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

Annotations declare readOnlyHint=false and non-destructive, leaving room for the description to explain the write behavior, which it does: results are stored as JSON and retained for 24 hours, giving the agent a clear expiry horizon. It also notes no API key or account is needed, which is genuine auth context rather than repetition of the annotations. Missing is how the stored matches are retrieved or what identifiers are returned.

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 sentences, front-loaded with the core action and effect, followed by parameter shape. The closing 'No API key, no account and no sign up' is somewhat promotional phrasing, though it does carry usable auth information, so it is not pure waste.

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?

With no output schema and a write-and-store behavior, the description should say what the tool returns and how the stored JSON is later accessed; it only says the matches are stored for 24 hours. Matching semantics that matter to callers (unmatched rows, multiple matches per key, key type coercion) are also absent.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning: it clarifies that keys accepts multiple pairs (compound matching) and gives a concrete example of a pair object, which is more than the schema's per-field text conveys. It stops short of explaining behavior on unmatched rows, duplicate keys, or type mismatches.

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?

The description states a specific verb (match), the resource (rows of two tables), the mechanism (one or more pairs of key columns, like a join), and the effect (matches stored as JSON for 24 hours). No sibling tool performs table matching, so an agent can identify it unambiguously.

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 implied by the 'like a join' framing and the requirement that left/right be lists of row objects, so an agent knows the shape of data this applies to. However, there is no explicit when-to-use or when-not-to-use guidance, no mention of alternatives, and no statement of limits such as table size or row count.

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