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.
npx skills add rpraharaj/forward-deployed-engineer --skill contract-designgit clone --depth 1 https://github.com/rpraharaj/forward-deployed-engineerWrote 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.
[](https://agentmods.dev/skills/rpraharaj/forward-deployed-engineer/contract-design)<a href="https://agentmods.dev/skills/rpraharaj/forward-deployed-engineer/contract-design"><img src="https://agentmods.dev/badge/skills/rpraharaj/forward-deployed-engineer/contract-design.svg" alt="Measured on agentmods" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00103 | $0.02219 |
| Opus 5 | $0.00051 | $0.01110 |
| Sonnet 5 | $0.00021 | $0.00444 |
| Haiku 4.5 | $0.00010 | $0.00222 |
Grade A, and why
contract-design 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 7d 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.
How it starts
The opening of the file, as written. The whole thing — 189 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Contract design
Designing something other people depend on.
Why this exists
An internal interface can be changed by editing every caller. A published contract cannot, and the moment consumers exist outside your repository the constraints change completely: you no longer control when they upgrade, whether they upgrade, or in some cases who they are.
The characteristic mistake is designing a contract as though it were an internal interface — shaped for the current implementation, with no versioning story — and discovering the constraint when the first breaking change is needed. By then the options are all expensive.
An FDE hits this specifically because you often can't see the consumers. blast-radius ring 4 is the hardest ring to establish from inside one repository, and contracts are exactly where an unknown consumer hurts.
When this applies
- Creating or changing an API, event, message, or shared schema
- Adding a field to a published response or event payload
- Consumers exist outside your repository
- "How should we version this?"
- Anything crossing a team boundary
When it doesn't
- Internal interfaces with all callers in one repository — refactor freely
- A prototype nobody consumes yet
- The contract exists and isn't changing — that's
blast-radius
Prerequisites
- Locate the workspace:
FDE_WORKSPACE, else the charter Location, else.fde/, else../<repo>-fde/ .fde/06-blast-radius-*.md— ring 3 and ring 4 especially. You need the consumer list before designing. If ring 4 was not checked, design as if consumers are uncontrollable..fde/03b-nfrs.md— data classification determines what may cross the boundary.fde/02b-ownership.md— who must be coordinated with
Procedure
1. Establish who consumes it, and how much control you have
This determines everything downstream, and the categories behave very differently:
| Consumer type | Control | Implication |
|---|---|---|
| Same team, same repo | Full | Change freely; this isn't really a contract |
| Other team, same org | Coordinated | Breaking changes possible with notice and effort |
| External partner | Contractual | Breaking changes need commercial agreement |
| Mobile or embedded client | None | Old versions live forever. Design for indefinite compatibility. |
| Unknown | None, and you can't ask | Treat as the most constrained case |
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.
- 7d ago First seen · 189 lines · 103 tokens per session scan A 49f49faf72d6
contract-design is a skill published in the GitHub repository rpraharaj/forward-deployed-engineer (6 stars, last pushed 20d ago), licensed MIT. It adds 103 tokens to every session and 2,219 once invoked, about $0.0005 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 2026-08-31.
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