JSONPad

Create an item

create_item

Add an item to a list. The data is checked against the list's schema and its write rules (rule lookups cost 1 request per item they read). Strings in the data can be $jsonpad-var: variables, substituted when the item is saved, e.g. "$jsonpad-var:now", "$jsonpad-var:now(+5m)", "$jsonpad-var:uuid", "$jsonpad-var:random-integer(1, 100)" (see the docs for the rest). Returns the new item's metadata (and data with returnData) and its etag. 1 request.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "list": "<list>"
    },
    "name": "create_item"
  }
}

Input Schema

Name	Required	Description
`data`	No	The item's data: any JSON value, usually an object
`list`	Yes	The list: its id or pathName
`tags`	No	Tags (at most 20). Replaces the existing tags
`version`	No	A version label for the item
`readonly`	No
`activated`	No
`returnData`	No	Return the item's data after the write (default: metadata only)
`description`	No

Output Schema

Name	Required	Description	Default
`etag`	Yes
`item`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 2, 2026

TDQS

A4/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover safety (readOnlyHint=false, destructiveHint=false, idempotentHint=false). The description adds meaningful context: schema and rule validation of data, rule lookup cost per item read, and variable substitution semantics with examples. It also mentions return of metadata and etag. This goes beyond annotations and aids correct invocation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the core action and carefully includes cost and return info, but the sentence about variable substitution is lengthy and could be tightened. Overall, no wasted words for the complexity involved.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity (8 params, rule validation) and the presence of an output schema, the description covers what an agent needs: validation, cost, variable substitution, and return shape. It doesn't need to explain return values further because an output schema exists.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 63%, so the schema documents most parameters. The description adds detail about $jsonpad-var syntax but doesn't clarify other parameters like readonly or activated beyond their schema presence. Baseline 3 is appropriate given partial coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Add an item to a list'), consistent with title and annotations. Distinguishes from siblings like update_item, merge_item_data, patch_item_data, replace_item_data by being the create operation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when to use it (creating a new item), but doesn't explicitly differentiate from other write tools or state preconditions like required permissions. It's adequate but leaves the agent to infer when to choose create_item versus update_item.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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