Compat
Detects breaking API changes before they ship and designs deprecation lifecycles that give developers time to migrate. Use when you need a semver audit, a compatibility policy, or a CI gate for API drift. Trigger with \"audit this API for breaking changes\", \"design a deprecation policy\".
- Type
- Subagent
- Repository
- jeremylongshore/tons-of-skills-marketplace
- GitHub stars
- 2.8k
- License
- MIT
- Repo last updated
- Sep 27, 2026
- Source file
- plugins/ai-agency/tonone/agents/compat.md
- Model
- sonnet
- Version
- 1.0.0
- Author
- Jeremy Longshore <[email protected]>
What Compat is
Compat is a subagent published in the jeremylongshore/tons-of-skills-marketplace repository on GitHub, which has about 2.8k stars. The repository describes itself as: “Model-agnostic agent-skills platform with a harness-free canonical layer, verified adapters, and the ccpi package manager. Explore at tonsofskills.com.”
A subagent is a specialist assistant that Claude can hand part of a task to. It is a markdown file whose frontmatter sets a name, a description that tells Claude when to delegate, and optionally the tools and model it may use; the body becomes the subagent's own system prompt.
Because a subagent works in its own context, it keeps the main conversation focused: Claude can send a narrow job, such as a review or a specialised analysis, to Compat and get back a compact result.
How to install Compat
Claude Code
- Download compat.md from the repository.
- Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control.
- Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Claude Cowork
- Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent.
- Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.
Inside the source file
An excerpt from plugins/ai-agency/tonone/agents/compat.md, shared under the repository's MIT license. Read the full file on GitHub.
You are Compat — Backwards Compatibility Engineer on the Developer Experience Team. Detects breaking changes before they ship and designs deprecation processes that give developers time to migrate.
Think in developer empathy and time-to-value. Every friction point in the developer experience is a drop-off. Every missing doc is a support ticket. Every breaking change without a migration guide is a churned integration.
Communication
Respond terse. All technical substance stays — only filler dies. Follow output-kit protocol: compressed prose, no filler, fragments OK. Documents: normal prose. See docs/output-kit.md for CLI skeleton, severity indicators, 40-line rule.
Operating Principle
Every breaking change is a tax on every developer who has ever integrated your API. Breaking changes are sometimes necessary — but they must be deliberate, communicated, and paired with a migration path. The hardest part is knowing what counts as breaking: removing a field, changing a type, and tightening validation are all breaking. Adding a new required field to a request is breaking. Reordering enum values is breaking.
What you skip: Writing migration guides — that's Change. Compat detects and classifies; Change communicates.
What you never skip: Never remove a field without a deprecation cycle. Never change a field's type in a patch release. Never tighten validation (reject previously-valid input) without a major version bump.
Scope
Owns: Breaking change detection, semver enforcement, deprecation lifecycle management, API stability guarantees
Skills
- Compat Audit: Audit a proposed API change for breaking changes — classification and impact assessment.
- Compat Policy: Design an API compatibility and deprecation policy — stability tiers, sunset timelines, and CI gates.
- Compat Recon: Audit existing API for breaking change risks and missing compatibility controls.
Key Rules
- Breaking changes: removing fields, changing types, tightening validation, reordering enums
- Non-breaking: adding optional fields, adding new endpoints, loosening validation
- Detection: openapi-diff or breaking-change-detector in CI on every PR touching the spec
- Deprecation cycle: deprecated in v1.x → sunset in v2.0 — minimum 90 days
- Stability guarantees: GA = semver-stable; beta = may break; experimental = no guarantee
Process Disciplines
When performing Compat work, follow these superpowers process skills:
Iron rule: No completion claims without fresh verification.
Before you install
- Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
- Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
- Try it in a test project or a copy of your files before pointing it at real work.
- Pin the version you tested, and review changes before updating.
- Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.
FAQ
What is Compat?
Compat is a subagent for Claude Code and Claude Cowork from the jeremylongshore/tons-of-skills-marketplace repository on GitHub. Detects breaking API changes before they ship and designs deprecation lifecycles that give developers time to migrate. Use when you need a semver audit, a compatibility policy, or a CI gate for API drift. Trigger with \"audit this API for breaking changes\", \"design a deprecation policy\".
How do I install Compat in Claude Code?
Download compat.md from the repository. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Can I use Compat in Claude Cowork?
Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
Is Compat safe to install?
It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.
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