MCP Linear

linear_updateIssueCustomField

Idempotent

Update or clear a custom field value on a Linear issue. Pass null to remove the existing value.

Instructions

Set or clear a custom field value on an issue. Pass null as value to clear it.

Input Schema

TableJSON Schema

Name	Required	Description
`value`	Yes	JSON-compatible value to write. Use null to clear the field. Arrays and objects are passed through as-is when the Linear schema accepts them.
`issueId`	Yes	ID or identifier of the issue whose custom field should be updated
`customFieldId`	Yes	ID of the custom field definition to update

Output Schema

TableJSON Schema

Name	Required	Description	Default
`raw`	No
`value`	No
`issueId`	No
`success`	No
`currentValue`	No
`customFieldId`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.4.3Sep 24, 2026

TDQS

B3.4/5.0

Behavior3/5

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

Annotations already indicate a write operation (readOnlyHint=false) and idempotency (idempotentHint=true). The description adds the explicit null-clearing behavior, which is also in the schema, so it provides marginal value beyond annotations. It doesn't mention permissions or failure modes, but the annotations cover the safety profile adequately.

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?

A single sentence that front-loads the main action ('Set or clear a custom field value') and includes the key edge case (null to clear) immediately. Zero filler words; every part earns its place.

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 simple mutation tool with fully documented parameters and an output schema, the description is sufficient. However, it does not reference sibling tools like linear_getCustomFields for field discovery or clarify that it only works on issue custom fields (implied by name). This is a minor gap but not critical.

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%, with each parameter already thoroughly described including the JSON-compatible value types and null clearing. The tool description adds nothing beyond the schema, meeting the baseline for full coverage without redundant detail.

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?

The description clearly states the verb 'Set or clear' and the resource 'custom field value on an issue', which distinguishes it from siblings like linear_updateIssue that handle standard fields. It is specific but could more explicitly contrast with that sibling. The action and target are unambiguous.

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

Usage Guidelines2/5

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

No guidance is provided on when to use this tool versus alternatives like linear_updateIssue, nor does it point to discovery tools like linear_getCustomFields. The only usage hint is the null-to-clear behavior, which is more of a parameter detail than a usage guideline.

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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