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Tesslate OpenSail

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What a skill is

A skill is a markdown document that teaches an agent a reusable capability. It has a name, a short description, and a body. The body can be anything that packages up working know-how: a code-review checklist, a research methodology, a data-analysis pipeline, a writing style, a report template, a step-by-step playbook for a recurring task. Skills are the unit of portable agent knowledge in OpenSail. Build a skill once, attach it to any agent, share it on the marketplace.

Author once

Capture an entire methodology in a markdown file

Reuse everywhere

Attach to any agent on any project

Progressive loading

Only the name and description live in context; the body loads on demand

Shareable

Install open-source skills from the marketplace or publish your own

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Progressive loading

Context windows are finite. Injecting every skill body at session start wastes tokens on capabilities the agent never uses. OpenSail solves this with progressive disclosure:
1

Catalog injected at session start

When a chat session opens, the orchestrator discovers every skill available to the agent and injects a lightweight catalog into the system context: name, one-line description, source tag. Full bodies are not loaded.
2

Agent decides when it needs one

As the agent works, it scans the catalog for a relevant skill. When it finds one, it calls the load_skill tool with the skill slug.
3

Body loaded on demand

The orchestrator fetches the full body, applies any live marker substitutions (so built-in skills always match current platform behavior), and returns it to the agent as a tool result.
4

Used in the next turn

The agent now has the full skill body in context and can apply it. The body stays in context for the rest of the session or until compaction.
Progressive loading is automatic. Skill authors don’t do anything special. Agents don’t need special training. The load_skill tool and the catalog injection handle it transparently.

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The three skill sources

Every agent session merges skills from three independent sources into one catalog:
SourceWhere it livesWho sees it
Built-inSeeded by the platform (is_builtin=True)Every agent, every user
Database assignmentAgentSkillAssignment rows created when you install a skill on an agentOnly agents you’ve attached it to
Project file.agents/skills/SKILL.md inside the workspaceAny agent working in that project
Duplicates are de-duplicated. If a user has both a built-in skill and an explicit assignment to the same skill, it appears once, tagged built-in.

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Browsing and installing skills

1

Open the marketplace

Marketplace tab, then filter to Skills. Browse by category, tag, or creator.
2

Open a skill

The detail page shows the skill body, the creator, the tags, and installation stats.
3

Install

Click Install. The skill lands in your Library with your ownership.
4

Attach to an agent

Open the agent you want to extend. In the Skills tab, click Add Skill and pick from your Library.
5

Use it

Start a chat session with that agent. The skill is in the catalog from the first turn.

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Authoring a skill

Skills are plain markdown with a lightweight frontmatter contract.
1

Pick a slug

Stable kebab-case identifier. Example: react-component-review.
2

Write a one-line description

This is what the agent reads to decide whether to load the body. Make it concrete. “Checklist for reviewing React components for accessibility and performance” beats “reviews code”.
3

Write the body

Treat it like documentation for a junior engineer who needs to follow your methodology exactly. Include examples, anti-patterns, and edge cases. Markdown code fences and tables are fine.
4

Publish

Open the Library, create a new skill, paste the body, save. Optionally submit it to the marketplace.

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What makes a good skill body

“Run npm test -- --coverage and fail the review if coverage drops below 80%” beats “make sure there are enough tests”.
The agent executes top to bottom. Structure the body as a numbered or bulleted sequence the agent can walk through.
Paste short code samples or CLI transcripts showing what correct output looks like. LLMs pattern-match examples better than abstract instructions.
Spelling out what not to do is as valuable as what to do. “Never use any in TypeScript code” is a skill rule that saves turns.
One skill per capability. If the body grows past a few hundred lines or covers multiple methodologies, split it into multiple skills.

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Tesslate skills vs open-source skills

Shipped with the platform. Authored by the Tesslate team. Available to every agent without any attachment. Live-rendered: marker tokens like {{TESSLATE_CONFIG_SCHEMA}} or {{SERVICE_CATALOG}} are substituted with current values from the code, so skill bodies never drift from the actual platform behavior.Examples:
  • project-architecture (how OpenSail projects are structured)
  • Config schema skills that reflect the live .tesslate/config.json definition

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Project-file skills

Any agent working in a project picks up skills from .agents/skills/SKILL.md automatically. This is how you ship project-specific know-how with the repo itself. 
your-project/
├── .agents/
│   └── skills/
│       ├── run-migrations.md
│       ├── deployment-checklist.md
│       └── review-pr.md
├── src/
└── package.json
Commit these files to git. Anyone working in the project with any agent gets the same skills. No install step required.

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Publishing a skill

1

Write and test

Use the skill on real work across multiple projects. Refine the body based on where the agent gets stuck or drifts.
2

Submit

Open the skill in your Library and click Publish. Fill in the marketplace description, tags, and category.
3

Set visibility

Private, team, or public. Public goes through the approval pipeline.
4

Iterate

Ship updates as new versions. Installers can pin a version or auto-update.

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Best practices

The agent only knows the description. If your description is vague, your skill won’t get loaded when it’s needed. Make it specific and action-oriented.
Long bodies burn context once loaded. Aim for the shortest body that fully captures the methodology. If multiple sub-methods are inside, consider splitting.
A single agent can load many skills in one session. Prefer several small focused skills to one giant skill covering everything.
Skills that work with one agent’s system prompt may conflict with another’s. If you publish a skill, test it against the default agents users will pair it with.

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Next steps

Customizing Agents

Attach skills to your own custom agents

Connectors (MCP)

Pair skills with connectors for end-to-end workflows

Using Agents

Watch the load_skill tool in action

Marketplace

Browse published skills