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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavioral detail with no output schema present: unknown values return null and placeholders indicate coming-soon status, which tells the agent how to interpret sparse results rather than misread them as errors or missing data.

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?

Three short sentences, front-loaded with the core action and followed by two clauses that each carry distinct information (null semantics, placeholder semantics). Nothing is repeated from the name, title or schema.

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 full annotation coverage and no output schema, the description adequately covers what is returned and how ambiguous values are represented. Minor gaps remain around invalid-slug behavior and the expected source of the slug, but nothing essential to invoking it correctly is missing.

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 0% and the single parameter carries only minLength/maxLength constraints. The description says 'by slug', identifying the lookup key's role and tying it to the identifier produced by the search tools, but adds no format, case-sensitivity or length guidance, so it only partially compensates for the coverage gap.

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 ('Get a source by slug') and enumerates the payload ('provenance, score breakdown and access requirements'), so the agent knows this is a detail lookup rather than a list. It does not explicitly name search_sources or top_sources as the alternatives, leaving the distinction to inference from 'by slug'.

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: the phrase 'by slug' signals that the agent must already hold a slug, which typically comes from search_sources or top_sources, but no when-to-use or when-not-to-use condition is stated. No prerequisites, error handling for an unknown slug, or sibling routing is given.

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