Can I pre-fill form values per recipient?

Yes. Pass a recipients array with prefill objects when creating a form or adding recipients. Prefilled values appear as defaults that the user can change.

Human-in-the-Loop
for AI Agents

Free API — No Credit Card

Your AI agent creates a form via API — one recipient for a quick approval, or thousands for a company-wide survey. Each person gets a unique URL that you send through your own channels: email, Slack, or embedded on your site. When they respond, your agent gets structured JSON back.

Get Started Download Skill How It Works

The Loop

Your agent starts it. A human completes it. Your agent continues.

human-in-the-loop.txt

    ┌─────────────┐
    │   AI Agent  │  "I need human input"
    └──────┬──────┘
           │
     1. POST /api/v1/forms
           │
           ▼
    ┌───────────────┐
    │ Let's Clarify │  Generates unique URLs
    └──────┬────────┘
           │
     2. Share URL  ───►  email / slack / embed
           │
           ▼
    ┌─────────────┐
    │    Human    │  Fills out form in browser
    └──────┬──────┘
           │
     3. Submits response
           │
           ▼
    ┌───────────────┐
    │ Let's Clarify │  Stores structured JSON
    └──────┬────────┘
           │
     4. Webhook / GET results
           │
           ▼
    ┌─────────────┐
    │   AI Agent  │  Continues workflow ✓
    └─────────────┘

7

Field Types

10K

Recipients / Form

10 MB

File Upload Limit

365 d

Max Retention

Three Steps. Structured Data.

No SDKs, no frontend to build. Only HTTP and an API key.

01

Create a Form

POST your schema and context to the API. Get back a form token and unique URLs for each recipient.

02

Share the URL

Distribute the unique URL via email, Slack, WhatsApp — any channel. Each recipient gets their own link.

03

Get Structured JSON

Poll the results endpoint or receive a webhook. Every response matches your schema exactly.

See It in Action

One API call. One form. Structured JSON back.

Your AI agent is organizing the team offsite. It has already booked the venue, sent calendar invites, and arranged transport. But it doesn't know everyone's food preferences — and it can't guess those. So it creates a form via one API call, sends each person a unique link, and gets structured JSON back with exactly the data it needs to place the catering order.

Get Your API Key

curl — Register

curl -X POST https://letsclarify.ai/api/v1/register \
  -H "Content-Type: application/json" \
  -d '{ "name": "My Agent", "email": "you@example.com" }'

Response — 201 Created

{
  "api_key": "lc_...",
  "warning": "Store securely. Shown only once."
}

No credit card. No account dashboard. Just an API key.

curl — Create Form

curl -X POST https://letsclarify.ai/api/v1/forms \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer lc_..." \
  -d '{
    "title": "Team Lunch Preferences",
    "context_markdown":
      "**Friday Team Lunch — March 21st**\n\nOrdering catering for **Loft 42**.\nShare your preferences by Wednesday.",
    "recipient_count": 12,
    "retention_days": 3,
    "webhook_url": "https://your-agent.ai/hook",
    "schema": [
      { "id": "name", "type": "text",
        "label": "Your name", "required": true },
      { "id": "cuisine", "type": "select",
        "label": "Preferred cuisine",
        "required": true,
        "options": [
          { "value": "italian", "label": "Italian" },
          { "value": "japanese", "label": "Japanese" },
          { "value": "mexican", "label": "Mexican" },
          { "value": "indian", "label": "Indian" }
        ] },
      { "id": "restrictions",
        "type": "checkbox_group",
        "label": "Dietary restrictions",
        "options": [
          { "value": "vegetarian", "label": "Vegetarian" },
          { "value": "vegan", "label": "Vegan" },
          { "value": "gluten_free", "label": "Gluten-free" },
          { "value": "halal", "label": "Halal" }
        ] }
    ]
  }'

Response — 201 Created

{
  "form_token": "BVyzfoQB8IqZvt1OfUI-3fM9iGg3xdTnDutienigIPk",
  "delete_token": "NGgulTYu-sCtwll53a8o2hcQjwV3dVIFGr7ctfpuPOU",
  "base_url_template":
    "https://letsclarify.ai/f/BVyzfoQB8IqZ.../{recipient_uuid}",
  "poll_url":
    "https://letsclarify.ai/api/v1/forms/BVyzfoQB8IqZ.../results",
  "summary_url":
    "https://letsclarify.ai/api/v1/forms/BVyzfoQB8IqZ.../summary",
  "delete_url":
    "https://letsclarify.ai/api/v1/forms/BVyzfoQB8IqZ...",
  "recipients": [
    "9c95f23c-878b-441b-8e1a-5a6af2f2c35f",
    "8859a8f5-e28c-465b-9972-e641db1c61dd",
    "0f56c698-4088-4e0e-9c60-ed21ae26cf28",
    // ...12 unique UUIDs total
  ]
}

What the human sees

Team Lunch Preferences

Friday Team Lunch — March 21st

We're ordering catering for the offsite at Loft 42. Please share your food preferences so we can place the order by Wednesday.

response_json — Live Preview

{
  "name": "",
  "cuisine": "",
  "restrictions": []
}

What Your Server Receives

When a human submits, Let's Clarify POSTs structured JSON to your webhook URL.

POST https://your-agent.ai/hook

{
  "form_token": "BVyzfoQB8IqZvt1O...",
  "recipient_uuid": "9c95f23c-878b-...",
  "submitted_at": "2025-03-19T14:32:07Z",
  "response_json": {
    "name": "Alice Chen",
    "cuisine": "japanese",
    "restrictions": ["vegetarian"]
  }
}

Retries with exponential backoff. SSRF protection via DNS validation. HTTPS required.

Supported types: text, textarea, checkbox, checkbox_group, radio, select, file

Or Embed It

Drop forms into any page. The widget handles rendering, validation, file uploads, and submission. No extra CSS needed.

index.html — Embed Widget

<script src="https://letsclarify.ai/embed.js"></script>
<div data-letsclarify-form="{token}"
     data-letsclarify-recipient="{uuid}"></div>

Two lines. That's the entire integration. Works in any HTML page, React, Vue, or plain static sites.

Install the Skill

Give your AI agent the ability to collect human input — one command.

terminal

claude install github:heisee/LetsClarify-Skill

View on GitHub Download SKILL.md

Works with Claude Code, or any agent that supports skill files.

Everything Your Agent Needs

One API. All the capabilities. Zero frontend work.

File Uploads

Up to 10 files, 10 MB each. MIME detection via magic bytes.

Webhooks

Auto-POST on submission. Retry with backoff. SSRF-safe.

Field Validation

Regex, min/max length, required, min/max items.

Cursor Pagination

Stable cursors. Filter by status or updated_since.

Theme Colors

Custom hex color per form. Widget adapts automatically.

Markdown Context

Rich context above form fields. Headers, lists, code.

Batch Recipients

Up to 10,000 unique URLs per form. Add more via API.

Auto-Expiration

1-365 days retention. Data and files auto-delete.

Resubmission

Recipients can update. Latest submission wins.

7 Field Types

text, textarea, select, radio, checkbox, checkbox_group, file.

Embed Widget

Drop-in JS. No build step. Handles everything.

Prefilled Values

Pre-populate fields per recipient. Client-provided UUIDs supported.

Delete on Demand

Delete with token. All data permanently removed.

Works With Any Agent

Pure HTTP. No SDK required. Here's a form in three languages.

agent.py

import requests

resp = requests.post(
    "https://letsclarify.ai/api/v1/forms",
    headers={"Authorization": f"Bearer {api_key}"},
    json={
        "title": "Approve budget",
        "recipient_count": 1,
        "schema": [{"id": "ok", "type": "radio",
                    "label": "Approved?",
                    "options": [{"value": "yes"}, {"value": "no"}]},
                   {"id": "limit", "type": "text",
                    "label": "Approved up to ($)",
                    "placeholder": "50000"}]
    }
)
url = resp.json()["base_url_template"]

agent.js

const resp = await fetch("https://letsclarify.ai/api/v1/forms", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "Authorization": `Bearer ${apiKey}`
  },
  body: JSON.stringify({
    title: "Approve budget",
    recipient_count: 1,
    schema: [{ id: "ok", type: "radio",
               label: "Approved?",
               options: [{ value: "yes" }, { value: "no" }] },
             { id: "limit", type: "text",
               label: "Approved up to ($)",
               placeholder: "50000" }]
  })
});
const { base_url_template } = await resp.json();

terminal

curl -X POST https://letsclarify.ai/api/v1/forms \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "title": "Approve budget",
    "recipient_count": 1,
    "schema": [{
      "id": "ok", "type": "radio",
      "label": "Approved?",
      "options": [{"value": "yes"}, {"value": "no"}]
    }, {
      "id": "limit", "type": "text",
      "label": "Approved up to ($)",
      "placeholder": "50000"
    }]
  }'

Built for AI Workflows

Whenever your agent needs a human in the loop.

Approval Workflows

Get human sign-off on AI-generated proposals, budgets, or plans before executing.

Data Collection

Collect structured information from people who don't have API access or developer tools.

Human Verification

Verify AI outputs with human judgment before committing irreversible actions.

Decision Points

Let humans choose between options your agent has generated, with full context.

Document Review

Present documents for review and collect structured feedback with ratings.

Consent & Agreement

Collect explicit consent or agreement on terms before proceeding in a workflow.

Security by Design

No tracking. Data deleted automatically.

HTTPS Only

All traffic encrypted. Webhook URLs must be HTTPS.

Auto-Deletion

All data deleted after retention period. No indefinite storage.

GDPR Compliant

Data minimization. No marketing. No profiling. No cookies.

No Tracking

No analytics. No fingerprinting. No third-party scripts.

Open. Fair. Rate-Limited.

No credit card. No subscription. Register once and go.

Endpoint	Limit	Window
`POST /api/v1/register`	3 requests	1 hour
`POST /api/v1/forms`	10 requests	1 minute
`GET /api/v1/forms/*`	60 requests	1 minute
`GET /api/v1/embed/*`	30 requests	1 minute
`POST /api/v1/embed/*`	20 requests	1 minute

Rate-limited responses return HTTP 429 with Retry-After header.

Frequently Asked Questions

No credit card required. Register with name and email, get an API key, start building.

Yes. Register with a POST to /api/v1/register (name + email) to get your API key. It starts with lc_ and is shown only once. Include it as Authorization: Bearer header in all requests.

Expired forms show an expiration page to humans. The API returns expired: true. A background job permanently deletes all data and uploaded files after expiration.

Yes. Resubmission is allowed and overwrites the previous response. The latest submission is always the one returned by the API.

Two ways: (1) Poll the /summary or /results endpoint, or (2) provide a webhook_url when creating the form. We'll POST to it on every submission.

The POST body contains form_token, recipient_uuid, submitted_at, and response_json with the structured data. Retries use exponential backoff (up to 3 attempts).

Yes. Each field supports validation options: required, min_length, max_length, pattern (regex), min_items, and max_items for checkbox groups.

Yes. POST to /api/v1/forms/{token}/recipients with a count parameter. New UUIDs are returned. Up to 10,000 recipients per form.

Yes. Pass a recipients array with prefill objects when creating a form or adding recipients. You can also provide your own UUIDs. Prefilled values appear as defaults that the user can change.

Yes. Pass a theme_color hex value when creating the form. The hosted page and embed widget both adapt to your color.

Schema supports file fields with configurable accept types and size limits. Files are stored on disk and returned as base64 via the API when include_files=1.

Schema definitions are limited to 50KB. Individual file uploads are limited to 10MB. Maximum 10 files per submission.

Yes. Send a DELETE request with the X-Delete-Token header. All data and files are permanently removed.

Data is stored on a Hetzner server in Germany. Files are stored on local disk. All data is deleted after the retention period expires.

Ready to Close the Loop?

Get an API key and start building in under a minute.

Get Your API Key →

No credit card. No dashboard. Just curl and an API key.

Human-in-the-Loop for AI Agents