agent-builder

agent-builder is a skill for Claude Code, Codex from TesslateAI/OpenSail. It costs 30 tokens per session (1,586 once invoked), scanned A, original, Apache-2.0.

A drafting tool for creating specialised agents and connecting them to schedules, webhooks, or app events. It creates drafts only, so a person must publish them in the user interface.

In plain words
What is it for?
Use it to draft task-specific agents, attach skills or external tool servers, and set up scheduled or event-based runs. Child agents can be created, but they cannot create further agents.
Why use it?
It removes the need to assemble an agent and its automatic triggers manually. Draft-only operation keeps new agents and automations from becoming public or running before review.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/tesslateai/opensail/agent-builder
Any agent
npx skills add TesslateAI/OpenSail --skill agent-builder
Clone the repo
git clone --depth 1 https://github.com/TesslateAI/OpenSail

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for agent-builder

README.md
[![agentmods](https://agentmods.dev/badge/skills/tesslateai/opensail/agent-builder.svg)](https://agentmods.dev/skills/tesslateai/opensail/agent-builder)
Your own site
<a href="https://agentmods.dev/skills/tesslateai/opensail/agent-builder"><img src="https://agentmods.dev/badge/skills/tesslateai/opensail/agent-builder.svg" alt="Measured on agentmods" height="20"></a>
Per session 30 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,586 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00030 $0.01586
Opus 5 $0.00015 $0.00793
Sonnet 5 $0.00006 $0.00317
Haiku 4.5 $0.00003 $0.00159

Measured 4d ago against content hash 89bfe2ea252b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

agent-builder scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

orchestrator/app/agent/skills/agent-builder/SKILL.md · 150 lines

How it starts

The opening of the file, as written. The whole thing — 150 lines — stays where its author put it; the contents beside it link to each section on GitHub.

When to use

Invoke this skill when the user asks you to:

  • Create a new specialised agent (e.g., "build me a daily standup digester").
  • Wire a schedule, webhook, or app event to an agent so it fires autonomously.
  • Attach a skill or MCP server to an agent you (or the user) own.
  • Request a missing capability before performing a gated action.

Do NOT invoke this skill for:

  • Editing the system prompt of an already-published agent — that requires forking; the UI handles it.
  • Publishing an agent to the marketplace. Publishing is a UI-only action that flips is_published=True after a human review. There is no publish_agent tool.

Hard rules — read before any tool call

  1. Depth-1 cap. You can create child agents and attach schedules to them, but those children cannot themselves spawn grandchildren. The attach_schedule tool rejects depth-2 attempts with code depth_exceeded. The DB also enforces depth IN (0, 1) as a second line of defence.
  2. Drafts only. Every agent and automation you create starts in DRAFT state:
    • MarketplaceAgent.is_published=False — invisible in the public marketplace.
    • AutomationDefinition.is_active=False — never fires. The user must enable both in the UI before anything goes live.
  3. Positive-list inheritance. A child automation's contract MAY only carry scopes from this list: tools.execute, read_file, write_file, bash_exec, web_fetch, web_search, send_message, app.invoke, plus any mcp.* prefix. The non-inheritable scopes you can NOT propagate include marketplace.author and automations.writeattach_schedule rejects child contracts that contain them.
  4. Budget rollup. A child automation's max_spend_per_run_usd must be <= the parent's. Daily spend is debited from BOTH the child's daily counter AND every ancestor in the parent chain — if any counter would go negative the run is paused with paused_reason='parent_budget_exhausted'. You cannot use a child to escape a parent's daily cap.

Read the full file on GitHub · 150 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 150 lines · 30 tokens per session scan A 89bfe2ea252b

Subscribe to this mod's changes

agent-builder is a skill published in the GitHub repository TesslateAI/OpenSail (637 stars, last pushed 3d ago), licensed Apache-2.0. It adds 30 tokens to every session and 1,586 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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