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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds valuable behavioral context: it reads the last import (not live data), is fast, defaults to active status, and returns a link when nothing is imported. This goes beyond what annotations provide.

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

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

The description is compact and front-loaded with the core purpose, then adds parameter context and edge-case handling. Every sentence earns its place, and the guidance about the 'nothing imported' case is valuable without being verbose.

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

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

For a read-only list tool with 100% schema coverage and no output schema, the description covers the key context: what data is returned, the import-based behavior, defaults, and edge-case handling. It doesn't describe the exact return format, but that's not required given the tool's simplicity and the schema's completeness.

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

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 all four parameters. The description adds some context (status defaults to active, plan narrows to one plan) but doesn't add significant meaning beyond the schema. Baseline 3 is appropriate.

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

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

The description clearly states the tool lists the user's Substack subscribers as imported contacts, with specific fields (name, email, plan, status, subscription date). It distinguishes itself from siblings like get_substack_subscriber_counts and lookup_substack_subscriber by focusing on the imported contacts list.

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

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

The description provides explicit guidance on when to use it: it reads the last import, is fast, and defaults to active status. It also tells the agent what to do if nothing is imported ('give the user the link it returns rather than guessing'), which is actionable guidance beyond just when to use it.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.