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Backlog MCP Server

get_custom_fields

Retrieve custom fields for a Backlog project using either project ID or key to configure issue tracking and data collection.

Instructions

Returns list of custom fields for a project

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
projectIdNoThe numeric ID of the project (e.g., 12345)
projectKeyNoThe key of the project (e.g., 'PROJECT')

Implementation Reference

  • The asynchronous handler function that implements the core logic of the 'get_custom_fields' tool: resolves the project identifier using resolveIdOrKey and fetches custom fields via the Backlog client.
    handler: async ({ projectId, projectKey }) => {
      const result = resolveIdOrKey(
        'project',
        { id: projectId, key: projectKey },
        t
      );
      if (!result.ok) {
        throw result.error;
      }
      return backlog.getCustomFields(result.value);
    },
  • Zod-based input schema definition for the tool, specifying optional projectId (number) and projectKey (string) parameters with descriptions.
    const getCustomFieldsInputSchema = buildToolSchema((t) => ({
      projectId: z
        .number()
        .optional()
        .describe(
          t(
            'TOOL_GET_CUSTOM_FIELDS_PROJECT_ID',
            'The numeric ID of the project (e.g., 12345)'
          )
        ),
      projectKey: z
        .string()
        .optional()
        .describe(
          t(
            'TOOL_GET_CUSTOM_FIELDS_PROJECT_KEY',
            "The key of the project (e.g., 'PROJECT')"
          )
        ),
    }));
  • Tool schema configuration: assigns the input schema object, sets output schema to CustomFieldSchema, and lists important output fields.
    schema: inputSchemaObject,
    outputSchema: CustomFieldSchema,
    importantFields: [
      'id',
      'name',
      'typeId',
      'required',
      'applicableIssueTypes',
    ],
  • Registers the get_custom_fields tool by invoking its factory function with Backlog client and translation helper in the 'issue' toolset group.
    getCustomFieldsTool(backlog, helper),
Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states this is a read operation ('Returns'), but doesn't mention authentication requirements, rate limits, pagination, error conditions, or what happens if no custom fields exist. For a tool with zero annotation coverage, this leaves significant gaps in understanding its behavior.

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?

The description is a single, efficient sentence that states the core functionality without unnecessary words. It's appropriately sized and front-loaded with the essential information, making it easy to parse quickly.

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

Completeness3/5

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

Given the tool's moderate complexity (2 parameters, no output schema, no annotations), the description is minimally adequate but incomplete. It covers the basic purpose but lacks behavioral context, usage guidelines, and output details that would help an agent use it effectively in a broader workflow.

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 both parameters ('projectId' and 'projectKey') clearly documented in the schema. The description doesn't add any additional parameter semantics beyond implying these identify a project, so it meets the baseline of 3 where the schema does the heavy lifting.

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 ('Returns') and resource ('list of custom fields for a project'), making the purpose specific and understandable. However, it doesn't explicitly differentiate from sibling tools like 'get_project' or 'get_issue_types' that might also return project-related data, preventing a perfect score.

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?

The description provides no guidance on when to use this tool versus alternatives. With many sibling tools available (e.g., 'get_project', 'get_issues'), there's no indication of prerequisites, context, or exclusions for selecting this specific tool over others.

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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