URL: https://gofastmcp.com/apps/providers/form
Title: Form Input - FastMCP

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Field mapping
Callback
Configuration
Multiple forms
Prefab Providers
Form Input
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Collect structured data from users via Pydantic models
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New in version
3.2.0
FormInput
generates a validated form from a Pydantic model. The user fills it out, and the submission is validated against the model before being returned. Structured elicitation that can’t be hallucinated.
from
typing
import
Literal
from
pydantic
import
BaseModel
,
Field
from
fastmcp
import
FastMCP
from
fastmcp
.
apps
.
form
import
FormInput
class
BugReport
(
BaseModel
):
title
:
str
=
Field
(
description
=
"
Brief summary
"
)
severity
:
Literal
[
"
low
"
,
"
medium
"
,
"
high
"
,
"
critical
"
]
description
:
str
=
Field
(
description
=
"
Detailed description
"
,
json_schema_extra
={
"
ui
"
:
{
"
type
"
:
"
textarea
"
}},
)
mcp
=
FastMCP
(
"
My Server
"
)
mcp
.
add_provider
(
FormInput
(
model
=
BugReport
))
This registers two tools:
Tool
Visibility
Purpose
collect_bugreport
Model
Opens the form UI
submit_form
App only
Validates and processes the submission
The tool name is derived from the model class name, lowercased:
collect_{modelname}
. So
BugReport
becomes
collect_bugreport
,
ShippingAddress
becomes
collect_shippingaddress
. Use
tool_name
to override if needed. The LLM calls it with a prompt explaining what it needs, and the user gets a form with fields matching the model.
​
Field mapping
FormInput
uses Prefab’s
Form.from_model()
, which maps Pydantic types to form components:
Python type
Form component
str
Text input
int
,
float
Number input
bool
Checkbox
datetime.date
Date picker
Literal[...]
Select dropdown
SecretStr
Password input
Use
Field()
metadata to control labels (
title
), placeholders (
description
), and validation (
min_length
,
max_length
,
ge
,
le
). Use
json_schema_extra={"ui": {"type": "textarea"}}
for multiline text.
​
Callback
By default, the validated model is returned as JSON. Provide an
on_submit
callback to process the data server-side:
def
save_report
(
report
:
BugReport
)
->
str
:
db
.
insert
(
report
.
model_dump
())
return
f
"Bug #
{
db
.
last_id
}
filed:
{
report
.
title
}
"
mcp
.
add_provider
(
FormInput
(
model
=
BugReport
,
on_submit
=
save_report
))
The callback receives a validated model instance and returns a string that becomes the tool result.
​
Configuration
FormInput
(
model
=
BugReport
,
# Required: the Pydantic model
name
=
"
BugTracker
"
,
# App name (default: model name)
title
=
"
File a Bug
"
,
# Card heading (default: model name)
tool_name
=
"
file_bug
"
,
# Tool name (default: collect_{model})
submit_text
=
"
Submit Report
"
,
# Button label (default: "Submit")
on_submit
=
save_report
,
# Optional callback
send_message
=
True
,
# Push result as a chat message
)
Set
send_message=True
to push the result back into the conversation via
SendMessage
, triggering the LLM’s next turn. Without it, the result is just the tool return value.
​
Multiple forms
Add multiple providers for different models — each gets its own tool:
mcp
=
FastMCP
(
"
My Server
"
,
providers
=[
FormInput
(
model
=
ShippingAddress
),
FormInput
(
model
=
BugReport
),
FormInput
(
model
=
ContactInfo
),
],
)
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