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

readOnlyHint already declares this is a safe read, and the description adds meaningful context beyond that: the returned payload contains contacts, address, balance and paid-to-date. Since no output schema exists, disclosing the response contents is genuinely useful. It omits error behavior (e.g. invalid or unknown id), which keeps it from a 5.

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, zero waste. The verb and scope lead, and the endpoint reference is a compact secondary detail.

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 single-parameter read tool with no output schema, the description covers both what it takes (id) and what it returns (contacts, address, balance, paid-to-date), which is the bulk of what an agent needs. Missing only failure modes and any permission requirements.

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 the single client_id parameter, including its hashed format example. The description only restates 'by id' without adding format or constraint detail, 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 one client by id') and even names the underlying endpoint, so an agent can distinguish it from invoiceninja_list_clients or invoiceninja_create_client at a glance. It stops short of explicitly routing to those siblings, which is the only thing separating it from 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?

The singular scope plus the required id implies 'use this when you already have one client's id and need its detail', which is adequate context. However, there is no explicit when-to-use statement, no mention of when to prefer invoiceninja_list_clients instead, and no preconditions.

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