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

With readOnlyHint=true already declaring the safe-read profile, the description adds real value by disclosing the payload shape: the returned record includes 'custom fields, tags and links', which matters since no output schema exists. It stops short of 5 only because it says nothing about missing-id behavior or errors.

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 tight sentences with the fetch behavior front-loaded; the trailing 'Insightly: GET /<Object>/{id}' is largely redundant with the prose, but it costs little and confirms the underlying call.

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 two-parameter read with full schema coverage and no output schema, the description covers the return payload (custom fields, tags, links), which is the main missing piece. Error and not-found behavior remain unaddressed, keeping it from a 5.

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 the object enum is fully documented in the input schema, so baseline 3 applies. The description's 'by id' and record-type list merely restate what the schema already provides.

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 and resource: 'Fetch a single ... by id' and enumerates the eight supported record types, which distinguishes it from insightly_list_records and insightly_search_by_tag. The differentiation is implicit (via 'single' + 'by id') rather than an explicit contrast, so it stops short of a 5.

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?

Usage is only implied by the 'by id' phrasing — an agent can infer it is the lookup-by-identifier counterpart to the list/search tools, but the description never states when to prefer it over insightly_list_records or insightly_search_by_tag, nor any prerequisites.

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