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

Annotations already declare readOnlyHint=false, idempotentHint=false and openWorldHint=true, so the bar is lower; the description usefully adds that base defaults to the main branch. However, it says nothing about failure modes (existing PR for the same head, missing permissions) or what the call returns, which matters for a non-idempotent mutation.

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?

One compact sentence with the primary action and key inputs front-loaded; no filler. The parenthetical explanation of head/base is slightly clunky but still earns its place.

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?

A moderately complex mutation with 6 params, no output schema, and annotations covering only the safety profile. The description covers the core flow but omits the return value (PR number/URL) and the draft behavior, so an agent knows how to call it but not fully what to expect back.

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 only 17% (only repo is documented), so the description has to compensate. It does explain head, base, and that title/body carry the change summary and rationale, but it is silent on the draft flag and on whether head accepts owner:branch syntax — leaving 2 of 6 parameters unexplained anywhere.

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 ('Open a pull request from head into base') plus the inputs involved, so an agent can distinguish it from siblings such as gh_pull_merge and gh_pulls. It does not name the siblings explicitly, so it falls just 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?

There is no guidance on when to use this versus gh_pulls (listing PRs), gh_pull_merge (merging), or gh_branch. The agent must infer that 'open' means create, and nothing is said about preconditions like the head branch existing or the PR not already being open.

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