Playbook

Create custom field

create_custom_field

DestructiveIdempotent

Create a custom field on a workspace, or REPLACE the options of one that already exists. Matching is by name: if a select field with this name exists, its option list is overwritten and every option missing from options is deleted, taking that value off every asset holding it. Always pass the complete intended option set, and check list_custom_fields first when the field may already exist. The workspace's built-in 'Status' field cannot be replaced through this tool; use update_asset_status to assign its value to an asset. For a select field (the default) options cannot be empty. For a date, person or url field pass field_type and no options; an existing field with the same name and type is returned unchanged, and a name already used by a field of another type is refused. A NEW field is refused once the workspace reaches its plan's custom field quota — replacing the options of an existing field still works at the limit, so check list_custom_fields before assuming the workspace needs another field. A field's VALUE is set on an asset with update_asset's fields argument ({ "Priority": "High" }); there is no separate set-value tool. Field and option names are matched EXACTLY; update_asset answers an unknown one with an error naming the valid ones, and list_custom_fields has the spelling. Requires a write-scope token and workspace owner/admin permission.

Input Schema

TableJSON Schema

Name	Required	Description
`name`	Yes	Field name, e.g. 'Priority'. An existing field with this name is reused and its options replaced. The built-in 'Status' field is protected and cannot be replaced.
`options`	No	The complete set of values a select field allows, e.g. ['Low', 'Medium', 'High']. Replaces the existing options; anything omitted is deleted. Required and non-empty for a select field; omit it for date, person and url fields.
`field_type`	No	What the field holds: 'select' (default) for a fixed set of options, 'date' for an ISO date, 'person' for a workspace member, 'url' for a link. Cannot be changed later.
`organization`	No	Workspace slug, as returned by list_organizations. Omit it when the account has a single workspace — it is then resolved from your token. Pass it only when the account has several, or when you mean a workspace other than the obvious one.

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedOct 5, 2026

addedInput schema / additionalProperties
```
Added value: +false
```

removedInput schema / properties / context

Removed value: -{
-  "description": "Explain why you are calling this tool and how it fits into the user's overall goal. This parameter is used for analytics and user intent tracking. YOU MUST provide 15-25 words (count carefully). NEVER use first person ('I', 'we', 'you') - maintain third-person perspective. NEVER include sensitive information such as credentials, passwords, or personal data. Example (20 words): \"Searching across the organization's repositories to find all open issues related to performance complaints and latency issues for team prioritization.\"",
-  "type": "string"
-}

changedInput schema / required

Previous value: -[
-  "name",
-  "context"
-]New value: +[
+  "name"
+]

First observedOct 2, 2026

TDQS

A4.8/5.0

Behavior5/5

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

Annotations flag destructiveHint=true and idempotentHint=true, and the description richly corroborates beyond them: it discloses exactly what is destroyed (options omitted are deleted, removing the value from every asset holding it), the plan quota on new fields, auth requirements (write scope + owner/admin), and exact-name matching with error behavior on unknown names. No contradiction with the annotations.

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 primary create/replace behavior, then caveats, quota, and auth. It is dense and long, and a couple of statements (Status-field protection, options replacement) partially restate the schema, but nearly every sentence carries actionable information, so the length is largely earned.

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 four params, one mutation with destructive side effects, no output schema, and a large sibling set, the description covers creation, overwrite semantics, quota limits, auth, sibling routing, and value-setting. An agent has everything needed to call it correctly; the absent output schema is not a gap since nothing about the response is required to invoke it.

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

Parameters4/5

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

Schema coverage is 100%, so the per-parameter detail largely duplicates schema text, but the description adds cross-parameter semantics: the field_type/options dependency (select needs non-empty options; date/person/url pass field_type and omit options), the unchanged return for a same name+type field, and refusal when the name belongs to another type. That is genuine meaning beyond the schema, though much overlaps.

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?

The opening sentence gives a specific verb (Create / REPLACE) and resource (custom field on a workspace), and immediately distinguishes the dual create-or-overwrite behavior. It differentiates itself from siblings by naming delete_custom_field's counterpart (list_custom_fields), update_asset_status, and update_asset explicitly, so an agent can route without opening another 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?

Explicit when-to-use and when-not guidance: check list_custom_fields first if the field may exist, do NOT use this for the built-in 'Status' field (use update_asset_status), and set a field's VALUE via update_asset's `fields` argument because no separate tool exists. The alternatives are named with the conditions that select them.

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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