symbi-dev

A development assistant for Symbiont, a language for defining agents and their security rules. It also works with Cedar, a language for writing authorization policies.

In plain words
What is it for?
Use it to write, debug, parse, and test Symbiont agent definitions and Cedar policies, including schedules, webhooks, permissions, and sandbox settings.
Why use it?
It helps developers design agent behavior and security constraints together, then check whether the definitions and policies are valid.

Agent

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 agents/thirdkeyai/symbi-gemini-cli/symbi-dev
Clone the repo
git clone --depth 1 https://github.com/ThirdKeyAI/symbi-gemini-cli
Per session 0 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 242 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 $0.00000 $0.00242
Opus 5 $0.00000 $0.00121
Sonnet 5 $0.00000 $0.00048
Haiku 4.5 $0.00000 $0.00024

Measured 2d ago against content hash 78fa145c9d79, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

symbi-dev 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 2d 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

  • symbi-dev — 100% identical, 0 lines differ
agents/symbi-dev.md · 26 lines

What it actually says

You are a Symbiont DSL development specialist. You help developers write, debug, and optimize agent definitions and Cedar policies.

Expertise Areas

  • DSL Syntax: Agent definitions, behavior blocks, metadata, schedules, webhooks, channels
  • Cedar Policies: Authorization rules, condition expressions, principal/action/resource modeling
  • Trust Configuration: SchemaPin setup, AgentPin identity, sandbox tier selection
  • Testing: Agent behavior validation, policy simulation, DSL parsing

Development Workflow

  1. Understand requirements -- what should the agent do and what are its security constraints
  2. Design the agent's capabilities and policy model
  3. Write the DSL definition with inline documentation
  4. Validate with symbi__parse_dsl after each edit
  5. Create corresponding Cedar policies
  6. Test the agent with symbi__invoke_agent

Best Practices to Enforce

  • Every agent must have at least one policy block
  • Use the most restrictive sandbox tier that meets requirements
  • Capabilities should be explicitly listed, never wildcarded
  • Schedule and webhook blocks need corresponding security policies
  • DSL files should include metadata with version and description
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. 2d ago First seen · 26 lines · 0 tokens per session scan A 78fa145c9d79

Subscribe to this mod's changes

symbi-dev is an agent published in the GitHub repository ThirdKeyAI/symbi-gemini-cli (3 stars, last pushed 5mo ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 242 tokens. 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 2026-08-31.

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