox fits in your pocket

Every tool works on a phone, from the optimizer to the JSON formatter, with the same presets you saved on desktop.

The PromptForge Prompt Optimizer on a phone

a DevSpeak Labs product

One plan, four apps.

PromptForge is one of four DevSpeak Utilities apps for the inputs to AI agents: specs, system prompts, technical text and prompt tests. Each app is free to use, and one Utilities Pro plan ($5.99/month or $59.99/year) unlocks Pro in all four.

  • PromptForge's tool directory: prompt-engineering tools such as System Prompt Maker, Prompt Optimizer and Image to Prompt

    PromptForge

    Prompt engineering toolbox

    You are here

    A prompt-engineering toolbox: generators, a linter, tests and a workspace.

    Pro adds in PromptForge

    • Prompt linter
    • One-click prompt hardening
    • Assertion-based prompt tests
  • SpecStudio's Studio: a travel-booking request with allowed domains, constraints and success criteria, ready to compile into a spec

    SpecStudio

    Agent task specs

    Turn a rough request into a safety-gated spec a browser agent can follow.

    Pro adds in SpecStudio

    • Spec risk audit (OWASP LLM Top 10)
    • Export to AGENTS.md, CLAUDE.md and Cursor rules
    • Live page grounding
    • Pro template pack
    Open SpecStudio
  • Prompt Guardian's refinement dashboard: a support-agent system prompt in the editor with a clean static scan

    Prompt Guardian

    Gated prompt governance

    Attack, score and gate every system prompt change before it ships.

    Pro adds in Prompt Guardian

    • Advanced attack packs
    • OWASP LLM Top 10 (2025) report
    • Regression guard for CI
    Open Prompt Guardian
  • Dev Text Forge's workbench: an informal note about a deploy script in the source pane, next to the optimized output pane and quality gates

    Dev Text Forge

    Dev text optimizer

    Rewrite developer text into clear technical English that keeps every token.

    Pro adds in Dev Text Forge

    • Agent context mode
    • Token diet report
    • Batch optimize
    Open Dev Text Forge

Free to start. One price for Pro everywhere.

Use PromptForge free for as long as you like. When you want the Pro features, one plan covers all four utilities.

Prices in USD, taxes included. One plan for all four apps.

Free

Everything PromptForge does today. No card, no trial clock.

$0forever

Sign in with Google or email.

  • All 14 tools, including the 5 AI tools
  • System Prompt Maker and Prompt Optimizer
  • Workspace with documents, templates and presets
  • Test suites and the model matrix
  • Text, converter and encoder utilities
Start free
Recommended

Utilities Pro Pro

Pro features in PromptForge and in the other three utilities.

$5.00per month

Billed $59.99 once a year. Save 17% versus monthly.

7-day Pro trial, no card required

Sign in with Google and it starts by itself: every Pro feature in all four apps, with up to 30 Pro actions a day (100 in total) and 3 premium-model runs a day (5 in total). Then you're back on Free automatically; nothing to cancel.

One trial per email. Not available to emails that already had Utilities Pro, and new trials are limited each day.

  • Everything in Free
  • Prompt linter
  • One-click prompt hardening
  • Assertion-based prompt tests
  • Premium models
  • Pro editor: AI assist, cloud history, HTML/PDF export, token budget

Pro in all four apps

  • PromptForgeThis app
  • SpecStudioAgent task specs
  • Prompt GuardianGated prompt governance
  • Dev Text ForgeDev text optimizer
Free and Utilities Pro compared, app by app
FeatureFreePro
In PromptForge
All 14 tools, including the 5 AI tools
System Prompt Maker and Prompt Optimizer
Workspace with documents, templates and presets
Test suites and the model matrix
Text, converter and encoder utilities
Prompt linterCatch injection-unsafe templating, leaked API keys, conflicting rules, vague wording and missing output formats, with line numbers and one-click fixes.
One-click prompt hardeningAdd an instruction hierarchy, delimiters around untrusted input, and refusal and tool-use limits to a system prompt, then review the side-by-side diff before accepting.
Assertion-based prompt testsPin contains, not-contains, regex, max length, valid JSON and JSON-keys assertions to each test case and get a pass/fail table on every run.
Premium modelsThe large models in every model picker: Claude Opus 5.5, Claude Sonnet 5.5, Mistral Large 4 and Mistral Medium 3.5. Claude Haiku 5.5 (the default), Mistral Medium 3.1, Devstral 2, DeepSeek and the other fast models stay free for everyone.
Pro editor (every app)
AI writing assist in the editorRewrite, tighten, fix, expand or turn any selection into a checklist.
Cloud version historyNamed snapshots kept in the cloud, with a side-by-side diff and one-click restore.
HTML and PDF exportShare polished prompt specs with people who never open a Markdown file.
Token and context budgetSee how much of each model's context window a prompt uses before you ship it.
In SpecStudio
SpecStudio: everything free todayTurn a rough request into a safety-gated spec a browser agent can follow.
Spec risk audit (OWASP LLM Top 10)
Export to AGENTS.md, CLAUDE.md and Cursor rules
Live page grounding
Pro template pack
In Prompt Guardian
Prompt Guardian: everything free todayAttack, score and gate every system prompt change before it ships.
Advanced attack packs
OWASP LLM Top 10 (2025) report
Regression guard for CI
In Dev Text Forge
Dev Text Forge: everything free todayRewrite developer text into clear technical English that keeps every token.
Agent context mode
Token diet report
Batch optimize
  • Free stays free. Pro only adds; nothing you use today moves behind the paywall.
  • Cancel anytime from Settings → Billing. Pro stays active until the end of the period you paid for.
  • One subscription, four apps. In another app, sign in with Google using the same email and Pro is already on.
  • Secure checkout by Dodo Payments, merchant of record. It handles sales tax and VAT; prices include them.

Questions, answered

Do I need an account?

Not to use the tools. Sign in, free, to save prompts to your workspace and sync them across devices. Google sign-in takes one click; email works too.

Is the free plan really free?

Yes. Every tool, the workspace, presets, test suites and the model matrix are free with no card and no trial period.

What does Utilities Pro add here?

The prompt linter, one-click prompt hardening, assertion-based prompt tests, the Pro editor tools, and the premium models (Claude Sonnet 5.5, Claude Opus 5.5, Mistral Large 4 and Mistral Medium 3.5) in every model picker. The same plan unlocks Pro in the other three utilities.

Which models power the AI tools?

Claude Haiku 5.5 by default, with Mistral Medium 3.1 via OpenRouter as the fallback, and other models selectable per tool. Free: Claude Haiku 5.5, Mistral Medium 3.1, Devstral 2, and DeepSeek, Xiaomi MiMo and Zhipu GLM, which run only when you pick one and are processed in China. Utilities Pro adds Claude Sonnet 5.5, Claude Opus 5.5, Mistral Large 4 and Mistral Medium 3.5.

Is my prompt text used for anything else?

Prompts are sent to the model provider only to run the tool you chose. The privacy policy lists every processor and what is stored.

Can I cancel Utilities Pro?

Anytime, from Settings → Billing. You keep Pro until the end of the period you paid for, then the free plan continues.

Stop shipping prompts nobody tested.

Open the toolbox free. Upgrade for the linter, hardening and assertion tests, in this app and the other three.

Open the toolbox