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

readOnlyHint=true already tells the agent this is a safe read, so the description's burden is lower. It adds the returned field shape and the underlying endpoint, but says nothing about result volume, paging behavior (despite a skip param), or instance-wide scoping.

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?

Two short sentences with zero padding and the purpose front-loaded. The trailing endpoint note is mildly redundant but cheap and useful for API-literate agents.

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 trivial read-only list tool with no output schema, stating the returned fields plus the schema's paging params covers what an agent needs. Only the absence of any usage/routing context keeps it short of complete.

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% and both parameters (top, skip) are documented in the schema with ranges and defaults. The description adds no parameter guidance, so the 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?

States a specific verb+resource ("List the lead sources defined in the instance") and even enumerates the returned fields (LEAD_SOURCE_ID, name), which separates it cleanly from the sibling insightly_list_lead_statuses. An agent can identify what this returns without opening the schema.

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?

There is no when-to-use guidance and no alternative named. A reasonable agent will infer it's for retrieving lead-source IDs to feed into create/update calls, but the description never states that use case or when it should be preferred over insightly_list_lead_statuses or insightly_list_records.

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