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formhaus-mcp

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TypeScript
Hybrid

Validate a Formhaus definition

validate_definition
Read-only

Validate Formhaus form definitions against JSON Schema and engine rules before simulation or publishing; get errors, warnings, and repair patches.

Instructions

Call this after writing or editing a definition and before simulate_path or publish_form; it checks the structure and engine rules, while simulate_path checks how a user moves through the form. Checks a Formhaus form definition against the JSON Schema and the engine. Returns { valid, issues }. Each issue has code, severity ("error" or "warning"), a JSON pointer path, message, hint and, when a repair is known, fixes: a list of { title, safe, patch } where patch is an RFC 6902 JSON Patch. Errors make the engine reject the definition, such as a condition with zero or two operators, a condition on a later step, a duplicate key, a route to an earlier step, a condition outside a group on a field inside it (group-scope) or a section inside a section (invalid-nesting). Warnings point to likely mistakes, such as a condition value that is not an option, a select without options or next: false without an autoAdvance radio. Fix each error at its path, or apply one of its fixes, and call again. To apply every safe fix at once, call fix_definition.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
definitionYesFormhaus form definition as a JSON object or a JSON string. JSON Schema: https://formhaus.dev/schema/form-definition.json. Top level: id, title, submit { label }, and fields (one step) or steps [{ id, title, fields }]. Field: { key, type, label, validation?, options?, show?, showAny? }. Rules go inside "validation": { required, minLength, maxLength, min, max, pattern, matchField }. Condition: { field, eq | neq | in | notIn | notEmpty | gt | gte | lt | lte } with exactly one operator, on a field of the same or an earlier step. Optional: lang, messages and labels catalogs, and i18n objects that map texts to translation keys.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
validYesfalse when at least one issue has severity "error".
issuesYesErrors first, then warnings. Fix every error at its path and validate again.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.13.3
    • addedOutput schema / properties / issues / items / properties / fixes
      Added value: +{
+  "description": "Ready repairs for this issue. Apply one patch to the definition, then validate again.",
+  "items": {
+    "additionalProperties": false,
+    "properties": {
+      "patch": {
+        "description": "RFC 6902 JSON Patch operations (add, replace, remove, move) with JSON pointer paths.",
+        "items": {
+          "additionalProperties": {},
+          "propertyNames": {
+            "type": "string"
+          },
+          "type": "object"
+        },
+        "type": "array"
+      },
+      "safe": {
+        "description": "true when applying the patch only repairs the issue and changes nothing else. fix_definition applies these.",
+        "type": "boolean"
+      },
+      "title": {
+        "type": "string"
+      }
+    },
+    "required": [
+      "title",
+      "safe",
+      "patch"
+    ],
+    "type": "object"
+  },
+  "type": "array"
+}
  2. First observedv0.13.1

TDQS

A4.6/5.0
Behavior5/5

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

Annotations only declare readOnlyHint=true; the description goes far beyond that by specifying the return shape { valid, issues }, the difference between errors (engine rejects the definition) and warnings (likely mistakes), enumerated error codes, the repair mechanism (RFC 6902 JSON Patch with a 'safe' flag), and the re-validate loop after fixing.

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-loaded with the call-order guidance and the return contract before the long enumerations of error and warning codes. The code lists are dense and somewhat verbose but each example earns its place by telling the agent what a rejection actually looks like.

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?

An output schema exists and the description still summarizes the return value; for a single-parameter validation tool with annotations covering safety, nothing an agent needs to call it correctly or interpret the result is missing.

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% and the single 'definition' parameter carries an extensive inline schema description (top-level keys, field shape, condition operators, validation rules), so the description need not compensate. The description's phrasing ('after writing or editing a definition') adds workflow context but no new parameter syntax.

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 precise verb+resource (validates a Formhaus form definition) and explicitly distinguishes itself from siblings: it checks structure and engine rules 'while simulate_path checks how a user moves through the form.' An agent can separate it from simulate_path, fix_definition and publish_form without opening any schema.

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

Usage Guidelines5/5

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

Gives explicit sequencing ('after writing or editing a definition and before simulate_path or publish_form') and names the alternative paths, including 'To apply every safe fix at once, call fix_definition.' When-to-use, when-not-to-use and the alternative are all present.

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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