JSONPad documentation

Try a write against write rules

eval_write_rule

Read-onlyIdempotent

Check one write against a rule set, as the API would, and say whether it would be allowed, denied (403) or failed (400), which statement decided it, and (with trace) what every expression evaluated to. The write is shaped like a rule test case: action, identity, token, old, new, patch, merge, now. Costs nothing and sees no data.

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": {
      "rules": "<rules>",
      "write": "<write>"
    },
    "name": "eval_write_rule"
  }
}

Input Schema

Name	Required	Description
`items`	No	Items for lookups to find: { "<list>": { "<item id or alias>": { "data": ... } } }
`rules`	Yes	The rule text, or its lines as an array (as in a schema sync document)
`trace`	No	Include the value of every expression
`write`	Yes	The write to check
`identities`	No	Named identities the write can refer to

Output Schema

Name	Required	Description	Default
`ok`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 30, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so safety is covered; the description still adds real value by clarifying this is a side-effect-free simulation that "sees no data" and explains the trace flag's effect on the response (every expression's evaluated value). It stops short of describing error handling or limits.

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

Conciseness5/5

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

Two sentences, zero filler, and the core purpose plus outcomes are front-loaded before the write-shape detail. Every clause contributes.

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

Completeness4/5

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

For a 5-parameter nested tool with an output schema, the description covers purpose, outcome semantics and the trace behavior, so an agent has enough to call it correctly. Minor gaps remain around how rules/identities/items interact and how failures are surfaced.

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 description coverage is 100%, so the schema already documents rules, items, identities, trace and the nested write fields; the baseline is 3. The description adds only a prose enumeration of the write shape (action, identity, token, old, new, patch, merge, now), which largely restates what the schema already says.

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

Purpose4/5

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

States a specific verb (check/evaluate) and resource (one write against a rule set) and enumerates the three outcomes it reports (allowed, 403 denied, 400 failed) plus which statement decided it. It is clear what the tool does, though it never explicitly contrasts itself with the close sibling check_write_rules.

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?

"As the API would" and "costs nothing and sees no data" imply this is a safe dry-run/simulation for pre-flighting a write, which hints at when to reach for it. However, there is no explicit statement of when to use it versus check_write_rules or validate_sync_document, and no exclusions.

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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