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 bar is lower. The description adds the upstream mapping (FreeAgent: GET /v2/contacts/:id), which is mildly useful, but says nothing about behavior on a missing contact, auth requirements, or rate limits.

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, front-loaded with the action and scope, followed by the endpoint reference. Nothing is padding; every clause carries information.

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 one-parameter read tool with readOnlyHint and full schema coverage, this is nearly sufficient. The only real gap is what the call returns (a contact object) and how a not-found id behaves, which is minor given there is no output schema to defer to.

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 single parameter is already documented as 'numeric id or full FreeAgent URL'. The description's 'by id or URL' merely restates the schema rather than adding format or resolution details, so the baseline 3 applies.

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 contact by id or URL') and implies the single-record scope that separates it from freeagent_list_contacts. It does not name the sibling explicitly, so an agent still has to infer the list-vs-get split.

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: you call it when you already have a contact id or URL. There is no explicit statement of when to prefer this over freeagent_list_contacts (e.g., discovery by name) or any prerequisite/permission context.

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